AMERICAN MOBILE SATELLITE CORP
8-K, 1997-12-08
COMMUNICATIONS SERVICES, NEC
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                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                    FORM 8-K

                                 CURRENT REPORT

     Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934




                                December 4, 1997
                Date of Report (Date of earliest event reported)



                      AMERICAN MOBILE SATELLITE CORPORATION
             (Exact name of registrant as specified in its charter)



                           DELAWARE 0-23044 93-0976127
(State or other jurisdiction       (Commission               (IRS Employer
    of incorporation)              File Number)             Identification No.)



             10802 Parkridge Boulevard, Reston, Virginia 20191-5416
               (Address of principal executive offices) (Zip Code)



                                 (703) 758-6000
              (Registrant's telephone number, including area code)




<PAGE>


In addition to historical  information, this Current Report on Form 8-K contains
forward-looking  statements  within the meaning of Section 27A of the Securities
Act of  1933  and  Section  21E of the  Securities  Exchange  Act of  1934.  The
forward-looking  statements  contained  herein are subject to certain  risks and
uncertainties  that could cause actual results to differ  materially  from those
reflected in the forward-looking statements.  Readers are cautioned not to place
undue reliance on these forward-looking  statements,  which reflect management's
analysis  only as of the date hereof.  The Company  undertakes  no obligation to
publicly   revise  these   forward-looking   statements  to  reflect  events  or
circumstances that arise after the date hereof.  Readers should carefully review
the risk factors  described in other  documents  the Company  files from time to
time with the Securities and Exchange Commission, including the Form 10-K annual
Report and For 10-Q  Quarterly  Reports filed by the Company prior to this Form
8-K,  any Form 10-Q or Form 10-K filed subsequent to this Current Report on Form
8-K, and any other Current Report on Form 8-K filed by the Company.


Item 5.  Other Events

         On  December  4,  1997,  the  Company  entered  into  two  simultaneous
transactions.  The Company agreed with TMI Communications  and Company,  Limited
Partnership ("TMI"), to acquire a one-half ownership interest in TMI's satellite
(the  "Shared  Satellite",  also  known as  "MSAT-1")  at a cost of $60  million
payable in equal  installments over a five-year period (the "Satellite  Purchase
Agreement");  certain  additional  payments to TMI are contemplated in the event
that  additional  benefits  are  realized  by the  Company  as a  result  of the
contemplated transactions.  Under the Satellite Purchase Agreement, TMI and AMSC
will each own a 50% undivided  ownership interest in the Shared Satellite,  will
be jointly responsible for the operation of the Shared Satellite, and will share
certain satellite operating expenses, but will otherwise maintain their separate
business operations.

         The Shared  Satellite,  originally  designed to have  substantially the
same  capabilities  as the Company's  existing  satellite  ("MSAT-2"),  would be
deployed to cover  substantially the same territory  currently served by MSAT-2.
The  Company  would have the right to use  one-half of the  available  satellite
capacity on the Shared Satellite,  with a right to purchase excess capacity from
TMI on the other half of the Shared Satellite at prices substantially similar to
those in effect under the Company's  existing  Satellite Capacity Agreement with
TMI (the  "Satellite  Capacity  Agreement");  TMI would  have the same  right to
purchase excess  capacity from the Company on its half of the Shared  Satellite,
on the same financial terms. The Satellite  Purchase Agreement provides that the
Satellite  Capacity  Agreement would be suspended upon the Company's purchase of
its one-half interest in the Shared Satellite,  but would again become effective
in the event the  Satellite  Purchase  Agreement is  terminated.  As  previously
disclosed, the Satellite Capacity Agreement between the Company and TMI provides
for backup,  restoral and excess capacity  arrangements  between the Company and
TMI under certain  circumstances  where both the Shared Satellite and MSAT-2 are
operational over North America.

<PAGE>

         Simultaneously,  the Company  entered into an agreement (the "Satellite
Lease Agreement") with African  Continental  Telecommunications  Ltd. ("ACTEL"),
for lease of MSAT-2, for deployment over sub-Saharan Africa. The five-year lease
provides annual lease payments to the Company of $38 million per year; the lease
includes a renewal  option  through  the end of the life of MSAT-2,  on the same
lease terms, at ACTEL's election exercisable 2 1/2 years prior to the end of the
initial lease term.

         Closing under the  Satellite  Purchase  Agreement  and Satellite  Lease
Agreement is subject to a number of  conditions,  including:  United  States and
Canadian  regulatory  approvals;  a  successful  financing  by ACTEL of at least
$120,000,000;  completion of certain satellite testing, inversion and relocation
activities  with respect to MSAT-2,  to support the  contemplated  services over
Africa; receipt of various Gibraltar, South African and other legal requirements
to support  satellite  relocation,  including  with  respect to orbital slot and
spectrum  coordination;  and completion of certain system development activities
sufficient to support satellite redeployment. It is anticipated that the closing
under both agreements will occur simultaneously in the spring of 1998.

         Upon  the closing, the Company will own its half interest in the Shared
Satellite, subject to  the  possibility  of default in the event of a failure to
make  the  required  annual purchase price payments and operational cost sharing
payments for tracking, telemetry and control services ("TT&C") to TMI.  The TT&C
services,  required  to  maintain  and  operate  the Shared Satellite, are to be
provided by Telesat Canada, a company affiliated with TMI.

         If consummated, the transactions are expected to increase substantially
the Company's  revenues,  without anticipated impact to the Company's ability to
serve and grow its  subscribers  based on  expected  capacity  available  on the
Shared  Satellite  (including  excess TMI capacity  available to the Company for
purchase).  As has been previously  reported with respect to MSAT-2,  the Shared
Satellite has  experienced  certain  anomalies in the past and is subject to the
same power management  recommendations as currently in effect for MSAT-2.  While
there can be no assurances of future performance,  the Company believes that the
performance capabilities of the Shared Satellite equal those of MSAT-2.

         The Satellite  Purchase  Agreement and  Satellite  Lease  Agreement are
separate  transactions and reflect separate sets of obligations for the Company.
As a result, it is possible, under certain circumstances, that the Company would
remain  obligated  to make or continue  payments  under the  Satellite  Purchase
Agreement to TMI,  without receipt from ACTEL of anticipated  payments under the
Satellite  Lease  Agreement,  either  because of the  failure by the  Company to
satisfy certain of its obligations to TMI which are not obligations of ACTEL, by
virtue of a  default  by ACTEL or as a result of a  disparate  application  of a
condition or  provision  between the TMI and ACTEL  agreements.  There can be no
assurances  that the  agreements  will operate in parallel,  or that the Company
will not be met  with  certain  completion  or  transactional  risks  under  the
Satellite  Lease  Agreement.  The  Company  has,  however,  included a number of
provisions in each of the two  agreements to mitigate  these risks.  While there
can be no  assurances,  the  Company  believes  that the  significant  financial
benefits  to  be  achieved  through  consummation  of  the  transactions  offset
potential  risks  of an  adverse  impact  to  the  Company  resulting  from  the
transactions.


<PAGE>




                                   SIGNATURES


Pursuant  to the  requirements  of the  Securities  Exchange  Act of  1934,  the
registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned hereunto duly authorized.



                                         AMERICAN MOBILE SATELLITE CORPORATION
                                         (Registrant)



Date: December 8, 1997                    /s/RANDY S. SEGAL
                                          Randy S. Segal
                                          Secretary




<PAGE>

                               EXHIBIT INDEX

Exhibit
Number         Exhibit

10.62  --      Satellite Lease Agreement for the AMSC-1  Satellite,  dated as of
               December  2,  1997,  By and Among  AMSC  Subsidiary  Corporation,
               American Mobile  Satellite  Corporation  and African  Continental
               Telecommunications Ltd. (filed herewith).

 

10.63  --      Satellite  Purchase  Agreement,  dated as of December 2, 1997, By
               and Among TMI Communications and Company, Limited Partnership and
               AMSC  Subsidiary   Corporation  and  American  Mobile   Satellite
               Corporation (filed herewith).

99.14  --      American Mobile  Satellite  Corporation  Press Release No. 97-#22
               dated December 4, 1997 (filed herewith).

99.15  --      American Mobile  Satellite  Corporation  Press Release No. 97-#23
               dated December 4, 1997 (filed herewith).








<PAGE>


                                                            EXHIBIT 10.62


                            SATELLITE LEASE AGREEMENT
                            for the AMSC-1 Satellite



                                  By and Among



                          AMSC Subsidiary Corporation,


                      American Mobile Satellite Corporation


                                       and


                   African Continental Telecommunications Ltd.











                                December 2, 1997



<PAGE>





                                Table of Contents

                                                                          Page  
                                                                          ----
         1   Satellite Lease Agreement
             --  General Terms ...........................................
                 1.1 Satellite Lease Agreement ...........................
                 1.2 Term ................................................
                     (a) Initial Lease Term ..............................
                     (b) Renewal .........................................
                 1.3 Payments From Lessee.................................
             (a) Lease Payments During Lease Term.........................
             (b) Initial Payment..........................................
             (c) Post-Offering Payment....................................
             (d) Initial AMSC Payment Expenses............................
             (e) Treatment of Initial Payment, Post-Offering Payment
                    and Initial AMSC Payment Expenses.....................
             (f) Manner of Payment........................................
             (g) Late Payment.............................................
             (h) Taxes
                 1.4 Return or Retirement of Satellite Upon Expiration of
                        Lease Term or Termination of Lease ...............
   
         2   Steps To Be Taken Before Relocation of Satellite.............
                 2.1 Relocation of Satellite .............................
                 2.2 In-Orbit Insurance ..................................
                 2.3 Lessee to Secure TT&C Facilities and
                        Service to Receive and Operate Satellite .........

         3   Obligations and Covenants of Lessee .........................
                 3.1 Enabling the Satellite to Continue to
                        Occupy Relocated Orbital Position ................
                 3.2 Notice of Problems Involving Satellite...............
                 3.3 Use of Fully-Qualified Personnel.....................
                 3.4 Satellite Operation:  Compliance With Specified Operating
                        Procedures and Applicable Legal Requirements .....
                 3.5 TT&C.................................................
                 3.6 Frequency Coordination...............................
                 3.7 Safe Operation.......................................





                                        i

<PAGE>





                 3.8 Reporting............................................
                 3.9 Government Approvals For Use of Satellite, Etc.......
                 3.10 Additional Guarantees...............................
                 3.11 Cooperation and Support in Obtaining and
                        Maintaining Insurance.............................
                 3.12 Additional Financial Obligations and Covenants......
                      (a) Delivery of Business Plan.......................
                      (b) Delivery of Financial Information...............
                      (c) Actions Requiring Approval of Lessor During Start-Up.
                      (d) Other Actions Requiring Approval of Lessor......
                      (e) Resolution of Disputes..........................
                      (f) Escrow of Securities............................
                      (g) Definitions.....................................

         4   Other Rights and Obligations of Lessor.......................
                 4.1 Rights...............................................
                      (a) Inspection......................................
                      (b) Action to Protect Satellite.....................
                      (c) Testing.........................................
                 4.2 Certain Responsibilities of Lessor...................
                      (a) Documentation...................................
                      (b) Performance Tests...............................
                      (c) U.S. and Canadian Government Approvals
                              For Relocation and Export of the Satellite..
                      (d) Timing of Delivery of Satellite.................

         5   Termination Rights; Effect of Termination; Lease Continuation.
                 5.1 Lessee's Right to Terminate in
                       Certain Circumstances..............................
                 5.2 Lessor's Right to Terminate in
                       Certain Circumstances..............................
                 5.3 Lessor's Right to Terminate in
                       Certain Additional Circumstances...................
                 5.4 Lessor's and Lessee's Rights to Terminate
                       in Event of Total Loss or Constructive Total Loss .
                 5.5 Lessor's Right to Terminate If Lessee's TT&C
                       Contract Is Not In Place...........................
                 5.6 Lease Continuation in Less Than Total or
                       Constructive Total Loss............................

         6   Events of Default; Remedies..................................
             (a) Events of Default........................................
             (b) Remedies.................................................



                                       ii

<PAGE>





         7   Limitation of Liability and Indemnification .................
                 7.1 Limitation on Lessor's Liability.....................
                 7.2 Lessee's Indemnification of Lessor...................
                 7.3 No Consequential, Etc. Damages.......................
                 7.4 Employees of Lessor..................................

         8   Subordination and Assignment ................................
                 8.1 Security Interests and Secured Parties...............
                 8.2 Lessor's Right To Assign.............................
                 8.3 Lessee Assignment....................................

         9   Guarantee of Lessee's Obligations ...........................

         10  Representations and Warranties of AMSC and AMSC Parent.......
                 10.1 AMSC................................................
                 10.2 AMSC Parent.........................................

         11  No Warranties and Representations Relating to the Satellite .
                 11.1  No Warranties......................................

         12  Representations and Warranties of Lessee.....................
                 12.1 Lessee..............................................

         13  General Provisions ..........................................
                 13.1 Binding Effect......................................
                 13.2 Third-Party Rights; Relationship of Parties.........
                 13.3 Notices.............................................
                 13.4 Waiver of Breach/Remedies...........................
                 13.5 Applicable Law......................................
                 13.6 Dispute Resolution..................................
                 13.7 Counterparts and Formal Date........................
                 13.8 Captions............................................
                 13.9 Entire Understanding................................
                 13.10 Dollar Amounts.....................................
                 13.11 Lessee's Payment Obligations.......................
                 13.12 Guarantee of Lessor's Obligations..................
                 13.13 Technical Operations Committee.....................
                 13.14 Lease Characterization.............................





                                       iii

<PAGE>






                                    Exhibits


Exhibit A:              Certain Defined Terms

Exhibit B:              Form of Certificate of Lessee [and Guarantor]

Exhibit C:              Form of Guarantee

Exhibit D:              Choice of Law Agreement





                                    Schedules


Schedule 1.3            Wire Transfer Instructions of the Lessor

Schedule 2.1            Satellite Relocation, Acceptance and Test Plan

Schedule 2.3            Lessee's TT&C Facilities and Services

Schedule 3.8            Reporting Schedule

Schedule 3.12           Officers and Directors Placing Securities in Escrow

Schedule 5.1 and 5.2    Government Approvals and Consents to Relocate
                        the Satellite and Consummate the Lease Transactions

Schedule 10.1           AMSC Consents

Schedule 10.2           AMSC Parent Consents

Schedule 12.1(d)        Lessee Consents

Schedule 12.1(e)        Founders and Their Ownership Interests







                                       iv

<PAGE>




                            SATELLITE LEASE AGREEMENT

         This SATELLITE LEASE  AGREEMENT  ("Lease") is made as of the 2nd day of
December,  1997,  by  and  among  AMSC  Subsidiary  Corporation,  a  corporation
incorporated under the laws of Delaware, with offices located at 10802 Parkridge
Boulevard,  Reston,  Virginia  20191-5416 ("AMSC" or "Lessor");  American Mobile
Satellite  Corporation,  a Delaware  corporation  ("AMSC  Parent");  and African
Continental Telecommunications Ltd., a Gibraltar
company ("Lessee").

     Capitalized  terms used in this  Lease and not  defined  elsewhere  in this
Lease shall have the meanings set forth in Exhibit A.
                                           ---------

                                    RECITALS:

      1.  AMSC is the owner and operator of the Satellite known as "AMSC-1"  or
"MSAT-2," which is currently located in geosynchronous orbit at 101(degree) West
Longitude.

      2.  The Lessee wishes to lease the Satellite from the Lessor and relocate 
it to the Relocated Orbital Position.

      3.  The Lessor is  entering  into a Purchase  Agreement  (the  "Purchase
Agreement") with TMI Communications  and Company,  Limited  Partnership  ("TMI")
pursuant  to which the Lessor  will  purchase a one-half  undivided  interest in
TMI's satellite and transfer all telecommunications  traffic on the Satellite to
the  TMI  Satellite  on or  prior  to the  relocation  of the  Satellite  to the
Relocated Orbital Position.

      4.  The  parties  are  entering  into  this  Lease to set  forth  their
agreement as to the terms and  conditions  upon which the Lessee shall lease the
Satellite from the Lessor.

      NOW, THEREFORE,  for good and  valuable  consideration,  the  receipt  and
sufficiency  of which are  hereby  acknowledged,  the  parties  hereto  agree as
follows:


1.    Satellite Lease Agreement
      -- General Terms
      -------------------------

         1.1 Satellite Lease Agreement.  Subject to the terms and conditions of 
             -------------------------  
this Lease, the Lessor shall lease the Satellite to the Lessee.

<PAGE>

         1.2 Term
             ----
             (a) Initial Lease Term. The initial term of the Lease (the "Initial
                 ------------------ 
Lease Term") shall  commence on the Start Date and shall  terminate on the fifth
anniversary of the Start Date, unless this Lease is earlier terminated  pursuant
to Section 5.

             (b) Renewal.  By written notice given no later than the date which 
                 -------
is two years  and  one  hundred  eighty-three  days  after  the Start Date (and 
provided this Lease has not earlier been terminated  pursuant to Section 5), the
Lessee shall have the  right  to  extend  the  term of the  Lease  to the End of
Life of the Satellite (the "Renewal Term"), provided that there is not as of the
giving of such written  notice an Event of Default,  and there is not as of the 
end of the Initial  Lease Term an Event of Default.  The Renewal  Term shall be 
governed by  all of  the  same terms and conditions of this Lease.  "Lease Term"
shall  mean the Initial Term  and, if extended  as provided herein, the Renewal 
Term.

         1.3 Payments From Lessee
             --------------------

             1.3.1(a)  Lease Payments During Lease Term. In consideration of the
                       --------------------------------
lease of the Satellite to the Lessee  during the Initial Term,  the Lessee shall
pay the Lessor an aggregate of One Hundred Ninety Million Dollars ($190,000,000)
consisting   of  annual  Lease   payments  of   Thirty-Eight   Million   Dollars
($38,000,000)  (net of all  taxes,  assessments,  charges,  levies  or duties as
provided in Section  1.3(h) of this Lease).  Lease  payments  shall be deemed to
include payments owed to AMSC as  consideration  for the license of intellectual
property and software  owned by AMSC and licensed to the Lessee  pursuant to the
separate License Agreement being entered into simultaneously herewith.

             1.3.1(b)  Initial  Payment.  On  the Satellite  Contract  Date, the
                       ----------------
Lessee  shall  pay the  initial  Seven  Million  Five  Hundred  Thousand  Dollar
($7,500,000) portion of the Initial Payment to the Lessor, and no later than the
date  forty-five  (45) days after the Satellite  Contract Date, the Lessee shall
pay the remaining Two Million Five Hundred Thousand Dollar ($2,500,000)  portion
of the Initial Payment to the Lessor.

             1.3.1(c)  Post-Offering   Payment.   Within  ten  (10)  days  after
                       -----------------------
successful completion  of  the Offering, the Lessee shall make the Post-Offering
Payment to the Lessor.

             1.3.1(d)  Initial  AMSC Payment  Expenses.  On the Start Date,  the
                       -------------------------------
Lessee shall pay to AMSC an amount  equal to the Initial  AMSC Payment  Expenses
that the Lessee has theretofore  directed to be made by the Lessor, as presented
in writing to the Lessee by AMSC, with such reasonable  backup  documentation as
may be reasonably requested by the Lessee.

<PAGE>

             1.3.1(e)  Treatment of Initial Payment, Post-Offering Payment
                       and Initial AMSC Payment Expenses
                       ---------------------------------------------------

                   (i) Except to the extent another disposition of such  amounts
is provided for in this Lease, the Initial Payment and the Post-Offering Payment
shall be  applied  against  and up to the  amount of future  lease  payments  in
reverse  order from the end of the Lease Term as they are owed  pursuant to this
Lease (if the renewal  option  referred to in Section  1.2(b) is exercised,  the
Initial Payment and the Post-Offering  Payment shall be applied to the last year
of the Renewal Term).

                   (ii) The Initial Payment, the Post-Offering Payment and the 
Initial  AMSC  Payment  Expenses  shall  be  the  property of the Lessor and are
nonrefundable except as provided in Section 5 of this Lease.

             1.3.1(f)  Manner  of  Payment.  Lease  payments  shall  be due and
                       -------------------
payable to the  Lessor  quarterly  in  arrears  on the last day of March,  June,
September  and  December  during the Lease  Term.  The initial  quarterly  Lease
payment and the final  quarterly  Lease payment shall be prorated as appropriate
to reflect the actual number of days in that payment  period,  if such period is
less  than a full  calendar  quarter.  Amounts  due and  payable  to the  Lessor
pursuant  to this  Lease  shall be paid to the  Lessor's  account  in the United
States,  or upon Lessor's  direction to an account in Canada,  and in the manner
provided on Schedule 1.3 or in such other manner as may be designated  from time
            ------------ 
to time by the Lessor.  All  payments  by the Lessee  shall be deemed to be made
only upon receipt of collected funds.

             1.3.1(g)  Late Payment.  Any  payment  due  from  the Lessee to the
                       ------------
Lessor that is not  received  by the Lessor on the date that it  is due shall be
subject to  a  late payment charge at a rate of one percent  (1.0%) per month on
such overdue  amount from the due date until it is actually  received,  provided
that if payment is received within five (5) days of the due date, interest shall
not be due from the Lessee as a result of the late payment.

             1.3.1(h)  Taxes.  The  Lessee shall indemnify and hold harmless the
                       -----
Lessor for any and all taxes,  assessments,  charges, levies or duties ("Taxes")
which may be asserted by any local, state or national  governmental  entity as a
result of the Lease other than any such Taxes imposed on the gross or net income
of the Lessor or Taxes in the nature of franchise or doing  business Taxes which
would not have been imposed on the Lessor but for the  activities of the Lessor,
other than in connection with the Lease,  with the exception of any income taxes
imposed on the Lessor in its home jurisdiction.  The Lessor shall cooperate with
the  Lessee  at  Lessee's  reasonable  request  to make such  filings  as may be
necessary or  appropriate  to recover taxes pursuant to this Section that can be
rebated only to the Lessor or with Lessor's  assistance and upon any such rebate
to the  Lessor  shall  pay over  such  rebate to the  Lessee.  If the  Lessor is
required  by law to pay or pays  any  such  Taxes,  the  Lessee  shall  promptly
reimburse the Lessor for such payments  within thirty (30) days from the date of
Lessor's invoice to the Lessee for same,  provided that the Lessor shall, to the
extent reasonably practicable,  give the Lessee reasonable advance notice of the

<PAGE>

Lessor's  proposed  payment of such Taxes and the Lessee shall have fifteen (15)
days after  receipt of such  notice to give the Lessor  written  notice that the
Lessee  requests  that the Lessor  not pay such claim and that the Lessee  shall
undertake  the  contest  of such Taxes  (with  counsel  subject to the  Lessor's
consent, not to be unreasonably withheld, and with the  Lessor  having the right
to  participate  in such  contest at its own expense)  and shall  indemnify  the
Lessor for any Taxes or other amounts which may be due by the Lessor  (including
amounts due as a result of delay in payment and contest),  provided further that
the Lessee  shall have no such right to require the Lessor not to pay such Taxes
and to assume  control  of the  contest  if the  failure to pay the Taxes and to
contest  involves  any risk of criminal liability to the Lessor or other harm to
the Lessor or the Lessor's  business  which harm to the Lessor it is  reasonably
determined  may  not be  adequately  compensated  for by the  payment  of  money
pursuant  to the  indemnification  provided  in this  Section.  In the event the
Lessor does  business  in Africa  other than in  connection  with this Lease and
transactions  related to this Lease,  and as a result of which conduct  business
Taxes are  imposed on the  Lessor,  the  Lessor,  and not the  Lessee,  shall be
responsible for such Taxes.  Notwithstanding the foregoing, the Lessee shall not
be required to  indemnify  the Lessor for Taxes that would not have been imposed
but for the gross negligence or willful misconduct of the Lessor.

         1.4 Return or Retirement of Satellite
             Upon Expiration of Lease Term
             or Termination of Lease
             ---------------------------------

             1.4.1(a)  Upon the  expiration of the Lease Term,  the Lessor shall
remove the  Satellite  from the  Relocated  Orbital  Position and shall,  at the
option of the Lessor and,  except as provided in this Lease,  at Lessor's  risk,
either  relocate the  Satellite to the Returned  Orbital  Position or retire the
Satellite by removing it from geostationary  orbit;  provided that if at the end
of the Renewal Term, if the relocation or removal of the Satellite  results in a
collision to another  satellite and the Lessee is not at fault,  then the Lessor
shall indemnify the Lessee from any claims with respect to such damage; provided
further that in no event shall the Lessor have any liability to the Lessee,  the
Lessee's customers or suppliers,  or any other person related to the Lessee. The
Lessor  shall have the sole right to  determine  whether the  Satellite is to be
returned or retired,  and shall use its best efforts to notify the Lessee of its
choice nine (9) months  prior to the  expiration  of the Lease Term.  The Lessee
shall be responsible for the costs  associated with the removal or relocation of
the  Satellite  in  an  amount  not  to  exceed  Six  Hundred  Thousand  Dollars
($600,000),  and assuming a rate of drift no slower than one degree of longitude
per day,  provided that Lessee's  responsibility  hereunder shall not exceed one
hundred twenty (120) days at the Lessee's expense.

2.  Steps To Be Taken Before
    Relocation of Satellite
    ------------------------

             2.1 Relocation of Satellite.  The relocation shall be in accordance
                 -----------------------
with the Satellite Relocation Plan attached to this Lease as Schedule  2.1.  The
                                                             -------------
Relocation  Commencement  Date will begin within  twenty-one (21) days after the
Satellite  Relocation  Date,  adjusted for delays not caused by the Lessor.  The
rate of drift of the Satellite  shall be at no more than one degree of longitude
per day.

<PAGE>

             2.2 In-Orbit Insurance.
                 ------------------
 
                 2.2.1(a)   The  Lessor  shall  exercise  reasonable  commercial

efforts  to obtain  in-orbit  insurance  for the  Satellite  from the Start Date
(including  coverage of drift and inversion) on substantially  the terms of, and
at a premium rate not in excess of the premium rate under, the Lessor's in-orbit
insurance  policy in effect for the  Satellite  as of October 4, 1997, a copy of
which shall be delivered to the Lessee in connection  with the execution of this
Lease (with additional endorsements consistent with this Section 2.2 and Article
5) and in the aggregate amount of $150,000,000; provided that the Lessor may for
its own account obtain  insurance in excess of such  $150,000,000,  and provided
further that as of the On Station  Acceptance Date, the Lessor's only obligation
to the Lessee with respect to in-orbit  insurance shall be to maintain insurance
in amounts  for which the  Lessee is to be the  beneficiary  (i.e.,  up to Fifty
Million Dollars ($50,000,000)). The Lessor shall make the Lessee the beneficiary
for one-third of the amount of such  $150,000,000  (if  available) of insurance,
provided  that in the event that a lesser  amount of  insurance  is available on
commercially  reasonable  terms  (including as a result of diminished  insurable
Satellite value over time), the Lessee shall be named  beneficiary for one-third
of such lesser amount. In the event the Lessor determines that insurance on such
terms and such amount is unavailable, the Lessor shall not be required to insure
either its own interest or the Lessee's  interest in the  Satellite.  The Lessee
and the Lessor shall each cooperate and take such actions as may be requested by
the other in connection  with  securing the  insurance  and  complying  with all
insurance  policies secured.  The in-orbit insurance policies shall provide that
to the extent  proceeds  are paid under the policies and the Lessee has breached
policy  requirements  or if an Event of Default under Sections  6(a)(i),  (v) or
(vii) has occurred, the Lessor shall be entitled to the Lessee's interest in the
policy and proceeds thereof, which shall be paid to the Lessor, provided that in
the event of an Event of Default  under Section  6(a)(i) or 6(a)(v),  the Lessor
shall be entitled  only to amounts  owing and remaining to be owed to the Lessor
under or in  connection  with the  remainder  of the Lease.  

                 2.2.1(b)  The  Lessor shall  bear  the  premium and expenses of
insurance on the Lessee's  interest.  

             2.3 Lessee  to  Secure TT&C  Facilities  and Service to Receive and
                 ---------------------------------------------------------------
Operate  Satellite.
- ------------------

                 2.3.1(a)  The Lessee shall design and build TT&C  facilities in
accordance  with the requirements set forth on Schedule 2.3. 
                                               ------------

                 2.3.1(b)  The Lessee  shall  arrange to  obtain  TT&C  Services
from a provider and  pursuant  to terms and  conditions acceptable to the Lessor
to  enable  the  Satellite  to be received and operated at the Relocated Orbital
Position during the Lease Term.

<PAGE>


3.       Obligations and Covenants of Lessee
         -----------------------------------

The  Lessee  hereby  agrees  and  covenants  with  the  Lessor  that  the Lessee
shall faithfully and diligently  perform, at the Lessee's sole cost and expense,
each of the covenants  set forth in this Lease,  including  without  limitation,
those set forth in this Section 3.

         3.1 Enabling  the  Satellite  to Continue to Occupy  Relocated  Orbital
             -------------------------------------------------------------------
Position. The Lessee shall satisfy all Applicable Legal Requirements (other than
- --------
FCC  and  Canadian   government   approvals  and  any  other   Applicable  Legal
Requirements  that the  Lessor is  responsible  for  satisfying)  to enable  the
Satellite to occupy and operate from the Relocated  Orbital Position  throughout
the Lease Term, and shall provide the Lessor with  quarterly  status reports and
evidence as to the Lessee's  satisfaction of such obligation promptly at the end
of each calendar quarter during the Lease Term.

         3.2 Notice of Problems Involving Satellite.  Throughout the Lease Term,
             --------------------------------------
the Lessee shall as promptly as practicable provide written notice to the Lessor
of any performance  problems or anomalies with respect to the Satellite of which
the Lessee is aware.

         3.3 Use of  Fully-Qualified  Personnel.  Throughout the Lease Term, the
             ----------------------------------
Lessee shall permit only  fully-qualified  personnel to operate the Satellite or
be  involved  in  communications  to or from the  Satellite;  for this  purpose,
"fully-qualified   personnel"  shall  be  deemed  to  be  those  personnel  with
substantially  the  level and  quality  of  experience  and  background,  and in
substantially  equivalent  numbers,  as are  employed or under  contract in like
activities  on behalf of the Lessor with  respect to the  Satellite  on the date
hereof and including, without limitation, Telesat personnel.

         3.4 Satellite Operation: Compliance With Specified Operating Procedures
             -------------------------------------------------------------------
and Applicable Legal  Requirements.  Throughout the Lease Term, the Lessee shall
- ----------------------------------
operate the  Satellite  and install,  operate and maintain in good working order
ground  facilities  and  equipment  for  transmitting  signals to, and receiving
signals from, the Satellite  ("Lessee-Provided  Facilities")  in compliance with
all applicable  Satellite operating procedures and operational  limitations,  if
any, issued by the Satellite's  manufacturer and/or  subcontractors,  as well as
Applicable Legal  Requirements now or hereafter existing or arising and pursuant
to such additional  requirements as may be reasonably  directed by the Lessor to
ensure the health and safe operation of the Satellite.

         3.5 TT&C
             ----

             3.5.1(a)  Throughout  the  Lease Term, the Lessee shall maintain or
cause to be maintained  TT&C  facilities  from which to control the operation of
the  Satellite  and  provide  or  cause to be  provided  TT&C  Services  for the
Satellite that are of a quality and level  consistent  with  satellite  industry
standards,  and  consistent  with the terms and  requirements  set forth in this
Lease.

<PAGE>

             3.5.1(b)  Without  limiting the obligation of the Lessee as set out
in Section 3.5(a) above, the Lessee  acknowledges and agrees that the Lessor may
at any time, and from time to time, when the Lessor  determines,  through action
of an  executive  officer of the  Lessor,  that,  absent  such  intervention,  a
reasonable  fully-qualified  person  would  determine  that it is  necessary  or
appropriate for the health or safe operation of the Satellite,  when an Event of
Default has occurred or when this Lease has otherwise terminated, assume control
for  directing  the  activities  of the TT&C  Services  provider  under the TT&C
Services contract with respect to the Satellite,  without incurring liability of
any kind to the Lessee,  except for the  Lessor's  gross  negligence  or willful
misconduct,  it being  agreed  that  actions  taken  under the  direction  of an
executive officer of the Lessor will not constitute gross negligence.  Except in
situations  involving  the  health  or safety  of the  Satellite  or an Event of
Default, Lessor shall endeavor to minimize the adverse impact of such activities
on the Lessee's  business.  For this purpose,  the Lessee hereby irrevocably and
unconditionally  appoints and authorizes the Lessor individually as its attorney
to issue to the Lessee's TT&C  Services  provider (or any successor or assign of
such TT&C Services  provider) any or all commands,  directions and instructions,
and provide all data as is necessary or desirable for the performance of TT&C on
the  Satellite.   The  Lessee  further   acknowledges   and  agrees  to  execute
simultaneously  with the  signing  of this Lease a letter to the  Lessee's  TT&C
Services  provider in form and  substance  satisfactory  to the  Lessor,  acting
reasonably,  which confirms the authority granted to the Lessor pursuant to this
Section  3.5(b).  The obligation to pay the Lessee's TT&C Services  provider for
TT&C Services under the TT&C Services contract (or otherwise) shall at all times
and under all circumstances remain with the Lessee.

         3.6 Frequency Coordination. Throughout the Lease Term, the Lessee shall
             ----------------------
coordinate  electromagnetic  spectrum for the  operation of the Satellite at the
Relocated  Orbital Position and shall satisfy all Applicable Legal  Requirements
and established practices and procedures for such coordination. The Lessor shall
have the right to  monitor  the  coordination  process,  including  the right to
attend  frequency  coordination  meetings  (which shall be at the expense of the
Lessee if, in the Lessee's reasonable  judgment,  such attendance is required by
Applicable Legal Requirements, but otherwise, at the expense of the Lessor). The
Lessee shall provide the Lessor with  quarterly  reports as to the  coordination
process and shall  provide  evidence  reasonably  acceptable  to the Lessor that
Applicable Legal Requirements with respect to coordination have been satisfied.

         3.7 Safe  Operation.  Throughout the Lease Term and until such time (if
             ---------------
any) as the Satellite is removed from the Relocated Orbital Position, the Lessee
shall not operate or use the Satellite or any portion  thereof in a manner which
would or could reasonably be expected to:

                     (i)   damage the Satellite;

                     (ii)  damage  any  other  in-orbit satellite or any portion
                           thereof; or

                     (iii) interfere  with  the  use  or operation  of any other
                           satellite or any portion thereof.

<PAGE>

         3.8  Reporting.  During the Lease Term,  the Lessee  shall  provide the
              ---------
information  described in, and on the  frequency set forth in,  Schedule 3.8, in
                                                                ------------
such form and  specificity as would be standard under similar  circumstances  in
the satellite  industry.  In addition,  during the Lease Term,  the Lessee shall
provide  additional  reports relating to any events or anomalies relating to the
Satellite as may be reasonably necessary or appropriate (i) for the Lessor to
evaluate  whether  performance  incentive  payments  are due to the  Satellite's
manufacturers  with  respect to the  Satellite  and to take action with  respect
thereto,  (ii) for securing and  maintaining  insurance  covering the Satellite,
(iii)  in  connection  with  the  Lessor's  financial  transactions,   reporting
obligations   under  Applicable  Legal   Requirements  and  the  preparation  of
disclosure  documents pursuant to Applicable Legal Requirements,  (iv) to comply
with Applicable Legal Requirements,  and (v) for other reasonable purposes.  The
Lessor  acknowledges  that the Lessee shall not be responsible  for  performance
incentive payments due to the Satellite's manufacturer.

         3.9 Government Approvals For Use of Satellite,  Etc. Except as noted in
             ------------------------------------------------
Section 3.1 about FCC and Canadian government approvals, the Lessee, and not the
Lessor,  shall have  responsibility  for obtaining and maintaining all necessary
approvals of governmental  entities and  international  organizations to use the
Satellite,  including  but  not  limited  to  rights  to the  Relocated  Orbital
Position,  securing rights to use the coordinated L-band and Ku-band frequencies
suitable  for the  Satellite,  and all  approvals  needed  to  operate  the TT&C
facilities  and provide  the TT&C  Services  contemplated  to be provided by the
Lessee  by this  Lease.  The  Lessor  shall  cooperate  with the  Lessee  in all
reasonable respects in Lessee's efforts to secure and maintain such approvals.

         3.10  Additional  Guarantees.  If, in the  opinion of the  Lessor,  the
               ----------------------
additional  financial  assurances of one or more parents or  subsidiaries of the
Lessee are reasonably required,  then upon the request of the Lessor, the Lessee
shall obtain a written  guarantee,  substantially  in the form of the  guarantee
referred to in Section 9 of this Lease, from such parents and/or subsidiaries.

         3.11  Cooperation and Support in Obtaining and  Maintaining  Insurance.
               ----------------------------------------------------------------
The Lessee  shall  cooperate  with the Lessor in the  process of  obtaining  and
maintaining  insurance relating to the Satellite,  including in-orbit insurance.
The Lessee shall  provide the Lessor  access to all  technical  information  and
reports it may have, or may obtain, from Lessee's own technical staff or outside
contractors  which may  reasonably  be required in order to obtain and  maintain
insurance on the most beneficial  terms to the Lessor or the Lessee.  The Lessee
shall also provide the Lessor reasonable access to its satellite technical staff
or  outside  contractors  for  purposes  of  insurance  presentations  or  claim
prosecution.

         3.12 Additional Financial Obligations and Covenants
              ----------------------------------------------

         The Lessee hereby  agrees and  covenants  with the Lessor that it shall
faithfully  and  diligently  perform,  at its  cost  and  expense,  each  of the
covenants set forth in this Section 3.12.

<PAGE>

             3.12.1(a)  Delivery  of Business  Plan. The Lessee shall deliver to
                        ---------------------------
the Lessor on or prior to the date hereof, a copy of the Lessee's final business
plan, which shall address the business of the Lessee and affiliates  through the
end of the Initial Lease Term (the "Business Plan");

             3.12.1(b)  Delivery  of  Financial  Information.  The  Lessee shall
                        ------------------------------------
deliver to the Lessor:

                     (i)  Within  120  days of the end of  each  fiscal  year of
             the Lessee, the  Lessee's annual  audited  consolidated   financial
             statements,   showing  the  consolidated  financial  condition  and
             results of operations of the Lessee and its  Subsidiaries  for such
             fiscal year, prepared in accordance with GAAP and accompanied by an
             unqualified  opinion  thereon  by  a firm  of independent certified
             public accountants;

                     (ii) Within 45 days of the  end of  each  half  year of the
             Lessee's   fiscal  year,  the  unaudited   consolidated   financial
             statements  of  the  Lessee  showing  the  consolidated   financial
             condition   and  results  of  operations  of  the  Lessee  and  its
             Subsidiaries for such half year,  together with a certificate of an
             officer  of the Lessee  that such  financial  statements  have been
             prepared in accordance with GAAP;

                     (iii) Within 30 days of the end of each month, such monthly
             financial  reports  as  are  ordinarily  prepared  for  the  senior
             management  or Boards of  Directors  of the  Lessee  showing  their
             consolidated  financial condition and results of operations for the
             preceding month;

                     (iv) Within  30 days  of  its  adoption, but in any case no
             later  than 30 days  after the start of the Lessee's fiscal year, a
             copy  of  the  annual  consolidated  budget  of  the Lessee and its
             Subsidiaries for such fiscal year; and

                     (v)  Within  10  days  of  their  distribution  to  the 
             stockholders of the  Lessee,  copies  of  any  circulars  or  other
             documents  or information that are distributed by the Lessee to its
             stockholders.

                 3.12.1(c) Actions Requiring Approval of Lessor During Start-up.
                           ----------------------------------------------------
Until Net Services Revenue exceeds the annual Lease payment,  neither the Lessee
nor any  Guarantor  under  Section  9 shall  take any of the  following  actions
without the Lessor's  written  approval in advance,  which approval shall not be
unreasonably withheld:

                     (i) Fund any capital expenditure in excess of Five  Million
             Dollars  related  to any  Second  Generation  Satellite  other than
             through Subsequent Financing;

<PAGE>

                     (ii) Make  an  acquisition  or  investment  with a value in
             excess of  Five  Million  Dollars  in  another  company or business
             (whether by the acquisition of stock or any other interest,  or the
             acquisition of  assets),  or  otherwise  enter  into any  business,
             other  than  as contemplated  by  the  Business  Plan  or  entirely
             through  Subsequent Financing; or

                     (iii) Declare or pay any dividends.

                 3.12.1(d) Other Actions Requiring  Approval of Lessor.  During
                           ------------------------------------------- 
the Term  of  the Lease,  neither the Lessee nor any  Guarantor  under Section 9
shall  take  any  of  the  following  actions  without  the  Lessor's  written  
approval in advance, which approval shall not be unreasonably withheld:

                     (i) Incur any debt  whose obligations  would rank senior to
             the payment obligations of the Lessee pursuant to the Lease; or

                     (ii) Sell,  lease,  transfer  or  otherwise  dispose of any
             assets other than in the ordinary course of business.

                 3.12.1(e) Resolution of Disputes.  The  parties  to this  Lease
                           ----------------------
confirm  that,  in the event of a dispute  over the  applicability  of  Sections
3.12(c) or (d),  including the need for and  reasonableness  of Lessor approval,
the expedited arbitration procedures of Section 13.6 shall be used.

                 3.12.1(f) Escrow  of  Securities.  Immediately  prior  to  the
                           ----------------------
Offering, the Lessee shall cause each of the  officers  and  directors  named in
Schedule 3.12,  as  holders  of the issued and outstanding  shares of the equity
- -------------
securities of the Lessee and any Guarantor,  to place their respective shares of
the Lessee and any Guarantor in escrow with a financial institution and on terms
reasonably acceptable to the Lessor; provided that with respect to each of these
officers and directors:

                     (i) One  half  of  their  shares  of such equity securities
shall be released from escrow on the Release Date; and

                     (ii) All  of  their  remaining  shares  of  such  equity
             securities shall be released one year after the Release Date.

                     (iii) It  is  understood  that  only  shares  issued to the
             named  officers and/or  directors as  of  the Offering date will be
             included  in  this  escrow.  Any  shares  issued  subsequent to the
             Offering  to  one  of the  officers  or  directors  covered by this
             clause  either by purchase or pursuant to an employee  stock option
             plan shall not be covered by this escrow.

                 3.12.1(g) Definitions.   For purposes of this Section 3.12, the
                           -----------
following terms shall have the following meanings:

                 "GAAP"  shall mean  generally  accepted  accounting  principles
                  ----
             consistently applied in the United States.

<PAGE>

                 "Net Services  Revenue" shall mean the amount  recognized under
                  ---------------------
             GAAP  as  revenue  earned  by  the  Lessee  from  the  sale  of the
             Satellite's  services  during the  Lessee's  preceding  four fiscal
             quarters, less any allowance for bad debts. Net Services Revenue as
             defined  herein shall  exclude any revenue,  income or dividends of
             Lessee's  service  providers  even  if  Lessee  has  an  investment
             therein.

                 "Release Date" shall mean the later of the  Commercial  Service
                  ------------
             Date or the first anniversary of the Offering.

                 "Second  Generation  Satellite"  shall mean any satellite other
                  -----------------------------
             than  the  Satellite   that  is  operated  by  the  Lessee  or  its
             Subsidiaries  or that the  Lessee  or its  Subsidiaries  intend  to
             operate.

                 "Subsequent  Financing"  shall  mean debt or  equity  financing
                  ---------------------
             obtained after the Offering.


4.       Other Rights and Obligations of Lessor
         --------------------------------------

         4.1 Rights.  From the date hereof and  throughout  the Lease Term,  the
             ------
Lessor shall have the following specific rights, in addition to any other rights
the Lessor may have under applicable law.

             4.1.1(a) Inspection.  The  Lessor shall have the right, but not the
                      ----------
obligation,  to inspect all TT&C facilities and  Lessee-Provided  Facilities and
associated  facilities and equipment which are used by the Lessee (or by a third
party under the  authority  of the  Lessee) to  transmit  signals to and receive
signals from the Satellite.  Such inspections  shall be at the Lessor's expense,
shall be conducted  during normal business  hours,  and shall be conducted so as
not to unreasonably  interfere with Lessee's business.  The Lessor shall provide
the Lessee reasonable advance notice of such inspections.

              4.1.1(b)  Action  to  Protect  Satellite.   Without  limiting  the
                        ------------------------------
generality  of Section  3.5(b)  above,  if  circumstances  occur  which,  in the
Lessor's  reasonable  judgment,  pose a threat  to the  health  or safety of the
Satellite, the Lessor shall have the right, by direction of an executive officer
of the Lessor,  to take appropriate  action to protect the Satellite,  including
without  limitation  issuing binding  commands,  directions and  instructions to
Lessee's TT&C Services  provider,  and to provide to such TT&C Services provider
all data as necessary to meet any performance  specifications  applicable to the
Satellite  and/or to safeguard the health of the  Satellite,  without the Lessor
incurring any liability to the Lessee,  except for the Lessor's gross negligence
or willful misconduct, it being agreed that actions taken under the direction of
an executive officer of the Lessor will not constitute gross negligence.  To the
extent  reasonably  practicable,  the Lessor shall provide the Lessee with prior
notice of any such action it proposes to take.

<PAGE>

             4.1.1(c)  Testing.  Without  the Lessor incurring  liability to the
                       -------
Lessee, the Lessor shall have the right to suspend Lessee's  communications with
the  Satellite  on such  notice as is  reasonable  under the  circumstances  for
purposes  of testing in  connection  with a failure  or  suspected  failure of a
component or subsystem of the Satellite or in response to an order of a court or
governmental  agency,  or to determine the cause or source of any  interference.
Except in situations involving the health or safety of the Satellite or an Event
of Default,  the Lessor shall  endeavor to minimize  the adverse  impact of such
activities on the Lessee's business.

         4.2 Certain Responsibilities of Lessor.
             ----------------------------------

             4.2.1(a)  Documentation.  The  Lessor shall provide the Lessee with
                       -------------
the documentation it uses to operate the Satellite, subject to applicable export
control and other  Applicable Legal  Requirements,  approvals for which shall be
the responsibility of the Lessor at Lessor's expense.

             4.2.1(b)  Performance  Tests.  The  Lessor shall  perform the North
                       ------------------
American  Performance Tests and the African Performance Tests in accordance with
the Test Plan  included  in  Schedule  2.1 and shall  provide  the Lessee with a
written  report of the results of such  Performance  Tests within  fourteen (14)
days after completion of the applicable Performance Tests.

             4.2.1(c) U.S. and  Canadian Government Approvals For Relocation and
                      ----------------------------------------------------------
Export  of  the  Satellite.   The  Lessor,  and  not  the  Lessee,   shall  have
- --------------------------
responsibility  for obtaining and  maintaining  all necessary  U.S. and Canadian
government  approvals  (including  FCC and  export  control  approvals)  for the
relocation and export of the Satellite to the Relocated  Orbital  Position.  The
Lessee shall  cooperate  with the Lessor and supply such  information  and other
assistance  as the Lessor may  reasonably  request  in the  Lessor's  efforts to
obtain and maintain such approvals.

             4.2.1(d)  Timing  of Delivery of  Satellite.  The Lessor  shall use
                       ---------------------------------
best efforts to deliver the Satellite to the Relocated  Orbital  Position within
twelve  (12) to fifteen  (15)  months  after the Start  Date,  such period to be
adjusted  for delays  not caused by the  Lessor,  including  but not  limited to
regulatory  delays  in  securing  approvals  for  relocation  and  export of the
Satellite  and  delays  due  to  the  Lessee's  failure  to  perform  any of its
obligations under this Lease.


5.       Termination Rights; Effect of Termination; Lease Continuation
         -------------------------------------------------------------

         5.1 Lessee's Right to Terminate in Certain Circumstances
             ----------------------------------------------------

                 (a) The Lessee  shall  have the right to terminate the Lease in
the following circumstances:

                     (i) If the Lessor fails despite its  reasonable  commercial
             efforts to obtain all  necessary  American and Canadian  government
             approvals  or consents to relocate the  Satellite or to  consummate
             the  transactions  contemplated  hereby on or before March 15, 1998
             (attached  to this Lease at Schedule  5.1 is the  Lessor's  current
                                         -------------
             understanding of such approvals and consents); or

<PAGE>

                     (ii) By   written  notice  given  within  seven  (7) days  
             after  receipt  of  the  North  American  Performance  Tests report
             pursuant  to  Section 4.2(b), if  the report  demonstrates that the
             Satellite does not meet the Minimum Performance Specifications; or

                     (iii) If the Lessor suffers a Bankruptcy Event on or before
             the Relocation Commencement Date; or

                     (iv) If  in-orbit  insurance  on  the  terms  set  forth in
             Section 2.2 is not secured by the Start Date.

                 (b) If  the  Lease  is  terminated  pursuant to Section  5.1(a)
above,  the  Lessor  shall  refund to the Lessee the difference  between (i) all
Lease  payments  made  by  the  Lessee, including  the  Initial  Payment and the
Post-Offering Payment, less (x) the  Initial  AMSC  Payment  Expenses  and  CMIS
Expenses,  (y) the unreimbursed  Space  Segment  Expenses,  and  (z)  $5,000,000
in  the  case of  a termination  under  Section  5.1(a)(ii)-(iv),  and  (ii) any
insurance  paid or payable to the Lessee in respect of the event  giving rise to
termination of  the  Lease,  and  all Ground Segment  Contracts  (except for the
License  Agreement  in  accordance  with its terms) to which the Lessor is party
shall automatically and simultaneously  terminate without penalty to the Lessor.
The parties acknowledge  that such amount is a  reasonable  pre-estimate  of the
damages  suffered  by the Lessor or the Lessee, as the case may be, in the event
of such termination,  and  the costs  and expenses incurred by the Lessor or the
Lessee, as the case may be, in pursuing this transaction.

         5.2 Lessor's Right to Terminate in Certain Circumstances
             ----------------------------------------------------

                (a) The Lessor shall  have  the right to terminate  the Lease in
the following circumstances:

                     (i) If  the  Lessor fails despite its reasonable commercial
             efforts  to  obtain all necessary American government  approvals or
             consents to relocate or sell its  interest  in  the   Satellite  or
             to consummate the transactions  contemplated  hereby  on or  before
             April  30,  1998  (attached  to  this Lease at Schedule  5.2 is the
                                                            -------------
             Lessor's  current understanding of such approvals and consents); or

                     (ii) If  the  Lessor  fails  despite  its  reasonable  
             commercial  efforts to obtain all  necessary  Canadian and American
             government approvals or consents  to relocate  the  TMI   Satellite
             or  to  consummate  the  transactions  contemplated by the Purchase
             Agreement  on  or  before April 30, 1998 (attached to this Lease at
             Schedule 5.2  is  the  Lessor's  current  understanding  of  such  
             ------------
             approvals  and consents); or

                     (iii) If  there  is  a  material adverse change  in  the 
             condition of the TMI Satellite prior to the Relocation Commencement
             Date; or

                     (iv) Subject to clause (d) below, if in-orbit  insurance on
             the  terms  set  forth  in  Section 2.2 is not secured by the Start
             Date.

<PAGE>

                 (b) If  the  Lease  is  terminated  pursuant to Section  5.2(a)
above,  the  Lessor shall  refund  to  the  Lessee  the  difference  between (i)
all  Lease  payments  made  by the Lessee, including the Initial Payment and the
Post-Offering  Payment,  less  the  Initial  AMSC  Payment  Expenses  and  CMIS 
Expenses  and  less   the  unreimbursed  Space  Segment  Expenses,  and (ii) any
insurance paid or payable to  Lessee  from  insurance  maintained  by the Lessor
pursuant  to Section  2.2 in  respect of  the event  giving rise to  termination
of  the  Lease,  and  all  Ground Segment  Contracts  (except  for  the  License
Agreement  in  accordance  with its terms)  to which the  Lessor is party  shall
automatically  and  simultaneously terminate without penalty to the Lessor.

                 (c) At  Lessee's  request  and  expense,  the  Lessor shall use
commercially reasonable  efforts to secure  insurance  of up to  $15,000,000  in
favor of  the Lessee  to cover damages  and  loss  associated  with  the  ground
segment portion  of its System  in the event of a material adverse change in the
condition of the TMI Satellite prior to the Relocation Commencement Date.

                 (d) If the Lease is terminated  pursuant to Section 5.2(a)(i), 
(ii) or (iv)  above,  the Lessor  agrees not to sell or lease the  Satellite  to
a third party for one year after such termination.

         5.3 Lessor's Right to Terminate in Certain Additional Circumstances.
             ---------------------------------------------------------------

                 (a) The Lessor shall have the right to terminate  the Lease  in
the following circumstances:

                     (i) If by the date seventy-five (75) days after the date of
             this Lease (A) the Lessee has not  received  and  delivered  to the
             Lessor  formal,  written  permission  from the South Africa Reserve
             Bank to do the Offering on  the  Johannesburg   stock  exchange  or
             (B) a  mutually  acceptable  alternative  Offering  for  which  the
             South  Africa  Reserve Bank approval is not  required is not agreed
             upon between the Lessee and the Lessor;

                     (ii) If the Offering  has not closed on or before the later
             of (A) June 30, 1998 and (B) the  date which is  seventy-five  (75)
             days following  receipt  by the  Lessor of all  necessary  Canadian
             and American government approvals to relocate the Satellite;

                     (iii) If the Post-Offering Payment has not been received on
             or before ten (10) days after the date the Offering closes;

                     (iv) An  Event  of Default occurs and is continuing at the 
             time of termination on or before the Relocation Commencement Date;

                     (v) If the Lessee has not  obtained  final  approval  under
             all Applicable Legal Requirements for the Satellite  to occupy  the
             Relocated Orbital Position,  including  coordination of frequencies
             for TT&C  and  initial  operation,  by April  30,  1998,  provided,
             however,  that in the  event  and to the  extent  that a  delay  in
             obtaining any given approval under an Applicable Legal  Requirement
             occurs  and  such  delay  does  not,  in  the  Lessor's  reasonable
             judgment, unreasonably delay the Lessee's beginning or successfully
             maintaining  commercial service, the Lessor shall not terminate the
             Lease on the basis of such a delay; or

<PAGE>

                     (vi)  If the  Lessee  does  not  have  by  June  1,  1998  
             TT&C  facilities  in  Chilworth operationally complete and ready to
             control  the Satellite, thus ensuring that the Lessee shall be in a
             position to receive and operate the Satellite  upon its  relocation
             by the Lessor to the Relocated Orbital Position.

                 (b) If  the  Lease  is terminated  pursuant  to Section  5.3(a)
above, the Lessor shall be entitled to retain all Lease payments,  including the
Initial  Payment and the  Post-Offering  Payment,  shall retain the Initial AMSC
Payment Expenses and CMIS Expenses and all Ground Segment  Contracts (except for
the License Agreement in accordance with its terms) to which the Lessor is party
shall automatically and simultaneously  terminate without penalty to the Lessor.
The parties  acknowledge  that such amount is a reasonable  pre-estimate  of the
damages  suffered by the Lessor or the Lessee,  as the case may be, in the event
of such  termination,  and the costs and expenses  incurred by the Lessor or the
Lessee, as the case may be, in pursuing this transaction.  The Lessee may retain
all work product funded by the Initial AMSC Payment  Expenses,  if any, which is
not based on or derived  from AMSC owned or  licensed  proprietary  software  or
other  information and consistent with the terms of the License  Agreement;  the
Lessee shall make provision for retention of third-party  work product  directly
with third-party vendors following termination as and if desired.

         5.4 Lessor's and Lessee's Rights to Terminate in
             Event of Total Loss or Constructive Total Loss
             ----------------------------------------------

             (a)  The  Lessor  and  the Lessee  shall each individually have the
right to  terminate  the Lease if, after the Start Date, the Satellite suffers a
Total Loss or Constructive Total Loss.

             (b) If  the  Lease is terminated  pursuant to Section  5.4(a) above
on or after the On  Station  Acceptance  Date,  the  Lessee  shall be  entitled,
subject  to the last  sentence  of Section  2.2(a),  to all  insurance  proceeds
payable to the Lessee in  accordance  with Section  2.2(a)  under the  insurance
policies in respect of such loss, and the Lessor shall retain all Lease payments
made by the Lessee through the termination date,  including the Initial Payment,
the Post-Offering  Payment, the Initial AMSC Payment Expenses and CMIS Expenses,
and all Ground Segment Contracts (except for the License Agreement in accordance
with  its  terms)  to  which  the  Lessor  is  party  shall   automatically  and
simultaneously terminate without penalty to the Lessor.

             (c) I  the Lease  is terminated  pursuant  to Section  5.4(a) above
before the On Station Acceptance Date, the Lessee shall be named in the in-orbit
insurance  policy in Section 2.2 as an additional loss payee for such additional
amount of  insurance  proceeds as  necessary  to enable the Lessee to recover an
amount  equal to all Lease  payments  (but  excluding  any Initial  AMSC Payment
Expenses, CMIS Expenses or Space Segment Expenses) theretofore made.

             (d) If there is a Total Loss  or  Constructive  Total  Loss  of the
Satellite but the Lease is not terminated by either of the Lessor or the Lessee:

                     (i) The  Lease  and  all contracts  relating  to the ground
             segment portion of the system  between  the  Lessor  and the Lessee
             shall remain in force; and

<PAGE>

                     (ii) The  Lessor  shall  pay  to the  Lessee  one-third  of
             all insurance  proceeds paid or payable to the Lessee (with respect
             to the $150,000,000 shared  policy  maximum, or such lesser  amount
             available  under  Section 2.2) (if any) in respect of such loss and
             shall retain all Lease payments, including the Initial Payment, the
             Post-Offering  Payment,  the Initial AMSC Payment Expenses and CMIS
             Expenses; and

                     (iii) The  Lessor  and  the  Lessee  shall  enter into good
             faith  discussions  as to  any appropriate adjustment to the annual
          Lease payment.  If  such  damage  or loss  occurs  prior to  achieving
          the On Station  Acceptance  Date at  expected  performance  levels and
          if the  insurance proceeds received by the Lessee with respect to such
          loss by  the  Lessee  are  not at  least  equal to the Lease  payments
          received by the Lessor to such date, then a retroactive  Lease payment
          adjustment  for  such  difference shall be made, with such retroactive
          adjustment to  be paid to the Lessee equally over the remainder of the
          Lease Term.

         5.5 Lessor's Right to Terminate If Lessee's TT&C Contract 
             -----------------------------------------------------
             Is Not in Place.
             ---------------

                 (a) The  Lessor shall  have the right to terminate the Lease if
the Lessee has  not entered  into an agreement with Telesat with respect to TT&C
services (substantially on the terms proposed by Telesat,  but with the addition
of provisions  relating to the Gibraltar  earth station) for the on-station TT&C
operation  of  the  Satellite  over  or  near  Africa  within forty (40) days of
entering into this Lease.

                 (b) If  the  Lease  is  terminated  pursuant to Section  5.5(a)
above,  the Lessor  shall  refund to the  Lessee  all  Lease  payments  made by 
the  Lessee,  including  the  Initial  Payment  and the Post- Offering  Payment,
less  the  Initial  AMSC  Payment Expenses,  CMIS Expenses,  unreimbursed  Space
Segment Expenses and $1,000,000.

         5.6 Lease  Continuation in Less Than Total or Constructive  Total Loss.
             ------------------------------------------------------------------ 
If, after the Start Date, the Satellite  suffers damage or a loss of performance
(as determined  under a mutually-  agreed method but excluding  normal  in-orbit
deterioration)  during the Lease Term,  and if the damage or loss of performance
is not a Total Loss or Constructive Total Loss, then:

                     (i)  the  Lease,  the  Service  Contract  and  the  License
             Agreement shall remain in force;

                     (ii)  the  Lessor  shall  pay to the  Lessee  one-third  of
             all insurance proceeds  paid or payable to the Lessee (with respect
             to the $150,000,000 shared policy  maximum, or such lesser  amount
             available  under  Section  2.2) (if any) in  respect  of such loss,
             shall retain all Lease payments, including the Initial Payment, the
             Post-Offering  Payment,  the Initial AMSC Payment  Expenses and the
             CMIS Expenses; and

<PAGE>

                     (iii)  the  Lessor and the  Lessee  shall  enter  into good
             faith discussions  as  to  an  appropriate  adjustment,  if any, to
             the annual Lease payment.   If  such  damage or loss of performance
             occurs prior to On Station Acceptance, any Lease payment adjustment
             shall be  retroactive  with respect to Lease payments already made,
             with such  retroactive  adjustment  to be paid to the Lessee by way
             of a credit  prorated  equally against the quarterly Lease payments
             to be  made by  the Lessee to  the Lessor over the remainder of the
             Lease Term.

6.       Events of Default; Remedies
         ---------------------------

             (a) Events of Default.  If one or more of the following  events of 
                 -----------------
default (each  an "Event of Default")  occurs  and  is  continuing,  the Lessors
shall be entitled to the remedies set forth in Section 6(b):

                     (i) Any amount payable by the Lessee hereunder is not  paid
             as and when it becomes  payable within ten (10) days after  notice
             to the Lessee;

                     (ii) The  Lessee  or  any  Guarantor  fails  to  perform or
             observe any  covenant  or agreement to  be performed or observed by
             it, where such  failure  could  reasonably  pose  a  not immaterial
             risk  to  the  health  or  safe  operation  of the Satellite,  and 
             does not remedy  such  failure  (or  otherwise remove such risk, in
             which case the terms of paragraph (iii) of  this Section 6(a) shall
             apply) on  or  before  the  fifth (5th) day  after  written  notice
             thereof is given by the Lessor to the Lessee;

                     (iii) The  Lessee  or  any  Guarantor  fails  to perform or
             observe  any  material  covenant  or  agreement  to be performed or
             observed by it (other than those  referred  to in Section 6(a)(i), 
             6(a)(ii), 6(a)(iv), 6(a)(v) or 6(a)(vi))  and does not  remedy  the
             failure on or before the thirtieth  (30th) day after written notice
             thereof is given by the Lessor to the Lessee;

                     (iv)  Any  material  representation  or  warranty  of  the
             Lessee  or any  Guarantor  in  this  Lease  or  any other  document
             delivered  in  connection  with  this  Lease  proves  to  have been
             incorrect,  incomplete or  misleading in  any  material  respect at
             the  time it  was  made or  repeated  or  deemed  to have been made
             or repeated,  and  shall  not  have  been  remedied  within  thirty
             (30) days thereafter;

                     (v)  If an Event of  Bankruptcy  shall  occur  with respect
             to the Lessee or a Guarantor;

                     (vi) A failure by the Lessee to provide a certificate
             in the form of  Exhibit B to the Lessor  within  (5)  business days
                             ---------
             following  receipt  of  Lessor's  written  request  prior  to  the
             Satellite Relocation Date; and

<PAGE>

                     (vii) a breach or default by the Lessee under Section 3.2,
             3.3, 3.4, 3.5(a), 3.7 or 3.8 of this  Lease  and  such  breach or
             default  is  a  direct  cause  of a  loss  with  respect  to  the
             Satellite.  (For  purposes of this Section 6(a)(vii), "loss"  means
             any loss for which  proceeds  would be payable under  the insurance
             policy  procured  under  Section  2.2 or if no such  policy  is  in
             place,  then  a  loss for which proceeds would be payable under the
             policy referred to in Section 2.2.)  Notwithstanding the foregoing,
             in  the  event  of  a  breach  or  default  that  would  otherwise 
             constitute  an  Event  of  Default under  this  Section  6(a)(vii),
             but  (A)  the  loss  of  the  Satellite is a Partial Loss,  (B) the
             Lessor shall receive the  insurance  proceeds  called for  pursuant
             to  Section  2.2  or  an  equivalent  amount  and  (C)  there is no
             reduction  of  the Lease  payments  under  Section 5.6,  then there
             shall be no Event of Default.

             (b) Remedies.  If  one  or  more  Events  of  Default occurs and is
                 --------
continuing, the Lessor shall be entitled to:

                     (i)  retain  all  amounts  paid to the  Lessor  and  retain
             any insurance  proceeds  with  respect to insurance  maintained  by
             the Lessor  pursuant  to, and to the extent  provided  in,  Section
             2.2 otherwise payable to the Lessee;

                     (ii) exercise its rights under any cross-default provisions
             under the Ground Segment  Contracts,  any credit support agreements
             and other credit assurance mechanisms for any amounts owed to them,
             and to recover expenses and damages;

                     (iii) sell  or  lease  the  Satellite  to  another customer
             and/or remove the  Satellite  from the Relocated  Orbital  Position
             at the Lessee's expense (whether or not resold or released); and

                     (iv) any other remedy available to Lessor under applicable
             law.

         The Lessor shall use  commercially  reasonable  efforts to mitigate its
damages in the exercise of its remedies under this Section 6(b).


7.       Limitation of Liability
         and Indemnification
         -----------------------

         7.1  Limitation  on Lessor's  Liability.  It is expressly  agreed that,
              ----------------------------------
except  with  respect  to acts or  omissions  of the Lessor  constituting  gross
negligence or willful  misconduct,  the sole  obligations and liabilities of the
Lessor, and the exclusive remedies of the Lessee in relation to anything arising
out of the Lease,  including without limitation Total Loss or Constructive Total
Loss of the  Satellite,  Partial  Loss of the  Satellite,  or any other  problem
associated  with the  Satellite  (whether  the basis of  liability  is breach of
contract,  tort  (including  negligence and strict  liability)  statute or other
legal  theory) are limited to those  specified in Sections 2.1, 4, 5, 6 and this
Section 7 and all other remedies of any kind are expressly waived by the Lessee.

<PAGE>

         7.2 Lessee's Indemnification of Lessor
             ----------------------------------

             7.2.1(a) The Lessee shall  indemnify and hold harmless the Lessor,
AMSC, their  respective  Affiliates and their  respective  directors,  officers,
employees,  agents,  shareholders,  partners and subcontractors  (the Lessor and
each  such  other  person,  an  "Indemnified  Party")  from any and all  claims,
liabilities,  losses, costs, or damages,  including attorneys' fees and costs of
investigation, incurred or suffered by any of them arising out of:

                     (i) any claims asserted  against any  Indemnified  Party by
             third  parties  arising out of activities of the Lessee or Lessee's
             Agents or  any  violations  of  Applicable  Legal  Requirements  by
             the Lessee or Lessee's Agents (except to the extent arising out of 
             activities of the Lessor or Lessor's Agents in breach of this Lease
             and any  violations  of Applicable Legal Requirements by the Lessor
             or Lessor's Agents);

                     (ii) any  third-party  claim  asserted  by  any customer or
             supplier of the  Lessee,  which  claim  purportedly  arises  out of
             any  act  or  omission  of any Indemnified Party in connection with
             goods or services  provided, in the case of a customer, by, and in 
             the  case  of  a  supplier,  to,  the  Lessee  unless  such acts or
             omissions are in breach of this Lease;

                     (iii) any  other  third  party  claims   asserted   against
             any  Indemnified  Party  in  connection  with  a   contract  or  
             relationship  between  the Lessee or any of its related parties and
             such third party, except to the  extent caused by acts or omissions
             of the Lessor;

                     (iv) the lease of the Satellite to the Lessee; or

                     (v) TT&C activities provided by or on behalf of the Lessee.

             7.2.1(b)  The  Lessee  shall,  in  each of its  contracts  with its
suppliers, customers,  resellers,  distributors or other vendors of its services
(in  this  Section  7.2(b),  referred  to as "the  Party  Contracting  with  the
Lessee"), insert a provision which reads substantially as follows:

               "AMSC Subsidiary Corporation ('AMSC') and each of its affiliates,
               officers,   directors,   employees,    shareholders,    partners,
               investors, agents and subcontractors shall not be liable, for any
               reason whatsoever, to [the Party Contracting with the Lessee], or
               any   of  its   affiliates,   officers,   directors,   employees,
               shareholders,  partners, investors, agents or subcontractors, for
               losses, damages,  costs, expenses,  liabilities or claims arising
               out of:

                     "(i) the ownership of the Satellite by AMSC or any of  its 
               successors and assigns;

<PAGE>

                     "(ii) the  provision  of any goods or  services by African 
               Continental  Telecommunications  Ltd.,  or  its  successors  and 
               assigns to [the Party Contracting with the Lessee];

                     "(iii) any  failure  of  performance  of  the  Satellite, 
               including without limitation  delays,    in-service interruption,
               degradation or loss or distortion of services."

             7.2.1(c)  Promptly  after  knowledge  of  any  indemnifiable  claim
hereunder, any affected Indemnified Party shall notify the Lessee in writing and
specify  the amount and nature of such claim.  If within  thirty (30) days after
receipt of such notice the Lessee gives such  Indemnified  Party written  notice
that (i) the Lessee intends to defend  against such claim,  at the sole cost and
expense of the Lessee, and (ii) the Lessee  acknowledges that it is obligated to
provide  indemnification  to the Indemnified Party for such claim, then (so long
as  such  matter  does  not  involve  any  risk  of  criminal  liability  to the
Indemnified  Party,  the loss of the Satellite by the Lessor or material risk to
the Satellite, the potential loss of Lessor's principal FCC license(s), or other
harm to the Indemnified  Party (including with respect to intellectual  property
rights of the Lessor or AMSC) or the  Indemnified  Party's  business,  including
matters  relating to claims by government  agencies with  jurisdiction  over the
Indemnified  Party or by AMSC's  shareholders  and which harm to the Indemnified
Party  reasonably  may not be  adequately  compensated  by the  payment of money
pursuant to the indemnification  provided in this Section),  the defense of such
claim shall be by the Lessee (with counsel subject to the Lessor's consent,  not
to be unreasonably  withheld and with the Indemnified  Party having the right to
participate in the defense at its own expense) and the  Indemnified  Party shall
make no payment on such claim so long as the Lessee is  conducting  a good faith
and diligent defense.  Notwithstanding the foregoing,  the Indemnified Party may
take such actions as it  determines  are  reasonable  or necessary  prior to the
expiration  of such thirty  (30) day period in order to protect  its rights.  In
furtherance of the foregoing,  the parties agree to cooperate with each other in
the defense of any such  indemnifiable  claim. If an Indemnified Party elects to
conduct its own defense,  the Lessee may  participate  in the defense at its own
expense,  provided  that the Lessee  shall  nevertheless  remain  liable for all
costs,  expenses,  liabilities and damages  incurred by such  Indemnified  Party
resulting from or arising out of such proceedings or investigations.

         7.3 No  Consequential,  Etc. Damages.  In  no  event  shall (i)  any 
             --------------------------------
Indemnified Party be liable, directly or indirectly,  to the Lessee, or (ii) the
Lessee be liable, directly or indirectly,  to the Lessor, any direct or indirect
users of the  Satellite  or any other  person  for any loss of  profit,  loss of
business, special, indirect, direct, incidental or consequential damages or loss
of revenues arising out of this Lease.

         7.4 Employees of Lessor. Every right, exemption from liability, defense
             -------------------
and immunity of  whatsoever  nature  applicable  to the Lessor or to which it is
entitled  shall  extend to protect  every  employee of the Lessor  acting in the
course of, or in connection with, this Lease.


<PAGE>

8.       Subordination and Assignment
         ----------------------------

         8.1 Security Interests and Secured Parties
             --------------------------------------

             8.1.1(a)  The Lessee  hereby  acknowledges  that this Lease and all
rights granted to the Lessee  hereunder are subject and  subordinate to (without
the necessity of having further  instruments  executed on the part of the Lessee
to effectuate such  subordination)  all security interests and liens whether now
existing or hereafter  created  granted  heretofore or from time to time granted
hereafter  by the Lessor  (collectively,  "Security  Interest")  in favor of its
creditors  (the  "Secured  Parties")  in  and to the  Lessor's  interest  in the
Satellite, this Lease, the proceeds of this Lease, the proceeds from the sale or
other  disposition of all or any portion of the Satellite or this Lease,  or any
insurance  proceeds  that may be paid or  payable to the Lessor in regard to the
Satellite.  The Security Interest shall be deemed to include interests under all
security  agreements,   indentures,   mortgages,  pledge  agreements  and  other
collateral  documents  running  in  favor  of  Secured  Parties,  including  all
renewals,  modifications,  consolidations or replacements thereto  (collectively
the "Collateral Documents").
     -------------------- 

Notwithstanding  the  existence  of  any Security  Interests,  the Lessee shall
continue to have the benefits of this Lease  notwithstanding  any default on the
part of the Lessor under any of the Collateral Documents, so long as no Event of
Default shall have occurred under the Lease.

             8.1.1(b)  Upon  exercise  by any Secured Party of any of its rights
and remedies  under the Security  Interests  granted in its favor and receipt by
the Lessee of notice from any Secured Party of a default by the Lessor under the
Collateral  Documents,  the Lessee shall attorn,  as the Lessee, to such Secured
Party,  as  lessor,  upon all the  terms of this  Lease  (including  making  all
payments which are then, or may thereafter become, due and owing hereunder after
such notice in the manner instructed by such Secured Party(ies)),  provided that
any successor to the Lessor under this Lease

                     (i) expressly  assumes  the  Lessor's obligations hereunder
             for the benefit of the Lessee; and

                     (ii) succeeds  to  substantially  all of  the right, title,
             and  interest  in  and  to all  assets  of the  Lessor   reasonably
             necessary  for  such  successor  to  perform  its obligations under
             this Lease.

Upon any  subsequent  succession  and  assumption of this Lease by a party other
than a Secured  Party,  such  Secured  Party shall be released  from any further
obligations and liabilities under this Lease.

             8.1.1(c)  The  Secured  Parties of the Lessor  shall be entitled to
exercise  all rights and to cure any  defaults  of the Lessor  under this Lease,
within such cure period as may be available to the Lessor under this Lease. Upon
receipt of notice from any  Secured  Parties,  the Lessee  agrees to accept such
exercise and cure by such  Secured  Parties and to render all or any part of the
performance  due to the  Lessor by the Lessee  under this Lease to such  Secured
Parties.

<PAGE>

             8.1.1(d)  Each  Secured  Party  of the  Lessor  shall be  deemed an
express  third-party   beneficiary  of  this  Section.  This  Section  shall  be
self-operative,  and no further instrument of subordination shall be required by
any security  agreement or other document  reflecting any Security  Interests to
make  this  subordination   effective.  In  confirmation  of  such  acknowledged
subordination,  the Lessee shall execute  promptly any instrument or certificate
which the Lessor or its Secured Parties may reasonably request.

         8.2  Lessor's  Right To Assign.  The Lessee  agrees that the Lessor may
              -------------------------
assign its rights and interests under this Lease, in the Satellite and/or in any
or all sums due or to become due to the Lessor  under this Lease to any party at
any time and for any reason,  provided that, except with respect to the granting
of a security  interest or the  assignment of a right to payment,  such assignee
agrees in writing to assume all of the duties and  obligations  hereunder of the
Lessor.

The Lessee  agrees that upon  receipt of notice of such  assignment,  the Lessee
shall  perform all of its  obligations  directly for the benefit of the assignee
and  shall  pay all sums due or to  become  due to the  Lessor  directly  to the
assignee,  or as otherwise directed by such assignee.  Upon receipt of notice of
such assignment,  the Lessee agrees to execute and deliver such documentation as
assignee may reasonably  require from the Lessee to give effect to the intent of
this  Section.  Upon any such  assignment  by the  Lessor,  the Lessor  shall be
released from any further obligations and liabilities under this Lease.

         8.3  Lessee  Assignment.  The  Lessee  shall not  Assign  the  Lessee's
              ------------------
interest in the Satellite or the Lease without the prior written  consent of the
Lessor.  Such  consent  may be  granted  or  withheld  in the sole and  absolute
discretion  of the Lessor if the  assignment is a person other than an affiliate
of the Lessee,  but shall not be unreasonably  withheld if such assignment is to
an affiliate of Lessee. Notwithstanding the foregoing, the Lessee may assign its
rights  and  interests  under  this Lease to a  wholly-owned  subsidiary  of the
Lessee,  provided that such assignee  assumes all of the duties and  obligations
hereunder of the Lessee and executes  such other  instruments  as the Lessor may
reasonably   request,   including,   without   limitation,   instruments  making
representations  and  warranties  made by the  Lessee  in this  Lease,  all such
assumption and other  instruments  and documents to be by written  instrument in
form and  substance  satisfactory  to the Lessor,  and the Lessee  executes  the
Guarantee and other instruments  contemplated by Section 9 of this Lease. If the
Lessor is unable to regain the use of all or any part of the Satellite  free and
clear of any  claims or liens  arising  by or  through  the  Lessee  (including,
without  limitation,  the  Lessee's  subcontractors,   customers,  creditors  or
vendors),  then,  in addition  to any other  remedies  the Lessor may have,  the
Lessee  shall  indemnify  and hold  harmless  the Lessor from any such claims or
liens and, at the Lessor's option,

                     (i)  the  Lessor  may  elect  not  to  regain  use  of  the
             Satellite and the Lessee shall be obligated,  without regard to any
             such termination or expiration of this Lease, to pay the Lessor the
             Lease  payments  due to it at the  rate  specified  herein  for the
             period of time that the Satellite remains so encumbered; or

<PAGE>

                     (ii)  the  Lessor  may  elect  to  regain  such  use of the
             Satellite as it can, and the Lessee shall make such payments to the
             Lessor as shall be necessary to make the Lessor whole for such lost
             use of the Satellite.


9.       Guarantee of Lessee's Obligations
         ---------------------------------

Upon any  permitted  assignment  of this Lease by the  Lessee to a  wholly-owned
subsidiary  of the Lessee  pursuant to Section  8.3,  the Lessee  shall become a
guarantor  of its  successor  Lessee's  obligations  under  this Lease and shall
simultaneously  with such assignment execute a Guarantee in the form attached to
this Lease as  Exhibit  C, and shall  execute  such  other  documents  as may be
               ----------
reasonably requested by the Lessor.


10.      Representations and Warranties of AMSC and AMSC Parent
         ------------------------------------------------------

         10.1 AMSC. AMSC hereby represents and warrants to the Lessee:
              ----

              10.1.1(a)  that  it  is  a  corporation  duly  organized,  validly
existing and in good standing under the laws of the State of Delaware, with full
corporate power, right and authority to execute and to deliver this Lease and to
enter into and to consummate the transactions contemplated hereby;

              10.1.1(b)  that the  execution  and  delivery of this Lease by the
officer so doing, and the consummation of the transactions  contemplated hereby,
have been duly authorized by all necessary corporate action on the part of AMSC;

              10.1.1(c)  that  this  Lease is a valid and binding obligation of 
AMSC, enforceable against AMSC in accordance with its terms;

              10.1.1(d)  that,  subject to  obtaining  the consents or approvals
listed on Schedule 10.1, the execution,  delivery and  performance of this Lease
          -------------
and  the  consummation  of  the  transactions   contemplated  hereby  shall  not
constitute  a  breach,  violation  or  default  of (i)  any  material  contract,
indenture, deed of trust, loan, note, lease, service agreement or other material
instrument  to  which  AMSC is  subject  or is a party;  or (ii) any law,  rule,
regulation,  ordinance,  judgment, decree, order, governmental permit or license
to which AMSC is subject; and

              10.1.1(e)  AMSC  holds  title  to  and  is  the  sole owner of the
Satellite.

         10.2 AMSC Parent.   AMSC  Parent hereby  represents and warrants to the
              -----------
Lessee:

              10.2.1(a)  that  it  is  a  corporation  duly  organized,  validly
existing and  in  good  standing  under the laws of the State of Delaware,  with
full corporate power, right and authority  to execute and to deliver this Lease 
and to enter into and to consummate the transactions contemplated hereby;

              10.2.1(b)  that the  execution  and  delivery of this Lease by the
officer so doing, and the consummation of the transactions  contemplated hereby,
have been duly authorized by all necessary  corporate action on the part of AMSC
Parent;

<PAGE>

              10.2.1(c)  that  this  Lease  is a valid and binding obligation of
AMSC Parent, enforceable against AMSC Parent in accordance with its terms; and

              10.2.1(d)  that,  subject to  obtaining  the consents or approvals
listed on Schedule 10.2, the execution,  delivery and  performance of this Lease
          -------------
and  the  consummation  of  the  transactions   contemplated  hereby  shall  not
constitute  a  breach,  violation  or  default  of (i)  any  material  contract,
indenture, deed of trust, loan, note, lease, service agreement or other material
instrument to which AMSC Parent is subject or is a party; or (ii) any law, rule,
regulation,  ordinance,  judgment, decree, order, governmental permit or license
to which AMSC Parent is subject.


11.      No Warranties and Representations
         Relating to the Satellite
         ---------------------------------

         11.1 No Warranties.  THE LESSEE HEREBY ACKNOWLEDGES THAT THE SATELLITE 
              -------------
WAS CONSTRUCTED, MANUFACTURED AND LAUNCHED BY PERSONS OTHER THAN AMSC, THAT THE 
LESSEE WILL BE PROVIDED WITH THE RESULTS OF CERTAIN PERFORMANCE TESTS, AND THAT 
THE LESSEE HAS BEEN GRANTED  CERTAIN  RIGHTS OF TERMINATION HEREIN IN THE EVENT 
THAT  THE  SATELLITE  DOES  NOT  MEET  THE  SPECIFIED  SATELLITE  PERFORMANCE.  
ACCORDINGLY,  THE  LESSEE  HEREBY  ACKNOWLEDGES  THAT  THE  WARRANTIES  AND  
REPRESENTATIONS  OF AMSC CONTAINED IN SECTION 10 CONSTITUTE THE SOLE  WARRANTIES
AND  REPRESENTATIONS  OF THE LESSOR.  WITHOUT  LIMITING  THE  GENERALITY  OF THE
FOREGOING,  ANY  AND  ALL  EXPRESS  AND  IMPLIED  WARRANTIES WITH RESPECT TO THE
SATELLITE,  INCLUDING,  BUT  NOT  LIMITED  TO,  WARRANTIES  AS  TO  SATELLITE 
PERFORMANCE,  DESIRABILITY,  RELIABILITY, MERCHANTABILITY  OR  FITNESS  FOR  ANY
PURPOSE OR USE OR WARRANTIES AGAINST INTERFERENCE OR INFRINGEMENT, ARE EXPRESSLY
EXCLUDED AND  DISCLAIMED BY THE LESSOR.


12.      Representations and Warranties of Lessee
         ----------------------------------------

         12.1 Lessee.  The Lessee hereby represents and warrants to the Lessor:
              ------

              12.1.1(a) that the Lessee is a corporation duly organized, validly
existing and in good standing  under the laws of Gibraltar,  with full corporate
power,  right and  authority  to execute and to deliver  this Lease and to enter
into and to consummate the transactions contemplated hereby;

              12.1.1(b)  that the  execution  and  delivery of this Lease by the
officer so doing, and the consummation of the transactions  contemplated hereby,
have been duly authorized by all necessary  corporate  action on the part of the
Lessee;

              12.1.1(c) that this Lease is a valid and binding obligation of the
Lessee, enforceable against the Lessee in accordance with its terms; and

<PAGE>

              12.1.1(d)  that,  subject to  obtaining  the consents or approvals
listed on Schedule  12.1(d),  the  execution,  delivery and  performance of this
          -----------------
Lease and the  consummation of the  transactions  contemplated  hereby shall not
constitute  a  breach,  violation  or  default  of (i)  any  material  contract,
indenture,  deed of  trust,  loan,  note,  lease,  service  agreement  or  other
instrument to which the Lessee is subject or is a party;  or (ii) any law, rule,
regulation,  ordinance,  judgment, decree, order, governmental permit or license
to which the Lessee is subject.

              12.1.1(e) the Founders and their ownership interests are set forth
on Schedule 12.1(e).


13.      General Provisions

         13.1 Binding  Effect.  All the terms and provisions of this Lease shall
              ---------------
be  binding  upon and  shall  inure to the  benefit  of (i) the  Lessor  and its
successors  and  permitted  assigns;  (ii) AMSC  Parent and its  successors  and
permitted  assigns;  (iii) the Lessee and its successors and permitted  assigns;
and (iv) any Guarantor and its successors and permitted assigns.

         13.2 Third-Party Rights;  Relationship of Parties.  Except as expressly
              --------------------------------------------
provided  in this  Lease,  nothing  contained  in this Lease  shall be deemed or
construed by the parties or by any third party to create any rights, obligations
or interests of third parties.  Nothing in this Lease is intended to or shall be
construed to create the  relationship  of principal  and agent,  partnership  or
joint venture, or any other fiduciary relationship or association between any of
the parties.

         13.3 Notices.  All notices,  requests and other  communications  to any
              -------
party shall be in writing  (including  telecopy or similar writing) and shall be
given as follows:

             If to the Lessor, to:
                      AMSC Subsidiary Corporation
                      10802 Parkridge Boulevard
                      Reston, Virginia  20191-5416
                      Attention:  General Counsel
                      Fax:  703-758-6134

                                and

                      American Mobile Satellite Corporation
                      10802 Parkridge Boulevard
                      Reston, Virginia  20191-5416
                      Attention:  General Counsel
                      Fax:  703-758-6134

                      with a copy to:

                      AMSC Subsidiary Corporation
                      10802 Parkridge Boulevard
                      Reston, Virginia  20191-5416
                      Attention:  Chief Executive Officer
                      Fax:  703-758-6106

                                and

<PAGE>

                      American Mobile Satellite Corporation
                      10802 Parkridge Boulevard
                      Reston, Virginia  20191-5416
                      Attention:  Chief Executive Officer
                      Fax:  703-758-6106

                      If related to payments, with a copy to
                      the attention of:  Accounting Department



     If to the Lessee, to:
                      African Continental Telecommunications Ltd.
                      57/63 Line Wall Road
                      Gibraltar
                      Attention:  C. Paul Dollery

             with a copy to:

                      Paul, Hastings, Janofsky & Walker LLP
                      Attention:  Joel Simon
                      399 Park Avenue, 31st Floor
                      New York, New York  10022-4697

or to such  other  address  or  telecopier  number as such  party may  hereafter
specify  for the  giving  of  notice.  All  such  notices,  requests  and  other
communications  shall be deemed received on the date of receipt by the recipient
thereof if received prior to 5:00 p.m. in the place of receipt and such day is a
business day in the place of receipt. Otherwise, any such notice, request or
communication  shall  be  deemed  not to  have  been  received  until  the  next
succeeding business day in the place of receipt.

         13.4 Waiver of Breach/Remedies.  No failure on the part of any party to
              -------------------------
notify any other parties of any noncompliance  hereunder,  and no failure on the
part of any party to exercise its rights  hereunder  shall  prejudice any remedy
for any subsequent  noncompliance,  and any waiver by any party or any breach or
noncompliance  with any term or  condition of this Lease shall be limited to the
particular party and the particular  instance and shall not operate or be deemed
to waive any future breaches or noncompliance with any term or condition. Except
as provided herein, all remedies and rights hereunder and those available in law
or in equity shall be cumulative and the exercise by any party of any such right
or remedy  shall not  preclude  the  exercise  of (a) any other  right or remedy
available  to it under this Lease or in law or in equity or (b) the  exercise by
any other  party of any right or remedy  available  to it under this Lease or in
law or in equity.

<PAGE>

         13.5 Applicable  Law.  This Lease shall be  construed  and enforced in
              ---------------
accordance  with the internal  laws of the State of Delaware,  United  States of
America, without regard to the conflict or choice of laws provisions thereof. On
or prior to the  Relocation  Commencement  Date,  the parties  will enter into a
choice of law agreement substantially in the form of Exhibit D hereto.

         13.6 Dispute Resolution
              ------------------

              13.6.1(a) All  controversies  or claims arising out of or relating
to this Lease,  or breach thereof (a "Dispute"),  between the Lessor and/or AMSC
Parent on the one hand and the Lessee and/or a Guarantor on the other hand shall
be resolved in accordance with the procedures set forth in this Section 13.6.

              13.6.1(b)  Initially,  the  Dispute  shall be  referred by written
notice to the Lessee  employee  designated by the Lessee and the Lessor employee
designated by the Lessor to initially review  Disputes.  Disputes related to the
health or safety of the  Satellite  shall be submitted by written  notice to the
Technical Operations Committee.

              13.6.1(c) If within  fifteen (15) days after written notice of the
Dispute is given to them,  the employees to whom the Dispute has been  referred,
or the  Technical  Operations  Committee in the event of Disputes  involving the
health or safety of the Satellite,  do not resolve the Dispute, then the Dispute
shall be  referred  by the  party  asserting  such  Dispute  by  written  notice
delivered to the Chief  Executive  Officer of each of the Lessor and the Lessee,
who shall  attempt,  in good faith,  to resolve the Dispute  within fifteen (15)
days after written notice of such Dispute is given to them.  Such written notice
shall  contain a  statement  setting  forth the  nature of the  Dispute.  At the
request of either the Lessor or the Lessee,  the Chief Executive  Officers shall
meet at the same  location to discuss such  Dispute in good faith.  If the Chief
Executive  Officers are unable to reach  agreement to resolve the Dispute within
the fifteen  (15) day period  after  written  notice of such Dispute is given to
them, the Dispute may be submitted by either party to  arbitration  administered
by  the  American  Arbitration   Association  ("AAA")  in  accordance  with  the
provisions   governing  expedited   arbitration   contained  in  the  Commercial
Arbitration  Rules of the AAA.  The place of  arbitration  shall be  Wilmington,
Delaware.  Any arbitral award shall be in writing and shall be final and binding
on the parties to such arbitration proceeding. The award may include an award of
costs,  including  reasonable  attorneys'  fees and  disbursements,  but may not
include an award of punitive damages.  Judgment upon the award may be entered by
any court having jurisdiction thereof or having jurisdiction over the parties to
such arbitration proceeding or their assets.

         13.7 Counterparts and Formal Date. This Lease may be executed in one or
              ---------------------------- 
more  counterparts,  each of which  when so  executed  shall be  deemed to be an
original  and  such  counterparts  together  shall  constitute  one and the same
instrument  and  notwithstanding  the date(s) of execution by any of the parties
shall be deemed to bear the date written at the beginning of this Lease.

<PAGE>

         13.8 Captions.  The  captions  and  headings  herein are  inserted for
              --------
convenience  and  reference  only and in no way  define  or limit  the  scope or
content of this Lease or in any way affect its provisions.

         13.9 Entire  Understanding.  This Lease,  including  all  exhibits  and
              ---------------------
schedules,  represents the entire  understanding and agreement among the parties
with respect to the subject matter hereof, and supersedes all prior negotiations
and agreements between or among the parties concerning that subject matter. This
Lease may be amended,  supplemented  or changed  only by an agreement in writing
which makes  specific  reference to this Lease and which is signed by the Lessor
and the Lessee and,  with respect to Sections 9 and 13.12,  additionally  by the
Guarantor and AMSC Parent, respectively.

         13.10 Dollar Amounts.   All  references  herein  to  dollar amounts are
               --------------
expressed in U.S. dollars.

         13.11 Lessee's  Payment   Obligations.   The  Lessee's  Lease  payment
               -------------------------------
obligations  are absolute and are not subject to abatement,  reduction or setoff
by reason of any  obligations  of the Lessor to the  Lessee  under this Lease or
otherwise,  except that the Lessee's Lease payment  obligations shall be set off
(i) to the  extent of the cost of such  insurance,  if the Lessor  breaches  its
obligation to secure in-orbit  insurance  pursuant to Section 2.2 and the Lessee
procures  such  insurance,  (ii) to the extent the Lessor is liable for and does
not  satisfy a  monetary  judgment  owed to the  Lessee  under this Lease or the
Service Contract or the License Agreement  pursuant to a final and binding order
pursuant to Section 13.6 of this Lease,  and (iii) by Seven Million Five Hundred
Thousand Dollars  ($7,500,000),  such offset to be effected by having the annual
Lease payment for the last year of the Lease Term (i.e., the Initial Term if the
Lease Term is not renewed or the  Renewal  Term if the Lease Term is renewed) be
Thirty  Million  Five  Hundred  Thousand  Dollars  ($30,500,000),  with the last
quarterly  payment to be Two  Million  Dollars  ($2,000,000),  rather  than Nine
Million Five Hundred Thousand Dollars ($9,500,000).

         13.12 Guarantee of Lessor's Obligations.  AMSC Parent hereby guarantees
               ---------------------------------
absolutely,  irrevocably  and  unconditionally  to the Lessee the  complete  and
prompt  observance,  fulfillment and performance of each and every provision and
obligation  of the  Lessor  under this Lease or under the  Service  Contract  or
License Agreement,  and hereby covenants and agrees that it shall pay the amount
of any damages or other loss suffered by the Lessee as a result of the breach of
any  covenant  or  provision  of this  Lease,  the  Service  Contract or License
Agreement by the Lessor or as a result of any  misrepresentation  of any fact in
any  representation  and warranty in this Lease, the Service Contract or License
Agreement or in any certified  statement  provided  pursuant to this Lease,  the
Service Contract or License Agreement, without the necessity of the Lessee first
presenting  a claim to, or  bringing  an action or suit  against,  the Lessor or
otherwise  bringing  any action or suit for recovery of such  damages;  provided
that AMSC Parent shall be liable  hereunder  only to the extent of the liability
of the Lessor under this Lease,  the Service  Contract or License  Agreement and
shall be entitled to assert all defenses that could be asserted by the Lessor.

<PAGE>

The  guarantees  set forth in this  Section  13.12 shall become  effective  upon
execution  of this Lease by AMSC  Parent and shall  remain in effect in favor of
the Lessee until the later of the  performance in full of all of the obligations
of the Lessor hereunder and under the Service Contract and License  Agreement or
the release in writing by the Lessee.  The obligations of AMSC Parent under this
Section  shall be absolute and  unconditional,  irrespective  of any  amendment,
modification  or change  of any other  Section  of this  Lease or any  waiver of
compliance  with any  obligation  hereunder.  No  assignment or transfer by AMSC
Parent and no termination,  amendment,  waiver or modification of this guarantee
or any of its terms or provisions  shall be effective  against the Lessee unless
it is set forth in a written instrument signed by AMSC Parent and the Lessee.

         13.13 Technical Operations  Committee.  The Lessor and the Lessee shall
               -------------------------------
establish  a  technical   operations   committee  (the   "Technical   Operations
Committee")  consisting  of one  representative  from each of the Lessor and the
Lessee (and an alternate member from each). The Lessor and the Lessee may submit
to the Technical  Operations Committee for clarification or confirmation matters
related  to the  operation  of the  provisions  of this  Lease  concerning  safe
operation or the health and safety of the  Satellite.  The Technical  Operations
Committee  shall also be the first step in the dispute  resolution  process with
respect to matters  involving  the health or safety of the Satellite as provided
in Section  13.6.  If the members of the Technical  Operations  Committee  shall
agree on a particular  interpretation  of a provision  of this Lease  related to
matters  within  the  Committee's   mandate,   then  actions  pursuant  to  such
agreed-upon  interpretation  shall  presumptively  be deemed to be in compliance
with this Lease.

         13.14 Lease  Characterization.  The parties agree that the lease of the
               -----------------------
Satellite by the Lessor to the Lessee shall be characterized for purposes of all
applicable law as an operating lease.  Notwithstanding any provisions  expressed
in or implied by this Lease,  property in and title to the Satellite shall at no
time pass to the Lessee and the Satellite shall at all times remain the property
of the Lessor.  The Lessee  shall take all actions and execute all  documents as
may  reasonably  be requested by the Lessor to implement  the  intention of this
Section 13.14.

                                ~~ end of page ~~
                        [signatures appear on next page]


<PAGE>






     IN WITNESS  WHEREOF,  the parties hereto have executed this Lease as of the
day and year first above written.

                         AMSC SUBSIDIARY CORPORATION



                         By   /s/GARY M. PARSONS
                         Name:   Gary M. Parsons
                         Title:  Chief Executive Officer and President



                         AMERICAN MOBILE SATELLITE CORPORATION
                         (as Guarantor)



                         By   /s/GARY M. PARSONS
                         Name:   Gary M. Parsons
                         Title:  Chief Executive Officer and President



                         AFRICAN CONTINENTAL TELECOMMUNICATIONS LTD.



                         By   /s/C.P. DOLLERY
                         Name:   C.P. Dollery
                         Title:  Vice Chairman






<PAGE>




                                    Exhibit A
                              CERTAIN DEFINED TERMS

     13.1    $ shall mean United States dollars.

     13.2    African  Performance  Tests are tests and analyses conducted at the
             ---------------------------
Relocated  Orbital  Position to verify that the Satellite  operates as specified
and can  perform  acceptably.  The  African  Performance  Tests are set forth on
Schedule 2.1.
- ------------

     13.3    Applicable  Legal Requirements means satisfying requirements of all
             ------------------------------
laws,  statutes,  ordinances,  rules  and  regulations  affecting  or in any way
relating to the relevant subject matter, including, without limitation, those of
governmental entities and international organizations (including the ITU) having
jurisdiction and including,  without  limitation,  obtaining and maintaining any
applicable licenses and approvals.

     13.4    Assign means to grant, transfer,  sell, assign, charge,  mortgage,
             ------
encumber or otherwise convey directly or indirectly, in whole or in part.

     13.5    Bankruptcy Event with respect  to a person means (i) the voluntary
             ----------------
commencement  of any  proceeding,  or  voluntary  filing,  by such  person  of a
petition seeking liquidation,  reorganization,  arrangement or readjustment,  in
any  form,  of  such  person's  debts  under  any   jurisdiction's   insolvency,
liquidation or similar laws (each such  jurisdiction's laws being referred to as
a  Bankruptcy  Law),  or such  person's  filing  of an answer  consenting  to or
acquiescing  in any such  petition,  or (ii) the  making  by such  person of any
general  assignment for the benefit of such person's  creditors or the admission
by such person in writing of such person's  inability to pay such person's debts
as they  mature,  or (iii) the  consent  by such  person to the  filing  of, the
failure  by such  person to  contravene  successfully  with  respect  to, or the
granting of an order of relief with respect to (A) any  involuntary  petition or
application  under any Bankruptcy Law seeking an application for the appointment
of a receiver,  trustee,  custodian,  sequestrator  or similar  official for the
assets of such person, or (B) any involuntary  petition or application under any
Bankruptcy Law seeking liquidation, reorganization,  arrangement or readjustment
of such person's  debts under any Bankruptcy  Law, or (iv) the  appointment of a
receiver, trustee, custodian, sequestrator or similar official for the assets of
such person under any Bankruptcy Law or otherwise.

     13.6    CMIS Expenses are those expenses to be paid by the Lessor under the
             -------------
License Agreement and Service Contract.

     13.7    CMIS Sublicense Agreement means that "Sublicense Agreement for TMI
             -------------------------
Technology" of even date herewith  between the Lessor and the Lessee relating to
the sublicense of certain intellectual property of TMI, or intellectual property
on license to TMI, relating to a certain customer management information system.

<PAGE>

     13.8    Commercial  Service  Date means the date when the  Lessee  begins
             -------------------------
providing or is technically  capable of providing  commercial  service using the
Satellite and its ground-based communication facilities.

     13.9     Constructive Total Loss means a Constructive Total Loss as defined
              -----------------------
in the in-orbit  policy referred to in Section 2.2 or if no such policy shall be
in place, then a Constructive Total Loss as defined in AMSC's in-orbit insurance
policy for the Satellite as of the date of this Lease.

     13.10   End of Life or EOL shall mean the earlier of March 31, 2005;  the
             -----------    ---
date on which, in Lessor's reasonable judgment,  less than 42 Kg of fuel remains
(including any uncertainty in the estimate of fuel); and the first date on which
the  Satellite  is unable to  transmit  or receive on Beams 1, 2 or 3  (Central,
Mountain or West) despite the use of all available backup capacity.

     13.11   FCC means the Federal Communications Commission.
             ---

     13.12   Ground  Segment   Contracts   shall  mean  the  CMIS  Sublicense
             ---------------------------
Agreement,  the License Agreement, the Service Contract and any other agreements
entered into in connection with the foregoing.

     13.13   Guarantor  means  the  guarantor  of  the  Lessee's  obligations
             ---------
pursuant to Section 9 of the Lease.  The Lessor may designate  another parent or
subsidiary of the Lessee or of the  Guarantor as an additional  Guarantor if, in
the opinion of the Lessor,  the additional  financial  assurances of that person
would reasonably be required.

     13.14   Initial AMSC Payment  Expenses means an amount up to Five Million
             ------------------------------
Dollars  ($5,000,000)  which is expended by AMSC on the Lease and expenses under
the Ground Segment Contracts. The Initial AMSC Payment Expenses shall be paid by
the Lessee to AMSC on the Start Date.

     13.15   Initial  Payment  means  the Ten  Million  Dollar  ($10,000,000)
             ----------------
payment to AMSC,  Seven Million Five Hundred  Thousand  Dollars  ($7,500,000) of
which  shall be paid  upon the  Satellite  Contract  Date and Two  Million  Five
Hundred  Thousand  Dollars  ($2,500,000)  of which shall be paid,  and which the
Lessee  agrees to pay,  no later  than the date  forty-five  (45) days after the
Satellite Contract Date. Up to Five Million Dollars  ($5,000,000) of the Initial
Payment is to be used to fund those  expenses to be incurred under the Lease and
Ground  Segment  Contracts  as  directed  by  the  Lessee,  including  satellite
inversion  software,  other project  development and management  expenses,  TT&C
Services, or otherwise.

     13.16   ITU means the International Telecommunication Union.
             ---

     13.17   Lessee's  Agents  includes  all  agents,  directors,  employees,
             ----------------
officers, partners, owners, contractors, licensees or invitees of the Lessee.

     13.18   License  Agreement  means  that  intellectual  property  License
             ------------------
Agreement of even date  herewith  between the Lessor and the Lessee  relating to
the license of certain  intellectual  property of the Lessor and the Lessee,  or
intellectual  property  on  license  to the  Lessor,  relating  to  ground-based
communication facilities.

<PAGE>

     13.19   Minimum  Performance  Specifications  shall have the meaning set
             ------------------------------------
forth in the Test Plan.

     13.20   North American Performance Tests are tests and analyses conducted
             --------------------------------
to verify that the Satellite  operates as specified  and can perform  acceptably
when moved to the Relocated  Orbital  Position.  The North American  Performance
Tests are set forth on Schedule 2.1.  Performance  Tests shall be carried out at
                       ------------
mutually  agreed  locations in North America  corresponding  to the locations of
Johannesburg  and selected  other points in Africa once the  Satellite is moved.
The test results  shall  provide the  performance  baseline to use in evaluating
satellite performance after relocation.

     13.21   Offering  means the public  floatation of equity of the Lessee or
             --------
its  permitted  assignee  on the  Johannesburg  stock  exchange  or any  similar
offering or  offerings  of equity with gross  proceeds to the issuer of at least
One Hundred Twenty Million Dollars ($120,000,000).

     13.22   On Station  Acceptance  means the Satellite has been moved to the
             ----------------------
Relocated Orbital Position and the African Performance Tests have been completed
with results meeting the Minimum Performance Specifications at such location.

     13.23   On  Station  Acceptance  Date  means the date on which On Station
             -----------------------------
Acceptance occurs.

     13.24   Partial Loss means a loss in Satellite  performance that is not a
             ------------
Total Loss or a Constructive Total Loss.

     13.25   Post-Offering  Payment means a payment of  Twenty-Eight  Million
             ----------------------
Dollars  ($28,000,000)  by the  Lessee to the  Lessor  minus  any Space  Segment
Expenses with respect to which the Lessee had previously reimbursed the Lessor.

     13.26   Relocated  Orbital  Position  means  the  geostationary  orbital
             ----------------------------
position  located at  11.5(degree)  East  Longitude or such other nearby orbital
position as may be required for satellite frequency coordination.

     13.27   Relocation  Commencement  Date means the date on which the Lessor
             ------------------------------
begins relocation of the Satellite to the Relocated Orbital Position.

     13.28   Returned Orbital Position means the geostationary  orbit position
             -------------------------
located at  101(degree)  West  Longitude or such other  orbital  position as the
Lessor  shall  designate  which will not be a  U.K.-sponsored  orbital  position
unless separately negotiated.

     13.29   Satellite means the MSAT-2 (M-2) satellite also known as AMSC-1,
             ---------
acquired  pursuant to the American Mobile  Satellite  Corporation  Contract with
Hughes Aircraft Company for an MSAT Spacecraft, Contract No. AMSC-S/C-11/90/001,
dated November 29, 1990.

     13.30  Satellite Contract Date means the date of the signing of this Lease.
            -----------------------

<PAGE>

     13.31   Satellite  Relocation Date means such date, on or after the Start
             --------------------------
Date, when the following  conditions have been satisfied or waived in writing by
the Lessor:

             (i)   Performance  Tests  are  complete  and  the  Lessee  has  not
                   terminated this Lease under Section 5.1(a)(ii);

             (ii)  receipt of all necessary government approvals (including 
                   American,  Canadian, English, South African, or  otherwise)  
                   to move the  Satellite to the Relocated Orbital Position;

             (iii) the Lessee has obtained final approval under all  Applicable
                   Legal Requirements for the Satellite to occupy the Relocated 
                   Orbital Position, including coordination of frequencies for  
                   TT&C  and  initial operation;

             (iv)  the  Lessor  has  approved,  in  its  reasonable  discretion,
                   the contracts for the construction of the TT&C facilities;

             (v)   the  Lessor  shall  have  determined,  in  its  reasonable
                   discretion,   that  the  TT&C   facilities   have  been
                   completed  sufficiently to safely permit  relocation of
                   the Satellite to begin;

             (vi)  the  Lessor  shall  have  determined,  in  its  reasonable
                   discretion,  that the ground  segment  facilities  have
                   been or will be completed sufficiently to safely permit
                   testing  of  the  Satellite  at the  Relocated  Orbital
                   Position;

             (vii) the Offering has occurred;

             (viii) the Lessee has paid the Post-Offering Payment to the Lessor;
                   and

             (ix)  there is no Event of Default.

         13.32 Service Contract means the services  agreement between the Lessee
               ----------------
and the Lessor of even date herewith.

         13.33 Space Segment Expenses means the expenses the Lessor incurred for
               ----------------------
Satellite inversion, TT&C drift expenses, insurance for the Lessee's benefit and
Satellite testing expenses.

         13.34 Start  Date  means  the  date  on  which  the  Lessee  makes  the
               -----------
Post-Offering Payment, which shall not be more than ten (10) days after the date
of the Offering.

<PAGE>

         13.35 Test Plan means the test plan set forth on  Schedule  2.1,  which
               ---------                                   -------------
sets forth the North  American  Performance  Tests and the  African  Performance
Tests.

         13.36 TMI Satellite means the MSAT-1 (M-1) satellite owned by TMI.
               -------------

         13.37 Total  Loss  means  a  Total  Loss as  defined  in the  in-orbit
               -----------
insurance  policy  referred to in Section  2.2 or if no such policy  shall be in
place,  then Total Loss as defined in AMSC's in-orbit  insurance  policy for the
Satellite in place as of the date of this Lease.

         13.38 TT&C means telemetry, tracking and control.
               ----

         13.39 TT&C Services  means  telemetry,  tracking and control  services,
               -------------
drift orbit  operations and other  operational  services in connection  with the
Satellite.

<PAGE>

                                    Exhibit B

                                     FORM OF
                      Certificate of Lessee [and Guarantor]



              This  Certificate  is given  pursuant  to Section  6(a)(vi) of the
Satellite Lease Agreement for the AMSC-1 Satellite.

              In reliance on the  Certificates  of AMSC  Subsidiary  Corporation
("AMSC") and American Mobile Satellite Corporation ("AMSC Parent"),  dated as of
the same date as this  Certificate,  copies of which are  attached  hereto,  the
undersigned  Lessee [and Guarantor]  under such Satellite Lease Agreement hereby
certify to AMSC and AMSC Parent as follows:

                      1. The Satellite  Lease  Agreement is and remains a valid,
              binding agreement among the parties thereto.

                      2. The Satellite  Lease  Agreement has not been terminated
              and remains in full force and effect.

                      3. The Lessee [and the Guarantor]  have made to the Lessor
              all payments  due to the Lessor as of the date hereof  pursuant to
              the Satellite Lease Agreement.

                      4. As of this date, the Lessee has no ability to terminate
              the Satellite Lease Agreement pursuant to the terms thereof.


                                ~~ end of page ~~
                      [signatures appear on following page]



<PAGE>




              IN WITNESS WHEREOF, the undersigned have executed this Certificate
as of the        day of                 , 199 .
          ------        ----------------     -


[LESSEE]


By
Name:
Title:




[[GUARANTOR]



By
Name:
Title:]

                



<PAGE>




                                     FORM OF
                      Certificate of Lessor and AMSC Parent



              In reliance on the Certificate of                       ("Lessee")
                                                ---------------------
[and                         ("Guarantor")],  dated as of the same  date as this
      ---------------------
Certificate,  a  copy  of  which  are  attached  hereto,  the  undersigned  AMSC
Subsidiary  Corporation and American  Mobile  Satellite  Corporation  under such
Satellite Lease Agreement hereby certify to Lessee [and Guarantor] as follows:

                      1. The Satellite  Lease  Agreement is and remains a valid,
binding agreement among the parties thereto.

                      2. The Satellite  Lease  Agreement has not been terminated
and remains in full force and effect.

                      3.  The Lessee [and the Guarantor] have made to the Lessor
all  payments due to the Lessor as of the date hereof pursuant to the Satellite 
Lease Agreement.

                      4. As of this date, the Lessee has no ability to terminate
the Satellite Lease Agreement pursuant to the terms thereof.


                                ~~ end of page ~~
                      [signatures appear on following page]

 

<PAGE>




              IN WITNESS WHEREOF, the undersigned have executed this Certificate
as of the        day of                , 199 .
          ------        ---------------     -


AMSC SUBSIDIARY CORPORATION



By
Name:
Title:



AMERICAN MOBILE SATELLITE CORPORATION



By
Name:
Title:







<PAGE>




                                    Exhibit C





                                FORM OF GUARANTEE








         Reference is made to the SATELLITE  LEASE  AGREEMENT (the "Lease") made
     as of  the  2nd  day  of  December,  1997,  by and  among  AMSC  Subsidiary
     Corporation, a Delaware corporation, American Mobile Satellite Corporation,
     a Delaware corporation, and African Continental  Telecommunications Ltd., a
     Gibraltar  company.  Capitalized  terms not otherwise  defined herein shall
     have the meanings set forth in the Lease.


          The  Guarantor   hereby   guarantees   absolutely,   irrevocably   and
     unconditionally   to  the  Lessor  the  complete  and  prompt   observance,
     fulfillment  and  performance of each and every provision and obligation of
     the  Lessee  under the  Lease or under  the  Service  Contract  or  License
     Agreement,  and hereby covenants and agrees that it shall pay the amount of
     any damages or other loss  suffered by the Lessor as a result of the breach
     of any covenant or provision of the Lease,  the Service Contract or License
     Agreement by the Lessee or as a result of any misrepresentation of any fact
     in any  representation  and warranty in the Lease,  the Service Contract or
     License  Agreement or in any certified  statement  provided pursuant to the
     Lease, the Service Contract or License Agreement,  without the necessity of
     the  Lessor  first  presenting  a claim to, or  bringing  an action or suit
     against,  the Lessee or otherwise  bringing any action or suit for recovery
     of such damages; provided that the Guarantor shall be liable hereunder only
     to the extent of the  liability of the Lessee under the Lease,  the Service
     Contract or License  Agreement and shall be entitled to assert all defenses
     that could be asserted by the Lessee.


          The guarantees set forth in this Guarantee shall become effective upon
     execution by the Guarantor of this  Guarantee and shall remain in effect in
     favor of the Lessor  until the later of the  performance  in full of all of
     the  obligations  of the  Lessee  under the  Lease  and  under the  Service
     Contract and License Agreement or the release in writing by the Lessor. The
     obligations  of the Guarantor  under this  Guarantee  shall be absolute and
     unconditional, irrespective of any amendment, modification or change of any
     other Section of the Lease, the Service  Contract or the License  Agreement
     or any waiver of compliance with any obligation hereunder. No assignment or
     transfer  by  the  Guarantor  and  no  termination,  amendment,  waiver  or
     modification  of this guarantee or any of its terms or provisions  shall be
     effective against the Lessor unless it is set forth in a written instrument
     signed by the Guarantor and the Lessor.


         Representations and Warranties.   The  Guarantor  hereby represents and
     warrants to the Lessor:


         13.39.1(a)  that the Guarantor is a corporation duly organized, validly
     existing and in good standing under the laws of                 , with full
                                                     ---------------- 
     corporate power, right and authority to  execute  and to deliver this Lease
     and  to  enter into  and  to perform the obligations  of  the  Guarantor
     hereunder;


         13.39.1(b) that the execution and delivery of this Lease by the officer
     so  doing,  and  the  performance  of  the  obligations  of  the  Guarantor
     hereunder,  have  been duly authorized by all necessary corporate action on
     the part of the Guarantor;


         13.39.1(c)  that  this  Lease  is a valid and binding obligation of the
     Guarantor, enforceable against the Guarantor in accordance with its terms;


          that the execution,  delivery and performance of the Guarantee and the
     performance  of  the  obligations  of the  Guarantor  hereunder  shall  not
     constitute a breach,  violation  or default of (i) any  material  contract,
     indenture,  deed of trust,  loan, note,  lease,  service agreement or other
     instrument  to which the  Guarantee  is subject or is a party;  or (ii) any
     law, rule, regulation,  ordinance,  judgment,  decree, order,  governmental
     permit or license to which the Guarantor is subject.


                                ~~ end of page ~~


                      [signatures appear on following page]

<PAGE>




              IN WITNESS WHEREOF, the undersigned has executed this Guarantee as
of the        day of                 , 199 .
       ------        ----------------     -




 [[GUARANTOR]











By


Name:


Title:]





<PAGE>




                                    EXHIBIT D



                             CHOICE OF LAW AGREEMENT







              This  CHOICE OF LAW  AGREEMENT  (this  "Agreement")  is made as of
     December 2, 1997, by and among AMSC Subsidiary  Corporation,  a corporation
     incorporated  under  the laws of the  State of  Delaware,  American  Mobile
     Satellite  Corporation,  a Delaware  corporation,  and African  Continental
     Telecommunications Ltd., a Gibraltar company.





                                   WITNESSETH:



              WHEREAS,  the parties  entered  into a Satellite  Lease  Agreement
dated as of December 2, 1997 (the "Satellite Lease Agreement");

              WHEREAS,  pursuant to the Satellite Lease  Agreement,  the parties
thereto have agreed that the Satellite  Lease  Agreement shall be construed and 
enforced  in  accordance  with  the  laws of the State of Delaware and that  all
proceedings  with respect to the Satellite  Lease  Agreement  shall be  brought 
only in Delaware; and

              WHEREAS, the parties wish to confirm that their choice of Delaware
law shall be enforceable in accordance with 6 Del. C. Section 2708.
                                              ---  --

              NOW,  THEREFORE,  in consideration of the foregoing and other good
and  valuable  consideration,  the receipt and  sufficiency  of which are hereby
acknowledged, the parties agree as follows:


              1.      Single Undertaking. This Agreement and the Satellite Lease
                      ------------------
Agreement and  the  other documents referred  to or provided for therein and the
transactions  contemplated  thereby  shall  be  read  and  construed as a single
undertaking among the parties.

              2. Consent to Jurisdiction. The parties irrevocably consent to the
                 -----------------------
exclusive jurisdiction of arbitration in the State of Delaware for all purposes 
in connection with any action or proceeding that arises out of or relates to the
Satellite  Lease  Agreement (collectively,  "Proceedings").  The  parties hereby
agree that service of summons,  complaint,  or other process in connection  with
any  Proceedings  may be  made  as set  forth in the Satellite  Lease  Agreement
with  respect  to  service  of  notices,  and  that service so made shall be as 
effective as if personally made in the State of Delaware.

              3. Acknowledgments.  As set forth in the Satellite Lease Agreement
                 ---------------
and in Section 2 above, it is the intent of each of the parties hereto that all 
Proceedings be heard exclusively  through  arbitration in the State of Delaware.
Each of the parties hereto  acknowledges  that (i) it has freely agreed that all
Proceedings  will  be  heard  in  accordance  with  Section  2  above, (ii) the 
agreement to choose arbitration in the State of Delaware to hear all Proceedings
in accordance  with Section 2 above is reasonable and will  not place such party
at  a  disadvantage  or  otherwise  deny  it  its  day  in  court, (iii) it is a
knowledgeable, informed, sophisticated business entity capable of  understanding
and  evaluating the provisions set forth in this Agreement, including Section 2,
and  (iv)  it  has  been  represented  by such counsel and other advisors of its
choosing  as  it  has deemed appropriate in  connection  with  its  decision  to
enter  into  this  Agreement,  including Section 2.

              4.  Appointment  of Agent.  For purpose of further  effecting  the
                  ---------------------
parties'  agreements  set  forth in the Satellite Lease Agreement and Section  2
above, (i) the parties hereby irrevocably  appoint Corporation  Service Company,
1013 Centre Road,  Wilmington,  Delaware  19805, as its agent for  acceptance of
legal process in the State of Delaware in connection  with  any Proceeding,  and
each party  agrees that  service upon its agent shall have  the same legal force
and effect as if served upon it personally  within the State of Delaware.

              5.   Governing Law.   This  Agreement  shall  be  governed by, and
                   -------------
construed  and  enforced  in  accordance with, the internal laws of the State of
Delaware.





                                ~~ end of page ~~

                        [signatures appear on next page]




<PAGE>



             IN WITNESS WHEREOF, the parties hereto have executed this Agreement
as of the day and year first above written.





AMSC SUBSIDIARY CORPORATION











By


Name:


Title:











AMERICAN MOBILE SATELLITE CORPORATION











By


Name:


Title:











AFRICAN CONTINENTAL TELECOMMUNICATIONS LTD.











By


Name:


Title:




<PAGE>

                                  Schedule 1.3
                           WIRE TRANSFER INSTRUCTIONS
                                    OF LESSOR




<TABLE>
<CAPTION>



<S>                               <C>    
Bank Name:                        Wachovia Bank of North Carolina

Address:                          100 N. Main Street
                                  Winston-Salem, NC

ABA No.:                          053 100 494

Account Name:                     AMSC Subsidiary Corporation

Account Number:                   8738-071423

Reference:                        Include invoice number, if applicable

AMSC Contact:                     Geri Hopkins
                                  Manager, Treasury Operations
                                    703-758-6453


</TABLE>


Schedule 1.3                                                              Page 1


<PAGE>


                                  SCHEDULE 2.1

                    SATELLITE RELOCATION AND ACCEPTANCE PLAN

SUMMARY

The following are the major steps in the relocation of the Satellite.

Remove traffic from the Satellite.  If practicable,  Telesat will assume control
     from Panamsat at this time.

Adjust ESA and RPMs to the  configuration  to be used at the  Relocated  Orbital
Position.

Conduct the  North  American Performance Test (a.) t o verify that the Satellite
     Operates  as  described  and  can  perform  acceptably  when  moved  to the
     Relocated  Orbital  Location, and (b.) to  obtain  a  set of baseline data.
     These test are summarized below.

If   required,  reorient the Satellite to its nominal  configuration and restore
     traffic  to  the  Satellite  until  the  Satellite  Relocation  Date,  then
     permanently remove traffic from the Satellite.

Drift the Satellite from 101 degrees West to the Relocated  Orbital  Position.  
     Transfer orbit facilities in Chilworth England will be  upgraded to receive
     the Satellite and initially  operate it until TT&C  facilities at Gibraltar
     and Johannesburg are completed.

Invert and reorient the Satellite and re-adjust RPMs and ESA if required.

Conduct the African  Performance  Test, which are a subset of the North American
     Performance  Tests to be repeated at  Johannesburg  and a few other African
     points once the  Satellite has reached the  Relocated  Orbital  Position to
     validate that  coverage is correct and  relocation of the Satellite has not
     degraded performance.


Schedule 2.1                                                              Page 1



<PAGE>





AMSC-1 TEST PLAN DESCRIPTION

The following  summarizes  the test planned for both the North  American and the
African Performance Test.

Test Plan Objective

The  proposed  plan is to test the  satellite  in North  America  at or near its
current  location at 101oW.  to both verify  performance  and to obtain a set of
baseline  data.  These tests would then be repeated in Africa once the satellite
has  reached  the  Relocated  Orbital  Position  and is pointed  correctly.  The
accompanying  diagrams assume this position is 18o East;  slight  adjustments to
the test points may be needed to accommodate a different orbital location.

The purpose of the test would be as follows:

To verify the L-Band satellite EIRP performance for each of the four beams.

Using the measured  EIRP data to verify that the satellite  antenna  pointing is
correct.

To verify the L-Band satellite receive performance for each of the four beams.

To verify the Ku-Band satellite receive performance (one location only).

To verify the Ku-Band downlink performance (one location only).

The main  element of the testing will be to verify that the  satellite  expected
coverage is available both in North America and at the new orbital location over
Africa.

Payload Test

The  following  payload test will be performed  as  appropriate  on the forward,
reverse and Ku-Ku links.

AEIRP and NFD will be measured for all transmit beams,

NPR  will be measured  at the  original  orbital  loation of 101.0o W for health
     verification purposes only,

G/T will be measured for all receive beams; spare receivers will be verified in 
     pre-designated beams,

All sub-bands will be functionally verified, and

All step attenuators will be functionally verified.

Schedule 2.1                                                              Page 2

<PAGE>



Mobile Test System

It is  proposed  to use the AMSC  mobile  L-band  EIRP test  system  to  confirm
satellite L-Band EIRP and L-Band Receive G/T at three test locations.

In addition,  a TMI designed and  assembled  mobile uplink test system with both
Ku-band and L-band  transmit and receive  capability will be deployed during the
test phase.  The system would  include a Ku-Band HPA  transmitting  via a ground
based high gain Ku-Band antenna sufficient to exercise the satellites Ku-Band to
L-Band Transponder.
Figure 1 shows the configuration of this test system as now proposed.

Test Point Locations

Test  points  will be  selected  to enable  all four  beams to be tested  from a
minimum number of test locations (three are proposed). Test Point 3 will be used
for both  Beam 1 and  Beam 4  testing.  It is  proposed  that the test  point be
selected to correspond to the following geographic locations in Africa:

      Test Point 1 at Pretoria or alternately Johannesburg (Ku + L-Band transmit
 and receive)

      Test Point 2 at Windhoek, Namibia (L-Band transmit and receive only)

      Test Point 3 at Cabinda,  Congo (L-Band transmit and receive only) (Beam
1 and Beam 4)

Final  selection of test locations will be determined  following final selection
of satellite orbital slot and associated satellite pointing.

Note that it is proposed to leave the Ku-Band  link test set at one  location to
simplify  logistics and to ensure a satisfactory and stable uplink signal level.
Uplinking  from Pretoria or  Johannesburg  has the  advantage  that the Ku- band
signal will be received near the antenna boresight, hence minimizing uplink EIRP
requirements.

At each test location the  measurement  of two beams will be possible,  and this
will  assist  in  verifying  both  satellite  repeater  performance  as  well as
satellite  antenna  pointing.  Data will be  collected  over a 24 hour period to
account  for any  thermal  variations.  All  measurements  will  be  made  using
calibrated equipment and within the small signal region of the satellite payload
transponders.

Figure 2 shows the proposed test locations in Africa and the corresponding  beam
coverage at L-Band.

Figure 3 shows the  approximate  location of the three test points on the L-band
pattern when the satellite is located at 101oo W. with assumed nominal  coverage
of the USA.

Figure 4 shows the coverage  when the satellite  nominal  pointing is changed by
approximately  1.9o to the  South  to  enable  measurements  to be  conveniently
carried out at three locations in North and Central America. Note that this bias
is exactly the amount assumed for ESA shift to optimize coverage of Africa.

Please note that coverage shown for all for the above figures is approximate and
only for illustrative purposes.

Fuel Lifetime Estimate

Lessee and Lessor will mutually agree on a method to estimate the remaining fuel
life of the Satellite at the Relocated Orbital Position.


Schedule 2.1                                                              Page 3



<PAGE>



                                  Schedule 2.3
                            LESSEE'S TT&C FACILITIES
                                  AND SERVICES



Requirements of TT&C Facilities to be provided by Lessee
- --------------------------------------------------------

Introduction
- ------------

Lessee  shall  provide  Tracking  Telemetry  and Command  (TTAC)  equipment  and
facilities  as  outlined  herein  suitable  to  allow  transfer  to and  ongoing
operations at the  Relocated  Orbital  Position.  Lessee agrees to provide three
control  facilities  each  capable of  controlling  the  Satellite  via its omni
antenna.  One  facility  will be located  within the beam of the  communications
antenna  pattern in a location  such as  Johannesburg,  South Africa and will be
capable of controlling  the Satellite  using its directive  antenna as well. The
second  primary  site is to be  located  in  Gibraltar.  The third site shall be
located in Chilworth, England and shall be used for transfer orbit maneuvers via
the  Satellite's  omni antenna.  The  Chilworth  site will also be available for
performing   the   post-drift   testing   and  systems   integration   with  the
communications  ground  segment.  The Lessee  will  inform the Lessor  three (3)
months prior to the  Chilworth  station  being ready to receive the Satellite to
allow traffic transfer and Pre-Drift IOT to be performed.  The Johannesburg site
will be available prior to commencing revenue service.  All sites will be linked
to a satellite  control  facility  using  redundant  International  Private Line
64kbps circuits.


Facilities requirements
- -----------------------

At  each  site,  facilities  suitable  for  a  Satellite  Control System will be
provided  including but not limited to the  following;
               Diesel  backed UPS power with a rated power  capacity of not less
               than 50 kVA  Environmentally  controlled  building,  with  raised
               computer  floor  for  the   installation  of  satellite   control
               equipment.  Suitable land area for two antennas,  one 8 meters in
               diameter,  and one 4.5 meters in  diameter.  Lessee will  provide
               suitable antenna  foundations as per each antenna  manufacturer's
               recommendations. The antenna foundations will be not more than 25
               meters from where the high power  amplifiers are  installed.  All
               environmental control of facilities shall meet recommendations as
               outlined by the  provider  of the  Satellite  Control  Equipment.
               Access to the site shall be possible for heavy  equipment such as
               cranes.


Schedule 2.3                                                              Page 1


<PAGE>


Lessee will  provide suitable  communications  facilities  to  allow  control of
the satellite  from a remote  location.  Facilities required  are;  
               Standard  DTMF  tone dial  telephone  services
               Facsimile  services ISDN services  accessible  internationally
               The site shall be  serviceable by  International  Private Line
               services at data rates of 64 kbps minimum.

Lessee shall  provide  communications  equipment  suitable for  controlling  the
satellite  from a remote  site as per the  requirements  of the  provider of the
Satellite Control System.

Antennas and RF  requirements
- -----------------------------

Lessee shall  provide two antennas at each site.  The prime antenna shall have a
minimum  diameter  of 8 meters and the back up antenna a diameter of 4.5 meters.
The high power amplifiers (HPAs) shall be 2.5 kilowatt  klystrons  yielding with
the antenna an minimum EIRP of 88 dBW. An EIRP of 88 dBW will provide  effective
commanding  through the spacecraft omni antenna,  providing an expected  command
margin of 15 dB clear sky,  assuming a worst case command threshold flux density
of -90 dBW/m2 via the omni.

The 8 meter antenna will have the following characteristics;
         Full monopulse tracker using TE21 tracking coupler with Antenna Control
         Unit  Four port  linearly  polarized  feed +/- 90  degree  polarization
         adjustment  Minimum 120 degree sector azimuth  coverage Feed capable of
         handling 3kW RF power minimum. G/T of 34 dB/K minimum.
The 34 dB/K antenna  performance will provide a minimum telemetry margin of 11.3
dB, with respect to a 1E-6 Bit Error Rate,  assuming a 4 kilobit data rate and a
spacecraft EIRP of 7dBW nominal through the omni.

The RF system will be equipped with redundant up and down converters,  redundant
LNA's and HPA's.

The high power  waveguide  combining  system  will allow  routing of the command
signal to either the backup (4.5 meter) or the primary (8 meter) antenna using a
variable power combining system.

The 4.5 meter antenna will allow command and telemetry operations during periods
when  the 8 meter  antenna  is not  available  due to  repair,  maintenance  and
overhaul.  The EIRP is to be 83 dBW  minimum  and the G/T is 29 dB/K.  This will
provide an expected  margin of 6 dB for  telemetry  via the  satellite'  s omni,
suitable  to back up the 8 meter  under  clear sky  conditions.  Margins via the
Satellite's communication antenna will be 10 dB's higher nominally.

Schedule 2.3                                                              Page 2

<PAGE>

Computers and Baseband equipment
- --------------------------------

Lessee shall provide  computers  with  associated  software to allow full remote
command,  telemetry  and range  functions  to be performed at the station from a
remote Satellite  Control facility.  The monitor and control equipment  provided
shall  allow  remote  control  and  monitoring  of  all  the  satellite  control
facility's subsystems.  The systems provided shall be fully redundant at each of
the TTAC  stations.  The  software  shall be suitably  modified  and upgraded to
permit full processing of command and telemetry data for the Lessee  spacecraft.
Local display  consoles shall be installed  which will display local  spacecraft
telemetry data to support  emergency  spacecraft  operations should control from
the remote Satellite Control Facility not be available. The system will allow an
operator  to send  manual  commands  to the  spacecraft  using the  front  panel
controls  of  the  command  generator.  Baseband  equipment  includes  telemetry
receivers, FM modulators, command generators,  telemetry processors,  computers,
display  systems,  range  tone  generator  processors,  bit  synchronizers,  PSK
demodulators and associated patch panels.



Schedule 2.3                                                              Page 3



<PAGE>



                                  Schedule 3.8
                               REPORTING SCHEDULE



The following shall be the reporting schedule for the Lessee to the Lessor:

          Anomaly  Notification shall take place immediately upon the occurrence
          ---------------------
          of any anomaly  that  threatens or affects the health or safety of the
          Satellite or the  availability of  communications  services via verbal
          and pager  notification  to the Lessor upon  detection  of an anomaly.

          Anomaly Reports shall be generated whenever an anomaly is detected by
          ----------------
          either the TT&C Services provider or by the payload monitoring that is
          being performed  by the  Lessee.  In the  case  of  any  anomaly  that
          threatens or  affects  the  health or safety of the  Satellite  or the
          availability of  communications  services,  this  report  shall  be  a
          detailed description along with supporting technical data and shall be
          provided no more than two (2) days after  anomaly  has  occurred.  All
          other anomaly reports  shall be summarized  and included in the System
          Status Report.

          Anomaly  Investigation  Reports  shall be  generated  no more than one
          -------------------------------
          month from  detection  of any anomaly  that  threatens  or affects the
          health  or   safety  of  the   Satellite   or  the   availability   of
          communications  services.  The Anomaly Investigation Report shall be a
          detailed engineering study addressing the cause of the anomaly, impact
          to the Satellite and correction  actions required,  if any, due to the
          anomaly.

          System Control Log: Lessee shall maintain a log showing date, time and
          ------------------
          person  performing  each entry.  The System Control Log shall show the
          completion  of all  planned  events  and note any  unusual,  unplanned
          events with the Satellite or ground system. A copy of the log shall be
          available  for  inspection  at  all  times  and  shall  be  maintained
          throughout the term of the Lease.

          Payload  Utilization  Reports shall be generated on a quarterly  basis
          -----------------------------
          showing on a monthly basis the busy hour  utilization of each beam and
          the busy hour of each matrix of the Satellite.

          Satellite Health Reports shall be generated on a yearly basis suitable
          ------------------------
          for  submission to any outside entity Lessee deems  appropriate.  This
          report  shall  provide a detailed  status of each  subassembly  of the
          craft.




Schedule 3.8                                                              Page 1


<PAGE>



          Satellite Status Reports shall be generated  quarterly with a focus on
          ------------------------
          changes that may have occurred from the last Satellite Health Report.

          System Status  Reports shall be generated  quarterly  summarizing  the
          ----------------------
          status of the Satellite or ground system, with a focus on changes that
          may have occurred since the last System Status Report.




Schedule 3.8                                                              Page 2


<PAGE>



                                  Schedule 3.12
                              ESCROW OF SECURITIES

<TABLE>
<CAPTION>


<S>                                          <C> 
               Name                                   Title/Position
               ----                                   --------------


         C. Paul Dollery                      Vice Chairman, African Continental
                                                   Telecommunications Ltd.


         James R. Walker                       Chief Executive Officer, African
                                             Continental Telecommunications Ltd.


         Tony Leng                                Managing Director, African
                                             Continental Telecommunications Ltd.


         Ernest G. DeNigris                    President, African Continental
                                                  Telecommunications Ltd.


         Michael Johnson                     Chief Financial Officer, African
                                            Continental Telecommunications Ltd.



</TABLE>


Schedule 3.12                                                             Page 1


<PAGE>



                              Schedule 5.1 and 5.2

                        GOVERNMENT APPROVALS AND CONSENTS
                          TO RELOCATE THE SATELLITE AND
                        CONSUMMATE THE LEASE TRANSACTIONS





                       United States Government Approvals

                        Federal Communications Commission

                           Department of Commerce and
                  any other applicable agencies with respect to
                    export control matters or with respect to
                the Satellite and the licensed software under the
                          CGS and the License Agreement




                          Canadian Government Approvals

                                 Industry Canada
                (including under the Bulk Capacity Lease of TMI)
               with respect to change in spectrum and orbital slot
                              for the TMI Satellite

                 Communications Security Establishment (Canada)
                        with respect to the TMI Satellite





Schedule 5.1/5.2                                                          Page 1


<PAGE>





                                  SCHEDULE 10.1

                                LESSOR'S CONSENTS







1.  Approval of the Federal Communications Commission



2.  Export control approval by the Department of Commerce and other government
    agencies, as applicable






Schedule 10.1                                                             Page 1


<PAGE>





                                  SCHEDULE 10.2

                             AMSC PARENT'S CONSENTS






1.  Approval of the Federal Communications Commission



2.  Export control approval by the Department of Commerce and other government 
    agencies, as applicable






Schedule 10.2                                                             Page 1


<PAGE>





                                Schedule 12.1(d)
                                 LESSEE CONSENTS




                         Teleport License from Gibraltar

                      Approval of Relocated Orbit Position

                         Orbital Space License under the
                   Outer Space Act 1986 (Gibraltar) Order 1996
                           (Gibraltar or UK approval)

                       Spectrum approval and coordination




Schedule 12.1(d)                                                          Page 1


<PAGE>





                                Schedule 12.1(e)














                     FOUNDERS AND THEIR OWNERSHIP INTERESTS










Schedule 12.1(e)                                                      


<PAGE>



<TABLE>

                         Elcor Satellites (PTY) Limited
<CAPTION>

Shareholder                                            Number of Shares*
- ---------------------------------------------------    ------------------- 
<S>                                                        <C>      
Yancey Family LP                                           8,086,307
Prentiss Yancey                                            8,086,307
Charles Andrews                                            4,917,173
Samuel A. Andrews                                            100,000
Homer B. Walls                                               100,000
J.L. Nelson                                                  100,000
Balozi Harvey                                              4,624,973
Andrew Young                                                 453,622
Victor Labat                                                 453,622
Inner City Broadcasting                                      246,534
Gregory Brown                                             31,326,392
China Victory Investment Limited                           1,918,592
James R. Walker                                            5,329,800
James R. Walker K/A J.A. Tobey                             1,184,400
James R. Walker K/A J.B. Walker                            1,184,400
James R. Walker K/A J.R. Walker                            1,184,400
Michael W. Johnson                                         2,664,900
Michael W. Johnson Jr. Trust                                 888,300
Robert Graham Clark                                        1,184,400
Gary Goodchild                                             1,184,400
Ratory, L.P. (a Delaware limited partnership)              1,184,400
Babacar N'Diaye                                            1,184,400
Investment Facility 581 (PTY) Ltd.                         1,776,600
Kaydon Limited                                             8,883,000
PTC Holdings Limited                                       8,883,000
Tintagle Trading Company Limited                           8,883,000
Thomas Wynne Watts                                         3,553,200
Olivier Chedel                                               888,300
PTC Holdings Limited                                      67,119,850
Comorant Commercial Enterprises LTD                        1,776,600
Elaine Dollery                                             1,776,600
Elcor Holdings Limited                                    11,700,000
Skybird Limited                                            4,700,000
Christopher Paul Dollery                                  20,135,954
Kenly Limited                                             16,779,963
Francis Elaine Dollery                                    13,423,970
Pippin Limited                                            16,779,963
Percy Sutton                                               9,075,493
Touch and Tutor Research and Development                   1,184,790
Charles Andrews                                              592,395
                                                            --------
   Total                                                 305,500,000
</TABLE>


- --------------------------------
* Ordinary shares of R0.001 (one tenth of one cent) each



Schedule 12.1(e)                                                          Page 1


<PAGE>



                                                            EXHIBIT 10.63


               TMI COMMUNICATIONS AND COMPANY, LIMITED PARTNERSHIP


                                     - and -


                           AMSC SUBSIDIARY CORPORATION


                                     - and -


                      AMERICAN MOBILE SATELLITE CORPORATION








                          SATELLITE PURCHASE AGREEMENT

                                December 2, 1997


                                                                


<PAGE>



                               TABLE OF CONTENTS
                                                                            Page
                                                                            ----

                                    ARTICLE 1
                                 INTERPRETATION

Section 1.1.  Definitions....................................................  1
Section 1.2.  Gender and Number..............................................  7
Section 1.3.  Headings.......................................................  7
Section 1.4.  Currency.......................................................  7
Section 1.5.  Certain Phrases, etc...........................................  7
Section 1.6.  Incorporation of Schedules.....................................  7
Section 1.7.  Certificates...................................................  7

                                    ARTICLE 2
                    SALE OF 50% INTEREST IN SHARED SATELLITE

Section 2.1.  Sale of 50% Interest in Shared Satellite.......................  7
Section 2.2.  Satellite Purchase Price.......................................  8
Section 2.3.  Satellite Purchase Price and Prepayment........................  9
Section 2.4.  Closing on Traffic Transfer Date...............................  9
Section 2.5.  Conditions to Traffic Transfer Date and Sale by TMI............  9
Section 2.6.  Conditions to Traffic Transfer Date and Purchase by AMSC....... 11

                                    ARTICLE 3
                      TT&C AND SERVICES OPERATING COMMITTEE

Section 3.1.  TT&C Fees...................................................... 12
Section 3.2.  Services Operating Committee................................... 12
Section 3.3.  Quarterly Reporting............................................ 14
Section 3.4.  Performance Anomalies and Incentive Payments................... 14
Section 3.5.  Satellite Health Reports....................................... 14
Section 3.6.  Radio Frequencies.............................................. 14

                                    ARTICLE 4
                         SATELLITE SHARING ARRANGEMENTS

Section 4.1.  Effect of Traffic Transfer Date................................ 14
Section 4.2.  Orbital Slots.................................................. 15
Section 4.3.  Insurance...................................................... 15
Section 4.4.  Excess Capacity; and Termination of Satellite 
              Capacity Agreement............................................. 16
Section 4.5.  Decommissioning of Satellite................................... 17
Section 4.6.  Exclusion of Liability for Telesat............................. 17
Section 4.7.  Temporary Traffic Transfer..................................... 18

                                       (i)


<PAGE>


                                                                            Page


                                    ARTICLE 5
                                CERTAIN COVENANTS

Section 5.1.  Conduct of Business............................................ 19
Section 5.2.  Satellite Capacity Agreement and Joint Operating Agreement..... 19
Section 5.3.  Reasonable Efforts............................................. 19
Section 5.4.  Confidentiality; Press Releases................................ 19
Section 5.5.  Access to Information.......................................... 20
Section 5.6.  FCC Applications............................................... 20
Section 5.7.  Notices of Certain Events...................................... 20
Section 5.8.  Limitation on Liability to Customers, Resellers, etc........... 21

                                    ARTICLE 6
                         REPRESENTATIONS AND WARRANTIES

Section 6.1.  Representations and Warranties of TMI.......................... 21
Section 6.2.  Representations and Warranties of AMSC......................... 23
Section 6.3.  Disclaimer of Warranties....................................... 24
Section 6.4.  Disclosure..................................................... 25

                                    ARTICLE 7
                              TERM AND TERMINATION

Section 7.1.  Term........................................................... 25
Section 7.2.  Termination Prior to the Traffic Transfer Date................. 25
Section 7.3.  Remedies of TMI Prior to TMI Security Discharge Date........... 27
Section 7.4.  Liabilities in Event of Termination............................ 28
Section 7.5.  Purchase Price Prepayment and Liquidated Damages............... 28
Section 7.6.  Procedure Upon Termination..................................... 30
Section 7.7.  Exclusion of Consequential and Punitive Damages................ 30
Section 7.8.  Option of AMSC to Put Interest to TMI.......................... 30
Section 7.9.  Satellite Failure.............................................. 33
Section 7.10.  General Rights and Remedies................................... 35

                                    ARTICLE 8
                                  MISCELLANEOUS

Section 8.1.  Notices........................................................ 35
Section 8.2.  Amendments; No Waivers......................................... 36
Section 8.3.  Expenses....................................................... 36
Section 8.4.  Successors and Assigns......................................... 36
Section 8.5.  Interest on Amounts and Set Off................................ 38

                                      (ii)



<PAGE>


                                                                            Page


Section 8.6.  Governing Law.................................................. 38
Section 8.7.  Dispute Resolution; Arbitration................................ 38
Section 8.8.  Counterparts; Effectiveness.................................... 39
Section 8.9.  Severability.................................................. 40A
Section 8.10.  Cooperation and Further Assurances........................... 40A
Section 8.11.  Entire Agreement............................................. 40A
Section 8.12.  Structure.................................................... 40A
Section 8.13.  No Fiduciary Duties; Other Business Opportunities............ 40A
Section 8.14.  Indemnification.............................................. 40B
Section 8.15.  Export Control Compliance.................................... 40B
Section 8.16.  Regulatory Compliance........................................ 40B
Section 8.17.  Bulk Sales Act (Ontario)..................................... 40B
Section 8.18.  AMSC Parent Corp. Joint and Several Liability................ 40C


                             SCHEDULES AND EXHIBITS

Schedule 1.1         Permitted Transferees
Schedule 3.2(1)      Technical and Operating Matters
Schedule 3.2(2)      Telesat Procedures
Schedule 4.1(2)      Allotted Usage
Schedule 4.4(1)      Excess Capacity and Pricing
Schedule 4.4(3)      Restoral Capacity
Schedule 5.2(1)      Amendment to Satellite Capacity Agreement
Schedule 5.4         Form of Press Release
Schedule 6.1(c)      Documents Relating to the Condition of the Shared Satellite
Schedule 6.1(f)      Existing Liens on Shared Satellite

Exhibit A            Form of Conveyance Agreement
Exhibit B            Form of Security Agreement














                                      (iii)


<PAGE>


                          SATELLITE PURCHASE AGREEMENT

     Satellite  purchase  agreement  dated as of  December  2, 1997  between TMI
COMMUNICATIONS  AND  COMPANY,   LIMITED  PARTNERSHIP  ,  a  limited  partnership
organized under the laws of the Province of Quebec, with its principal executive
office  in the City of  Gloucester,  Province  of  Ontario  and AMSC  SUBSIDIARY
CORPORATION,  a corporation dually  incorporated under the laws of the States of
Delaware and  Virginia,  respectively,  with its principal  executive  office in
Reston,  Virginia (and a wholly-owned  subsidiary of American  Mobile  Satellite
Corporation),  and,  solely  for  purposes  of  Section  8.18,  American  Mobile
Satellite Corporation, a Delaware Corporation.

     WHEREAS:

     A. TMI  operates  a  communications  system  for the  provision  of  mobile
satellite services in Canada;

     B. AMSC  operates  a  communications  system  for the  provision  of mobile
satellite services in the United States;

     C. AMSC and  Telesat  Mobile  Inc.  have  heretofore  executed a  Satellite
Capacity  Agreement for the purpose,  inter alia, of establishing  the terms and
conditions for the provision of satellite  capacity by either party to the other
in certain circumstances; and

     D. AMSC has  offered to  purchase a 50%  undivided  interest  in the Shared
Satellite owned by TMI, and to jointly own and operate the Shared Satellite with
TMI to meet the satellite capacity demands of their respective customers, and to
amend  (and,  under  certain  conditions,   terminate)  the  Satellite  Capacity
Agreement  in a  manner  consistent  with  such  joint  ownership,  all as  more
particularly set forth in this Agreement;

     NOW, THEREFORE, in consideration of the mutual agreements contained in this
Agreement,   and  other  good  and  valuable   consideration  (the  receipt  and
sufficiency of which are hereby acknowledged by each of the parties hereto), the
parties hereto agree as follows:


                                    ARTICLE 1
                                 INTERPRETATION

     Section 1.1.  Definitions.  (1) As used in this  Agreement and the recitals
hereto, the following terms have the following meanings:

     "Affiliate"  means,  with  respect to any Person,  any Person  controlling,
controlled  by or under common  control with such Person;  provided that neither
party  hereto  shall  by  reason  of  entering  into  this   Agreement  and  the
consummation  of the  transactions  contemplated  hereby be an  Affiliate of the
other party or of the entity or entities,  if any, through which the other party
holds its Interest. For purposes hereof, the term "control" (including the terms
"controlling,"  "controlled  by" and  "under  common  control  with")  means the
possession, direct or indirect, of the power to direct or cause the direction of
the management and policies of a Person, whether through the ownership of voting
securities, by contract, or otherwise.

     "Agreement"  means this  satellite  purchase  agreement and all  schedules,
exhibits and instruments in amendment or confirmation of it; and the expressions
"Article"  and  "Section"  followed by a number mean and refer to the  specified
Article or Section of this Agreement.

     "AMSC" means AMSC Subsidiary Corporation, a corporation dually incorporated
under the laws of the States of Delaware  and  Virginia,  respectively,  and its
successors and permitted assigns in accordance with the terms of this Agreement.

     "AMSC  Parent  Corp."  means  American  Mobile  Satellite  Corporation,   a
corporation  incorporated  under  the  laws of the  State of  Delaware,  and its
successors.

     "AMSC  Satellite"  means the satellite  owned by AMSC as of the date hereof
(and referenced as the MSAT-2 (M2) satellite).

     "AMSC Satellite  Contract" means the agreement between AMSC, as lessor, the
AMSC Satellite Lessee, and AMSC Parent Corp., as guarantor of the obligations of
AMSC, providing for the lease of the AMSC Satellite.

     "AMSC Satellite Lessee" means African Continental  Telecommunications Ltd.,
and its successors and assigns under the AMSC Satellite Contract.

     "Bankruptcy  Event"  with  respect  to a  Person  means  (i) the  voluntary
commencement  of any  proceeding,  or  voluntary  filing,  by such  Person  of a
petition seeking liquidation,  reorganization,  arrangement or readjustment,  in
any form,  of its debts  under  Title 11 of the United  States Code or under the
Bankruptcy and Insolvency Act (Canada) or under the Winding-Up and Restructuring
Act  (Canada) or under the  Companies'  Creditors  Arrangement  Act (Canada) (or
corresponding  provisions  of future laws of the United  States or of Canada) or
under any other  jurisdiction's  insolvency,  liquidation  or similar laws (each
such United States,  Canadian and other jurisdictions' laws being referred to as
a  "Bankruptcy  Law"),  or such  Person's  filing of an answer  consenting to or
acquiescing  in any such  petition;  or (ii) the  making  by such  Person of any
general  assignment  for the benefit of its  creditors or the  admission by such
Person in writing of its inability to pay its debts as they mature; or (iii) the
consent by such  Person to the filing of, the  failure by such Person to contest
successfully with respect to, or the granting of an order of relief with respect
to (x) any involuntary  petition or application under any Bankruptcy Law seeking
an  application  for  the  appointment  of  a  receiver,   trustee,   custodian,
sequestrator  or  similar  official  for the assets of such  Person,  or (y) any
involuntary   petition  or   application   under  any   Bankruptcy  Law  seeking
liquidation, reorganization,  arrangement or readjustment of its debts under any
Bankruptcy  Law;  or (iv) the  appointment  of a receiver,  trustee,  custodian,
sequestrator  or  similar  official  for the  assets  of such  Person  under any
Bankruptcy Law or otherwise.

     "Business Day" means a day which is not a Saturday, Sunday or legal holiday
on which  commercial  banking  institutions  in New York,  New York or Montreal,
Quebec are authorized to close.

     "Collateral"  means the subject  matter of the TMI Purchase  Money Security
Interest, including the Interest of AMSC and proceeds thereof.

     "CMIS Contract" means the agreement dated as of the date hereof between TMI
and  AMSC  providing  for a  license  from  TMI to  AMSC  in  respect  of  TMI's
CMIS/Eclipse software.

     "Drift Orbit Services  Agreement"  means the agreement dated as of the date
of this  Agreement  between AMSC and Telesat in respect of drift orbit  services
for the AMSC Satellite, as amended, supplemented, restated or modified from time
to time.

     "Enforcement  Notice"  means a  notice  which  may be given by TMI to AMSC,
whenever the Purchase Money Security Interest has become  enforceable,  that TMI
intends to exercise or enforce any remedy  which it may have  against AMSC under
the Security Agreement.

     "Enforcement  Period"  means the period  commencing on the date which is 30
days following the delivery of the Enforcement Notice.

     "Force Majeure" means any acts of God; meteors;  fire, flood,  weather,  or
other catastrophes;  other circumstances in the space environment over which the
parties have no control;  any laws of any governmental  agency or body, national
emergencies,  insurrections,  riots, embargoes, wars, or strikes, lockouts, work
stoppages or other labour difficulties.

     "Interest"  means,  with  respect  to TMI or AMSC,  respectively  (or their
respective  successors or permitted assigns in accordance with the terms of this
Agreement),  its 50%  undivided  ownership  interest  in the  Shared  Satellite,
including  its rights and  obligations  under this  Agreement  in respect of the
Shared Satellite.

     "Lien"  means,  with  respect to any asset,  any  mortgage,  lien,  pledge,
charge, security interest or encumbrance of any kind.

     "Permitted  Liens"  means,  with  respect to any  Person,  undetermined  or
inchoate liens,  privileges and charges  incurred and incidental to the ordinary
course of business  which  arise  solely by  operation  of law and have not been
filed  pursuant  to law against  such  Person or its assets and which  relate to
obligations which are not delinquent.

     "Permitted  Transferee" means, with respect to TMI and AMSC,  respectively,
any of the Persons set forth under its name on Schedule 1.1.

     "Person" means an individual, corporation, partnership, association, trust,
limited  liability  company or any other  entity or  organization,  including  a
court,   a  government  or  political   subdivision   or  an  agency,   unit  or
instrumentality thereof.

     "PIP  Contracts"  means,  collectively,  (i) MSAT  Spacecraft  Contract No.
C90TM0001  dated  December  10,  1990  (and  amendments  thereto)  between  Spar
Aerospace Limited and TMI; and (ii) MSAT Spacecraft Contract No. A90TM0002 dated
December  10,  1990  (and  amendments   thereto)  among  Hughes   Communications
International,  Inc.,  Spar Aerospace  Limited and TMI, in each case as amended,
supplemented or modified from time to time.

     "Relocated  Orbital  Position"  means the  geostationary  orbital  position
located at 101o West longitude or such other nearby  orbital  position as may be
required for satellite coordination for the Shared Satellite.

     "Revenue  Adjustment  Amounts"  means,  collectively,  each  Lease  Revenue
Adjustment  and each Sale Revenue  Adjustment  which become payable to TMI under
Sections 2.2(2) and 2.2(3).

     "Satellite  Capacity  Agreement"  means the  memorandum  of  agreement  for
satellite capacity dated as of February 17, 1992 between AMSC and Telesat Mobile
Inc., as assigned to and assumed by TMI, and as amended,  modified,  restated or
supplemented from time to time.

     "Satellite  Failure"  means at any time  that one or more of the  following
events has  occurred  and is  unremedied  at such  time:  (i)  physical  loss or
destruction of the Shared  Satellite;  (ii) inability of the Shared Satellite to
respond to commands from the Shared Satellite  operator;  (iii) inability of the
Shared  Satellite to maintain its orbital  position or attitude  with respect to
the earth; (iv) loss of 50% or more of the available L Bank RF Power (determined
in accordance  with Schedule  4.1(2)) in either  Hybrid  Matrix  Amplifier;  (v)
reduction in Ku Band EIRP of 3 dB or more;  (vi)  reduction of 3 dB or more in L
Band G/T in any of the four Primary Beams; or (vii) reduction of 3 dB or more in
Ku Band G/T.

     "Satellite  Purchase  Price"  means the amount  equal to sum of the Minimum
Satellite Purchase Price and the Revenue Adjustment Amounts.

     "Secured  Obligations"  means the  payment  and  performance  of all debts,
liabilities  and  obligations  at any time due or accruing  due and owing by, or
otherwise  payable  by,  AMSC  to TMI  under  this  Agreement  or  the  Security
Agreement.

     "Security  Agreement"  means  a  security  agreement  to be made by AMSC in
favour of TMI pursuant to which TMI reserves,  and AMSC grants, the TMI Purchase
Money Security  Interest as security for the Secured  Obligations in the form of
Exhibit B.

     "Shared  Satellite"  means the satellite owned by TMI as of the date hereof
(and is referenced as the MSAT-1 (M1) satellite).

     "Technical  and Operating  Matters" means all matters of the type described
in Schedule 3.1(1).

     "Telesat" means Telesat Canada, a Canadian corporation.

     "Telesat  Agreement"  means the operations  agreement  dated March 24, 1993
between Telesat and Telesat Mobile Inc., as amended by amending  agreement no. 1
dated July 18, 1994 and by amending agreement no. 2 dated September 26, 1995.

     "TMI" means TMI Communications and Company, Limited Partnership,  a limited
partnership  organized  under  the  laws  of the  Province  of  Quebec,  and its
successors and permitted assigns in accordance with the terms of this Agreement.

     "TMI Payment  Account"  means at any time the account of TMI  maintained by
The Toronto Dominion Bank at its branch at 106 Sparks Street,  Ottawa,  Ontario,
branch no. 32326 with account no.  7300269,  ABA 026003243 or such other account
as the chief  financial  officer of TMI may  designate in writing  prior to such
time by notice to AMSC.

     "TMI Purchase Money Security  Interest"  means the  reservation  out of the
transfer by TMI of a 50% undivided  ownership  interest in the Shared Satellite,
and the grant by AMSC, of a first priority  security interest in AMSC's Interest
and the  proceeds  thereof all as more  particularly  set forth in the  Security
Agreement.

     "TMI Security  Discharge  Date" means the first to occur of (i) at any time
prior to the  commencement of the Enforcement  Period,  the date upon which AMSC
shall have indefeasibly paid to TMI the Minimum Satellite Purchase Price in full
together  with all TT&C Fees then owing under this  Agreement  as at the date of
payment  in full of the  Minimum  Satellite  Purchase  Price;  (ii) at any  time
following the  commencement of the Enforcement  Period,  the date upon which TMI
shall have been indefeasibly paid in full the Secured Obligations; and (iii) the
date of the transfer of AMSC's Interest to TMI in accordance with Section 7.8.

     "Traffic  Transfer  Date"  means the date  stipulated  by AMSC  pursuant to
Section  2.4 (or such  later date as AMSC and TMI may agree) as of which each of
the conditions set forth in Section 2.5 and 2.6 has been satisfied (or waived by
the party entitled to waive such  condition) and as of which AMSC will acquire a
50%  undivided  ownership  interest in the Shared  Satellite  subject to the TMI
Purchase Money Security Interest.

     "TT&C"  means  tracking,   telemetry  and  control  services,  drift  orbit
operations and/or other operational services in connection with a satellite.

     "TT&C Fees" means, collectively,  (i) the daily and monthly fees payable to
TMI by AMSC  pursuant  to Section  3.1(2);  and (ii) such  other  amounts as the
parties agree are payable pursuant to Section 3.1(3).

     "U.S.  Base Rate" means,  at any time, the rate of interest per annum equal
to the per annum rate of interest which  National Bank of Canada  announces from
time to time as the reference rate of interest for loans in U.S.  dollars to its
Canadian  borrowers,  adjusted  automatically with each change in such rate, all
without the necessity of any notice to any Person.

     (2) Each of the  following  terms  is  defined  in the  Section  set  forth
opposite such term: 

<TABLE>
<CAPTION>

Term                                                    Section
- ----                                                    -------

<S>                                                     <C>   
AAA                                                     8.7(2)
AAA Rules                                               8.7(2)
AMSC Collateral Agent                                   8.4(2)
AMSC Secured Lenders                                    8.4(2)
Agents                                                  5.4(1)
Allotted Usage                                          4.1(2)
Arbitration Demand                                      8.7(3)
Claimant                                                8.7(2)
Confidential Information                                5.4(1)
Contracting Party                                       5.8
Conveyance                                              2.1
Damages                                                 8.14
Dispute                                                 8.7(1)
Excess Capacity                                         4.4(1)
Excess Coverage                                         4.3(4)
Existing Obligations                                    5.4(1)
GE Spacecraft                                           3.6
Indemnitee                                              8.14
Indemnitor                                              8.14
Information                                             6.1(h)
Joint Operating Agreement                               5.2(2)
Joint Ownership                                         3.01(a)(ii)
Lease Revenue Adjustment                                2.2(2)
Losses                                                  4.7(d)
Minimum Satellite Purchase Price                        2.1
Mountain Beam Settlement                                6.1(h)
Percentage Insurance Interest                           4.3(3)
Purchase Price Prepayment                               2.2(a)
Put Notice                                              7.8(2)
Put Payment                                             7.8(1)
Representative                                          3.2(1)
Respondent                                              8.7(3)
Sale Revenue Adjustment                                 2.2(3)
Satellite Failure Notice                                7.9(1)
Satellite Failure Payment                               7.9(1)
Satellite Insurance                                     4.3(2)
Satellite Performance                                   6.1(h)
Services Operating Committee                            3.2(1)
Specified Time Period                                   4.4(1)
Technical and Operating Matters                         3.2(1)
Telesat Procedures                                      3.2(2)
Temporary Testing Right                                 4.7
Term                                                    7.1
TMI Existing Liens                                      6.1(f)
Uninsured Amount                                        4.3(2)
</TABLE>


     Section 1.2.  Gender and Number.  Any reference in this Agreement to gender
includes all genders and words  importing  the singular  number only include the
plural and vice versa.

     Section  1.3.  Headings,  etc. The  provision  of a Table of Contents,  the
division of this  Agreement  into  Articles and  Sections  and the  insertion of
headings  are  for  convenient   reference  only  and  are  not  to  affect  the
interpretation of this Agreement.

     Section 1.4. Currency. All references in this Agreement to dollars,  unless
otherwise  specifically  indicated,  are expressed in the currency of the United
States of America.

     Section 1.5.  Certain  Phrases,  etc. In this  Agreement  (i) (y) the words
"including" and "includes" mean "including (or includes) without limitation" and
(z) the phrase "the  aggregate of", "the total of", "the sum of", or a phrase of
similar  meaning means "the  aggregate (or total or sum),  without  duplication,
of", and (ii) in the  computation  of periods of time from a specified date to a
later specified date, unless otherwise  expressly stated,  the word "from" means
"from  and  including"  and  the  words  "to"  and  "until"  each  mean  "to but
excluding".

     Section 1.6.  Incorporation  of Schedules.  The schedules  attached to this
Agreement  shall,  for all purposes of this Agreement,  form an integral part of
it.

     Section 1.7.  Certificates.  Any certificate  required by the terms of this
Agreement  to be given by any officer of either  party for and on behalf of such
party shall be given  without any personal  liability on the part of the officer
giving the certificate.


                                    ARTICLE 2
                    SALE OF 50% INTEREST IN SHARED SATELLITE

     Section 2.1. Sale of 50% Interest in Shared Satellite. Subject to the terms
and  conditions of this  Agreement,  TMI agrees to sell,  assign and transfer to
AMSC, and AMSC agrees to purchase from TMI on the Traffic  Transfer  Date,  good
and  marketable  title  to a 50%  undivided  ownership  interest  in the  Shared
Satellite,  free and  clear of all  Liens,  except  for and  subject  to the TMI
Purchase Money Security  Interest,  for an aggregate  amount equal to the sum of
(x) U.S.$60,000,000 (the "Minimum Satellite Purchase Price") and (y) the Revenue
Adjustment  Amounts.  The  transfer  shall be effected  pursuant to a conveyance
agreement in the form attached as Exhibit A (the "Conveyance").

     Section 2.2.  Satellite  Purchase Price.  (1) Except as otherwise  provided
under Sections 7.3, 7.8 and 7.9, the Minimum  Satellite  Purchase Price shall be
paid by AMSC to TMI as follows:

(a) on the date of this Agreement,  the amount of U.S.$5,000,000  (the "Purchase
Price Prepayment");

(b) on the Traffic Transfer Date, the amount of U.S.$3,000,000; and

(c) the amount of U.S.$52,000,000  shall be paid in equal quarterly  instalments
of U.S.$3,000,000,  the first instalment to be due and payable on the date which
is three months  following the Traffic  Transfer Date and each instalment  after
that date to be due and  payable  on the date which is three  months  thereafter
until the Minimum Satellite Purchase Price has been paid in full.

     (2) At any time and from time to time that AMSC receives  payments from the
AMSC Satellite Lessee (or any subsequent lessee of, or transferee of an interest
in, the AMSC Satellite) pursuant to the AMSC Satellite Contract (or any renewal,
extension, substitution or replacement thereof) in an aggregate amount in excess
of  U.S.$190,000,000,  then  AMSC  shall  pay to TMI,  and  there  shall  become
immediately due and payable, an amount (each a "Lease Revenue Adjustment") equal
to twelve thirty-eighths (12/38ths) of all such excess amounts; and

     (3) At any time and from time to time that AMSC receives  proceeds upon any
sale or  other  disposition  of the  AMSC  Satellite  which  together  with  the
aggregate amount of all payments received from the AMSC Satellite Lessee (or any
subsequent  lessee of, or  transferee  of an  interest  in, the AMSC  Satellite)
pursuant to the AMSC Satellite Contract (or any renewal, extension, substitution
or  replacement  thereof)  in an  aggregate  amount  in excess of the sum of (x)
U.S.$190,000,000  and (y) thirty-eight  twelfths (38/12ths) of all Lease Revenue
Adjustments  received by TMI pursuant to Section 2.2(2),  then AMSC shall pay to
TMI, and there shall become immediately due and payable, an amount (each a "Sale
Revenue Adjustment") equal to one-half (2) of all such excess proceeds;

     (4) Each Lease Revenue Adjustment and each Sale Revenue Adjustment shall be
paid to TMI immediately upon receipt thereof by AMSC but the calculation of such
amounts (i) shall be net of any bona fide costs and expenses incurred by AMSC in
connection  with such additional  payments or proceeds,  as the case may be; and
(ii) shall be in respect  of the sale or the lease of, or other  transfer  of an
interest in, the AMSC  Satellite only and shall exclude any revenues or proceeds
attributable to ground systems, licensing or other related revenue.

     (5)  AMSC may  prepay  at any time the  Minimum  Satellite  Purchase  Price
without premium or penalty.

     (6) At any time prior to the  commencement of the Enforcement  Period,  TMI
will  discharge  the TMI Purchase  Money  Security  Interest  upon  indefeasible
payment in full of the Minimum Satellite  Purchase Price and all TT&C Fees owing
as at the date of payment in full of the Minimum Satellite Purchase Price and at
the request and expense of AMSC.

     (7) For the purposes of verifying  the  calculation  of Revenue  Adjustment
Amounts or the amounts payable by AMSC under Section 7.9(5),  AMSC shall provide
TMI,  within five  Business  Days (or such  longer  period as is  reasonable  to
respond in the  circumstances)  of any  request by TMI  therefor,  with true and
complete copies of the books, records, invoices and contracts of AMSC evidencing
or relating to  payments  received  under the AMSC  Satellite  Contract  (or any
renewal,  extension,  substitution  or repayment  thereof) and any sale or other
disposition of the AMSC Satellite and the proceeds thereof, as needed for TMI to
evaluate the application of Section 2.2 or 7.9(5).

     Section 2.3. Satellite  Purchase Price and Prepayment.  (1) Each of TMI and
AMSC acknowledges and agrees that:

(a) on and after the Traffic  Transfer  Date and the  completion of the transfer
specified in Section 2.1 and except as otherwise provided under Sections 7.8 and
7.9, the Satellite Purchase Price and the TT&C Fees shall be payable in each and
every event and  circumstance  including  Force  Majeure,  failure of the Shared
Satellite or any part thereof,  revocation or termination of any  authorization,
license,  approval or consent  required to  relocate,  use or operate the Shared
Satellite and the relocation of the Shared Satellite; and

(b) TMI has entered into this Agreement on the condition that subject only
to the repayment of the Purchase  Price  Prepayment  in accordance  with Section
7.5, the Purchase Price Prepayment shall be irrevocable and non-refundable.

     (2) All  payments  of the  Satellite  Purchase  Price,  TT&C Fees and other
amounts owing by AMSC hereunder shall be made to the TMI Payment Account by wire
transfer in immediately  available  funds prior to 2:00 p.m.  (Montreal time) on
the payment date. If any payment to be made under this Agreement is stated to be
due on a day which is not a Business Day, the due date shall be the  immediately
preceding Business Day.

     Section 2.4. Closing on Traffic Transfer Date. AMSC shall give TMI at least
10 Business Days prior written  notice (or such shorter  period as TMI may agree
in writing) of the  proposed  Traffic  Transfer  Date which shall be a date upon
which AMSC believes, acting reasonably,  the conditions to the sale by TMI under
Section 2.5 will be capable of performance or satisfaction, as the case may be.

     Section  2.5.  Conditions  to Traffic  Transfer  Date and Sale by TMI.  The
occurrence of the Traffic  Transfer  Date, and the obligation of TMI to sell the
50% undivided  ownership  interest in the Shared Satellite,  shall be subject to
the fulfilment of the following  conditions precedent (or waiver thereof by TMI)
at or prior to the Traffic Transfer Date:

(a) TMI shall have  received the Security  Agreement  executed and  delivered by
AMSC;

(b) TMI shall  receive in the TMI Payment  Account  the  partial  payment of the
purchase  price  specified  in  Section  2.2(b) and the TT&C Fees  specified  in
Section 3.1(2)(a);

(c) TMI shall have obtained (or satisfied in the case of any applicable  waiting
period) all  Canadian  governmental  consents  and  approvals  required by it to
relocate the Shared  Satellite to the Relocated  Orbital  Position and all other
consents  and  approvals  specified in Section  6.1(e)(iii)(y);  AMSC shall have
obtained  (or  satisfied  in the  case of any  applicable  waiting  period)  all
American  governmental  consents and  approvals  required to relocate the Shared
Satellite to the Relocated  Orbital  Position and to relocate the AMSC Satellite
to a new orbital slot over or near the  continent of Africa;  and TMI shall have
received a  certificate  signed by the chief  executive  officer of AMSC on such
date  confirming  that all such consents and approvals have been so obtained (or
waiting periods satisfied, as the case may be);

(d) AMSC shall have  performed in all material  respects all of its  obligations
hereunder  required to be  performed  by it on or prior to the Traffic  Transfer
Date,  the  representations  and warranties of AMSC contained in Article 6 or in
any certificate or other writing delivered  pursuant hereto shall be true in all
material  respects on each of the date hereof and the Traffic  Transfer Date, in
each  case as if made on and as of such  date  (except  as  otherwise  expressly
stated in the subject  representation  and warranty as being made as of the date
of this Agreement,  the Traffic Transfer Date or another specific date); and TMI
shall have  received a  certificate  on the Traffic  Transfer Date signed by the
chief executive officer of AMSC to the foregoing effect;

(e) TMI shall have received  legal  opinions,  in form and substance  reasonably
satisfactory  to TMI,  (i)  from  AMSC in house  counsel,  as to  execution  and
delivery by AMSC and AMSC Parent  Corp.  of this  Agreement  and, in the case of
AMSC, the Security  Agreement,  the corporate authority and capacity of AMSC and
AMSC Parent Corp.  to enter into this  Agreement  and, in the case of AMSC,  the
Security  Agreement;  (ii) from outside Ontario counsel as to the enforceability
of this Agreement  against AMSC and AMSC Parent Corp. and the  enforceability of
the Security  Agreement against AMSC; and (iii) from outside local counsel as to
the validity and  perfection of the Security  Agreement in the  jurisdiction  in
which the chief executive office of AMSC is located, and as to perfection of the
Security  Agreement  in  Washington  D.C.,  the  Province  of  Ontario  and each
jurisdiction  from which signals from a feeder link earth station are or, to the
knowledge of AMSC, will be transmitted to the Shared Satellite;

(f) TMI shall have received  evidence of registration of the Security  Agreement
(or notices or financing  statements in respect  thereof) in the jurisdiction in
which the  chief  executive  office of AMSC is  located,  Washington  D.C.,  the
Province of Ontario and each  jurisdiction from which signals from a feeder link
earth  station are or, to the  knowledge  of AMSC,  will be  transmitted  to the
Shared Satellite;

(g) TMI shall have  received  from each creditor of AMSC holding a Lien upon any
part of the Collateral,  an agreement that such creditor's  rights and interests
in and to the  collateral  pledged to such creditor under the Lien granted to it
by AMSC is subject to the  provisions  of this  Agreement,  and an  agreement to
postpone and subordinate such creditor's Lien to the TMI Purchase Money Security
Interest, in form and substance reasonably satisfactory to TMI; and

(h) TMI shall  have  received  a true and  complete  copy of the AMSC  Satellite
Contract and a certificate executed by the President of AMSC which confirms that
(w) TMI has received a true and complete  copy of the AMSC  Satellite  Contract,
(x) the AMSC Satellite  Contract is a legal, valid and binding agreement of AMSC
and the AMSC Satellite  Lessee  enforceable in accordance with its terms subject
to the  effect  of any  applicable  Bankruptcy  Law or  similar  laws  affecting
creditors'  rights generally and the discretion that a court may exercise in the
granting of equitable remedies,  (y) the AMSC Satellite Contract remains in full
force and effect as of the  Traffic  Transfer  Date,  and (z) AMSC has  received
payment from the AMSC  Satellite  Lessee of all amounts due and owing as of such
date.

     Section 2.6.  Conditions to Traffic Transfer Date and Purchase by AMSC. The
occurrence  of the Traffic  Transfer  Date shall be further  subject to, and the
obligation  of AMSC to  purchase  the 50%  undivided  ownership  interest in the
Shared Satellite shall be subject to, the fulfilment of the following conditions
precedent (or waiver thereof by AMSC) at or prior to the Traffic Transfer Date:

(a) AMSC shall have obtained (or satisfied in the case of any applicable waiting
period) all American  governmental  consents and approvals  required to relocate
the Shared Satellite to the Relocated  Orbital Position and to relocate the AMSC
Satellite to a new orbital slot over or near the continent of Africa;  TMI shall
have obtained (or satisfied in the case of any  applicable  waiting  period) all
Canadian  governmental  consents  and  approvals  required by it to relocate the
Shared  Satellite to the Relocated  Orbital  Position and all other consents and
approvals  specified in Section  6.1(e)(iii)(y);  and AMSC shall have received a
certificate signed by the chief executive officer of TMI on such date confirming
that all such consents and approvals  have been so obtained (or waiting  periods
satisfied, as the case may be);

(b) TMI shall have  performed  in all material  respects all of its  obligations
hereunder  which are  required to be  performed by it on or prior to the Traffic
Transfer Date, the  representations and warranties of TMI contained in Article 6
or in any certificate or other writing  delivered  pursuant hereto shall be true
in all  material  respects on each of the date  hereof and the Traffic  Transfer
Date,  in each  case as if made on and as of  such  date  (except  as  otherwise
expressly stated in the subject  representation and warranty as being made as of
the date of this Agreement, the Traffic Transfer Date or another specific date);
and AMSC shall have received a certificate  on the Traffic  Transfer Date signed
by the chief executive officer of TMI to the foregoing effect;

(c) AMSC shall have received the Conveyance executed and delivered by TMI;

(d) AMSC shall have received legal  opinions,  in form and substance  reasonably
satisfactory to it, (i) from TMI's in house counsel as to execution and delivery
by the  general  partner  of  TMI,  in the  name  and on  behalf  of TMI of this
Agreement and the  Conveyance  and the  corporate  authority and capacity of the
general  partner of TMI to enter into this  Agreement and the  Conveyance in the
name and on  behalf  of TMI and (ii)  from  outside  Ontario  counsel  as to the
enforceability of this Agreement and the Conveyance against TMI; and

(e) AMSC shall have received  evidence  satisfactory  to it, acting  reasonably,
that the  undivided  50%  interest in the Shared  Satellite to be conveyed to it
under  this  Agreement  and  the  Conveyance  is free  and  clear  of any  Liens
registered  against  TMI or its  assets  under the  personal  property  security
registers of the Provinces of Ontario and Quebec including TMI Existing Liens.


                                    ARTICLE 3
                      TT&C AND SERVICES OPERATING COMMITTEE

     Section 3.1. TT&C Fees. (1) AMSC and TMI acknowledge and agree that Telesat
currently  provides and will continue to provide  following the Traffic Transfer
Date TT&C services for the Shared Satellite pursuant to the Telesat Agreement.

     (2) In  consideration  of the  payment  by TMI of all  such  TT&C  services
provided by Telesat in respect of the Shared  Satellite,  AMSC shall pay to TMI,
and there shall become due and payable:

(a) on the  Traffic  Transfer  Date,  an amount  equal to the product of (i) the
number of days  remaining  in the calendar  month in which the Traffic  Transfer
Date occurs (including the Traffic Transfer Date), and (ii) U.S.$3,333; and

(b) on the  first  Business  Day of  each  calendar  month,  during  the  period
commencing  on the  first  calendar  month  immediately  following  the  Traffic
Transfer Date and ending on the  decommissioning  of the Shared  Satellite or at
such  time as  Telesat  ceases  to  provide  the TT&C  services  for the  Shared
Satellite, the amount of U.S.$100,000.

     (3) Upon the expiry of the Telesat  Agreement in accordance  with its terms
and the election by TMI to renew,  extend or replace the Telesat Agreement,  TMI
and AMSC shall  negotiate  in good faith to fairly  determine  the amount of the
TT&C fees and  expenses  to be payable by AMSC under such  renewed,  extended or
replaced TT&C agreement taking into account the then existing circumstances.

     Section 3.2.  Services  Operating  Committee.  (1) On or before the Traffic
Transfer Date, the parties shall establish a committee (the "Services  Operating
Committee")  consisting of four members (each a  "Representative"),  two of whom
shall be appointed  by TMI and two of whom shall be  appointed by AMSC.  Each of
TMI and AMSC may at any time and from  time to time,  by  written  notice to the
other party, replace any one or both of the Representatives appointed by it, and
any person so replaced  shall cease to be a  Representative  and a member of the
Services Operating  Committee upon the giving of such notice.  During the period
commencing on the Traffic  Transfer Date and ending on the expiry of the Term of
this  Agreement,  the Services  Operating  Committee  shall manage or direct all
technical and operating  matters in respect of the Shared  Satellite,  including
determination  of  power  capacity  and  capacity  usage  and  related  spectrum
considerations,    traffic   planning,    access   engineering,    interference,
troubleshooting,  satellite reconfiguration, satellite health considerations and
matters  related  to TT&C  services  as well as the other  matters  set forth in
Schedule 3.2(1) (" Technical and Operating Matters").  In managing and directing
Technical and Operating  Matters,  the parties  shall apply the  principles  set
forth in such Schedule 3.2(1).  Except as otherwise  provided in Sections 3.2(4)
and  7.3(2),  all  decisions  or  actions  to be made or taken  by the  Services
Operating  Committee  shall  require  the  unanimous  agreement  of  all  of the
Representatives,  and each of TMI and AMSC  agrees  to use its  reasonable  best
efforts to cause the Representatives  appointed by it to negotiate in good faith
to  resolve  all  matters  that are within  the scope of  responsibility  of the
Services Operating Committee.  If, notwithstanding the good faith efforts of the
Representatives to resolve any such matter, the Services Operating  Committee is
unable to reach  unanimous  agreement  with respect to any such matter  within a
reasonable  period of time,  the Services  Operating  Committee  shall refer the
disputed matter to the respective Chief Executive  Officers of TMI and AMSC, who
shall attempt to resolve the disputed  matter in accordance with Section 8.7(1),
and if the disputed matter is not so resolved,  then either party may submit the
disputed  matter  to  arbitration  in  accordance  with  Sections  8.7(2) to (7)
inclusive.

     (2)  Technical  and  Operating  Matters  relating  to TT&C  services  to be
provided  by  Telesat  shall be  conducted  in  accordance  with  the  operating
procedures  referred to in Schedule  3.2(2) (the "Telesat  Procedures")  (taking
into account any Technical and Operating Matters that are particularly  relevant
to the Shared Satellite). The Services Operating Committee may amend the Telesat
Procedures  (in  accordance  with  any  procedures  set  forth  in  the  Telesat
Agreement) or establish and adopt  additional  operating  procedures for matters
other than those relating to TT&C matters covered by the Telesat Agreement.  The
Services Operating Committee shall be responsible for monitoring compliance with
the Telesat Procedures (as amended or supplemented from time to time as provided
above);  provided that the parties may agree to delegate such  responsibility to
Telesat or another third party operator.

     (3) The Services Operating Committee shall promptly  establish,  and at all
times  maintain,  an on-call  roster,  on an alternating  monthly basis,  of TMI
delegated personnel and AMSC delegated personnel,  respectively, who shall be on
call to make emergency  decisions on matters  affecting the health of the Shared
Satellite not covered by the Telesat  Procedures.  Except as otherwise  provided
under Section  7.3(2),  the parties intend and agree that the single person then
designated  from TMI's on-call  roster,  acting alone, is authorized to make all
such  emergency  decisions  during the first  month,  commencing  on the Traffic
Transfer  Date, and that the single person then  designated  from AMSC's on-call
roster,  acting alone, is authorized to make all such emergency decisions during
the next succeeding  month, and so on,  alternating each month from the parties'
respective on-call rosters.

     (4) In the  event  the  Services  Operating  Committee  is  unable to reach
unanimous agreement with respect to any Technical and Operating Matter necessary
to  safeguard  the health of the  Shared  Satellite,  then until such  unanimous
agreement is reached or such matter has been  resolved  pursuant to Section 8.7,
TMI shall have the sole and  exclusive  right to issue to Telesat all  commands,
directions  and  instructions  as are  necessary to safeguard  the health of the
Shared  Satellite.  AMSC and TMI shall cooperate with each other during any such
period of dispute and shall provide Telesat with all data and other  information
as may be required.

     Section 3.3. Quarterly  Reporting.  Commencing on the Traffic Transfer Date
and ending upon the expiry of the Term of this Agreement,  in order to assist in
effecting the transactions  contemplated  hereunder, no later than 30 days after
the end of each calendar quarter, each of TMI and AMSC will deliver to the other
party hereto a report  showing its monthly  power usage of the Shared  Satellite
determined  in  accordance  with Schedule  4.1(2)(II)  for the calendar  quarter
ending immediately preceding the date such report is delivered together with the
delivering  party's  estimate of its expected  monthly power usage of the Shared
Satellite  for the calendar  quarter  immediately  following  the last  calendar
quarter in respect of which actual results are shown.

     Section 3.4. Performance Anomalies and Incentive Payments.  Each of TMI and
AMSC shall promptly notify the other upon learning of any satellite  performance
anomalies and of the relevant  facts known to it concerning  such anomaly.  AMSC
shall  cooperate  with TMI as may be reasonably  necessary  from time to time to
determine whether any performance  incentive  payments are payable under the PIP
Contracts.  AMSC shall not be responsible for any payments to the  manufacturers
of the Shared Satellite under the PIP Contracts or otherwise.

     Section 3.5.  Satellite Health Reports.  TMI shall promptly furnish to AMSC
one copy of each  satellite  health report which it receives  from Telesat,  the
manufacturers  of the  Shared  Satellite  or any other  Person in respect of the
Shared Satellite.

     Section 3.6. Radio  Frequencies.  AMSC shall be solely  responsible for any
and all obligations under the agreement dated December 14, 1992 between AMSC and
GTE Spacenet  Corporation,  as amended by the amendment  dated  November 7, 1997
between AMSC and GE American  Communications,  Inc. TMI shall,  in  consultation
with  AMSC,  exercise  reasonable  commercial  efforts  to  operate  the  Shared
Satellite so as to avoid  interference  with any spacecraft owned or operated by
GTE  Spacenet  Corporation  or  GE  American   Communications,   Inc.  (the  "GE
Spacecraft") at or near the Relocated Orbital Position.


                                    ARTICLE 4
                         SATELLITE SHARING ARRANGEMENTS

     Section 4.1.  Effect of Traffic  Transfer  Date.  (1) From the date of this
Agreement  until the Traffic  Transfer  Date, TMI will continue to use and enjoy
the economic benefits and risks of the entire Shared Satellite.

     (2) Effective as of the Traffic Transfer Date, TMI and AMSC will hold their
respective  Interests  in the Shared  Satellite  as tenants in common and not as
joint tenants and will each have a first priority right to use,  without charge,
one-half  of the  capacity  of the Shared  Satellite,  which  capacity  shall be
determined in accordance  with the provisions of Schedule  4.1(2) (the "Allotted
Usage"), on the terms and conditions set forth in this Agreement.

     Section 4.2. Orbital Slots. At any time following the Traffic Transfer Date
AMSC may  request  TMI to, and within 30 days  following  receipt of any written
request  therefor by AMSC,  TMI and AMSC shall,  commence the move of the Shared
Satellite to the Relocated  Orbital  Position.  Upon relocation to the Relocated
Orbital Position,  the bore site of the Shared Satellite shall be fixed at 45.9?
North latitude and 92.3? West longitude. If:

(a) at any time after the  Traffic  Transfer  Date,  AMSC  acquires a new second
generation  satellite (other than the Shared Satellite or the AMSC Satellite) or
the AMSC Satellite is returned to AMSC for whatever reason (and is not resold or
re-leased to a third party); and

(b) the original orbital position of the Shared Satellite located at 106.5o West
longitude is then available;

then,  upon the written request by AMSC, TMI and AMSC shall use their good faith
efforts  to obtain  all  regulatory  consents  necessary  to permit  and,  if so
obtained,  will cause (unless,  taking into account all facts and circumstances,
TMI and AMSC  agree  otherwise),  the Shared  Satellite  to be  returned  to its
original  orbital  position  located at 106.5o West  longitude to permit AMSC to
place the new  satellite  acquired by it or the AMSC  Satellite at the Relocated
Orbital  Position.  All  expenses  associated  with  obtaining  such  regulatory
approvals and with any such move of the Shared Satellite to its original orbital
slot and with any such placement of AMSC's new satellite or the AMSC  Satellite,
shall be borne solely by AMSC.

     Section 4.3.  Insurance.  (1) Each of TMI and AMSC agree that all insurance
proceeds  paid or  payable to TMI under any  insurance  policy in respect of any
event  occurring  prior to the  Traffic  Transfer  Date in respect of the Shared
Satellite  belong  solely and  exclusively  to TMI, and TMI has no obligation to
AMSC in respect thereof.

     (2) On and after the Traffic Transfer Date, TMI and AMSC will each have the
right (but not the obligation), at such party's sole expense, to obtain in-orbit
insurance ("Satellite Insurance") in respect of their respective Interest in the
Shared  Satellite up to 50% of the total  insurable  value (based on  reasonable
commercial  availability)  of the  Shared  Satellite.  If TMI or AMSC  elects to
obtain Satellite Insurance for any twelve month period for less than all or none
of its share of the total insurable value in respect of its respective  Interest
in the Shared  Satellite (as the case may be, the "Uninsured  Amount"),  then it
shall so notify the other party in writing and the other party shall be entitled
to obtain  Satellite  Insurance  for such twelve  month period in respect of the
notifying  party's  Interest in the Shared  Satellite  (in addition to the other
party's share of such total insurable value) up to the Uninsured Amount.

     (3) If both TMI and AMSC elect to obtain Satellite Insurance for any twelve
month  period  and it is  necessary  or  advantageous  to have a  single,  joint
insurance  policy in respect  of the  Shared  Satellite  for such  twelve  month
period,  then each of TMI and AMSC will use all reasonable  efforts to cause the
insurer providing Satellite Insurance on, or in respect of, the Shared Satellite
to issue,  effective as of the  commencement  of and during such  period,  a new
policy (or riders to any existing  insurance policy) naming both TMI and AMSC as
a named  co-insured.  Subject  to the  proviso  in  Section  4.3(4),  after  the
commencement  of such period,  each of TMI and AMSC shall pay that percentage of
all insurance  premiums owed in connection with the Satellite  Insurance for the
Shared Satellite which is provided pursuant to a single,  joint insurance policy
equal to the percentage of Satellite  Insurance obtained by them,  respectively,
in accordance with Section 4.3(2) (a party's "Percentage Insurance Interest").

     (4) On and  after  the  Traffic  Transfer  Date,  to the  extent  that  any
insurance  proceeds become payable under  Satellite  Insurance in respect of the
Shared Satellite which is provided pursuant to a single,  joint insurance policy
in respect of any loss event occurring after the Traffic  Transfer Date, each of
TMI and AMSC shall be entitled to that amount of such  insurance  proceeds equal
to their  respective  Percentage  Insurance  Interests;  provided that if either
party  wishes to obtain  insurance  coverage in excess of 100% of the  insurable
value of the Shared  Satellite (" Excess  Coverage") and such Excess Coverage is
available  and is obtained as part of (or by rider to) the subject  single joint
insurance policy,  then (i) that portion of the insurance  premiums allocable to
such Excess  Coverage shall be borne by the party obtaining such Excess Coverage
and (ii) the parties  shall  divide any  insurance  proceeds  payable or paid in
respect of the total insurance coverage under such single joint insurance policy
in a manner that is  equitable  and  reflects  the pay-out  attributable  to the
respective  Percentage  Insurance  Interests  held by the parties as well as the
Excess  Coverage  held by one or both  parties.  To the extent that proceeds are
distributed to the parties by the insurer  otherwise than in the manner provided
for in this Section 4.3(4),  TMI and AMSC shall make such payments and take such
actions as may be necessary to give effect to the intent of this Section 4.3(4),
and the party who has received a payment in excess of that amount to which it is
entitled  hereunder  shall hold such excess  amount in trust for the other party
and  shall pay such  excess  amount to the  other  party  not later  than  three
Business Days after receipt thereof.

     (5) If required under any joint  constructive  total loss insurance policy,
the parties  shall  execute and deliver all such  instruments,  assignments  and
other  documents as may be required by the insurer to transfer their  respective
interests  in  the  Shared  Satellite  to  the  insurer  in  connection  with  a
constructive total loss under such policy.

     (6) TMI  shall,  upon the  written  request  of AMSC,  provide to AMSC such
technical  information  developed by or furnished  to TMI  regarding  the Shared
Satellite as AMSC may reasonably  request in connection with any attempt by AMSC
to obtain such insurance.

     Section  4.4.  Excess  Capacity;  and  Termination  of  Satellite  Capacity
Agreement.  (1) Effective as of the Traffic  Transfer Date, each party will make
available to the other party, promptly after receipt of a request therefor,  any
excess capacity that such party then has as part of its Allotted Usage and which
is  reasonably  considered  by such party not to be required for its existing or
prospective business ("Excess Capacity");  provided that (i) this Section 4.4(1)
shall be subject to United States and Canadian  governmental or agency rules and
regulations  with  respect  to  priority  and  preemptive  access  in  emergency
situations,  and (ii) in determining its Excess Capacity, a party shall have the
right to specify  the time  period  during  which such  capacity  is  reasonably
expected  not to be required  for its  existing  or  prospective  business  (the
"Specified Time Period").  Unless the parties agree otherwise,  once a party has
allocated  Excess  Capacity to the other party,  (x) the allocating  party shall
thereafter  have no right to use such Excess  Capacity  for the  Specified  Time
Period  except with the consent of the  receiving  party,  and (y) the receiving
party shall  thereafter  be  obligated  to pay for such Excess  Capacity for the
Specified Time Period  without regard to the receiving  party's use or nonuse of
such Excess Capacity. Excess Capacity shall be determined in accordance with the
provisions of Schedule 4.1(2) and the amount to be paid for the  availability of
Excess  Capacity  shall be  determined  in  accordance  with the  provisions  of
Schedule 4.4(1).

     (2) If, as of the Traffic Transfer Date, the Satellite  Capacity  Agreement
(as amended  pursuant to Section  5.2(1)) has not been  terminated in accordance
with its terms,  then  effective as of the Traffic  Transfer Date, the Satellite
Capacity  Agreement (as so amended) shall be deemed  suspended and,  without any
further  action by the parties,  shall not be operative  or  enforceable  by the
parties thereto.  If, following such deemed suspension of the Satellite Capacity
Agreement,  this Agreement is terminated for any reason,  including  pursuant to
Sections  7.2, 7.8 or 7.9, and the  Satellite  Capacity  Agreement  has not been
terminated in accordance with its terms,  then effective as of such  termination
date,  the  Satellite  Capacity  Agreement  (as so  amended)  shall  cease to be
suspended  without  any  further  action by the  parties and shall be and become
operative and enforceable by the parties thereto.

     (3) The  parties  shall  provide  each  other  with  restoral  capacity  in
accordance with the provisions of Schedule 4.4(3).

     Section  4.5.  Decommissioning  of  Satellite.  At such time as the  Shared
Satellite  has reached the end of its useful  life or upon the  occurrence  of a
constructive total loss within the meaning of any applicable  constructive total
loss  insurance  policy,  TMI shall  cause  Telesat,  at the  expense of TMI, to
decommission  the Shared  Satellite  by removing it from the  Relocated  Orbital
Position to the extent technically possible to do so.

     Section  4.6.  Exclusion of  Liability  for  Telesat.  EACH OF TMI AND AMSC
HEREBY  ACKNOWLEDGE  AND AGREE THAT  TELESAT  SHALL NOT BE LIABLE,  DIRECTLY  OR
INDIRECTLY,  TO TMI, AMSC OR ANY PERMITTED  ASSIGNEES OR SUCCESSOR OWNERS OF THE
SHARED SATELLITE FOR ANY LOSS,  DAMAGE,  LIABILITY OR EXPENSE HOWSOEVER ARISING,
WHETHER  FORESEEABLE OR NOT, WITH RESPECT TO THE PERFORMANCE OR  NON-PERFORMANCE
OR  IMPROPER  PERFORMANCE  OF THE SHARED  SATELLITE  OR ANY PART  THEREOF OR THE
PERFORMANCE  OR  NON-PERFORMANCE  OR IMPROPER  PERFORMANCE  BY TELESAT UNDER THE
TELESAT  AGREEMENT OR ANY ACTS OR OMISSIONS  ASSOCIATED  THEREWITH,  WHETHER THE
BASIS OF LIABILITY IS BREACH OF CONTRACT,  TORT (INCLUDING NEGLIGENCE AND STRICT
LIABILITY), STATUTE OR ANY OTHER LEGAL THEORY EXCEPT AS EXPRESSLY PROVIDED UNDER
THE TELESAT AGREEMENT. AMSC and TMI agree that TMI shall hold the benefit of the
provisions  contained  in this Section as agent and bare trustee for Telesat and
that TMI shall  enforce such  provision in  accordance  with the  directions  of
Telesat.

     Section 4.7.  Temporary  Traffic  Transfer.  Prior to the Traffic  Transfer
Date,  TMI shall,  upon 30 days prior written  notice from AMSC,  permit AMSC to
temporarily transfer its communications  traffic to the Shared Satellite for the
purpose of  enabling  AMSC to perform  such tests on the AMSC  Satellite  as are
necessary  or  desirable  to  confirm  that the AMSC  Satellite  will be able to
provide mobile  satellite  service over the continent of Africa (the  "Temporary
Testing Right").  Such Temporary Testing Right is granted to AMSC subject to the
following terms and conditions:

(a) the  Temporary  Testing Right shall be provided to AMSC free of charge for a
term of no more  than 7 weeks,  or such  longer  period  as may be  required  to
perform the testing contemplated under the Drift Orbit Services Agreement;  upon
completion of the temporary testing, in accordance with TMI's election, prior to
the Traffic  Transfer Date, AMSC will either remove its traffic back to the AMSC
Satellite  or  maintain  the traffic on the Shared  Satellite  until the Traffic
Transfer Date without charge to AMSC. In the event that AMSC does not remove its
traffic from the Shared  Satellite  following the completion of testing upon the
exercise of its  Temporary  Testing  Right and following an election by TMI that
AMSC remove its traffic until the Traffic  Transfer Date, AMSC shall pay TMI, in
advance,  at the  rate of  U.S.$24,109  per  month  (or  portion  thereof,  on a
pro-rated  basis) for each 0.5% of the available  Radio  Frequency (RF) power in
either the North or South Hybrid  Matrix  Amplifier  (as  referenced in Schedule
4.1(2)) so provided;

(b) Telesat  shall have assumed  control of the AMSC  Satellite  pursuant to the
Drift Orbit Services Agreement before AMSC is entitled to exercise the Temporary
Testing Right;

(c) before  transferring  any traffic to the Shared  Satellite,  AMSC shall have
submitted  a  written  traffic  transfer  plan to TMI for  its  approval,  which
approval shall not be unreasonably withheld;

(d) AMSC shall indemnify TMI, its partners, the respective Affiliates of TMI and
such partners and the respective officers,  directors,  employees,  shareholders
and agents of each of the foregoing Persons against,  and agrees to hold each of
them  harmless  from,  any and all  losses,  liabilities,  damages,  claims  and
expenses ("Losses") incurred by them to the extent that such Losses arise out of
any damage or degradation to the Shared  Satellite  caused by AMSC's exercise of
the Temporary Testing Right; and

(e) AMSC  acknowledges  that the  Shared  Satellite  will be made  available  in
connection  with  the  Temporary  Testing  Right on an "as is"  basis,  and AMSC
expressly  excludes  and  disclaims  any  warranty or condition of any kind with
respect  to  the  grant  or  exercise  of the  Temporary  Testing  Right  or the
performance,  nonperformance or improper  performance of the Shared Satellite or
any part  thereof  in  connection  therewith,  whether  express  or  implied  by
contract, tort, statute or other legal theory. None of TMI, its partners and the
respective  Affiliates  of TMI and  such  partners  shall  assume  or  have  any
liability  whatsoever  to AMSC  with  respect  to the grant or  exercise  of the
Temporary  Testing  Right to or by AMSC or the  performance,  nonperformance  or
improper  performance of the Shared  Satellite or any part thereof in connection
therewith.


                                    ARTICLE 5
                                CERTAIN COVENANTS

     Section  5.1.  Conduct  of  Business.  Subject to the  parties'  respective
obligations  under this  Agreement,  each of the parties shall have the right to
conduct its business in whatever  manner it deems  appropriate  and such conduct
shall not require notice to or the consent of the other party hereto.

     Section 5.2. Satellite  Capacity  Agreement and Joint Operating  Agreement.
(1) The Satellite Capacity Agreement shall,  effective as of the date hereof, be
deemed  amended as set forth in  Schedule  5.2(1),  and the  Satellite  Capacity
Agreement,  as so amended,  shall be and remain operative and enforceable by the
parties  thereto  from the date  hereof  until the date (if any) such  Satellite
Capacity  Agreement  (as so  amended)  is deemed  suspended  pursuant to Section
4.4(2) or is  terminated  pursuant to its terms,  provided that if the Satellite
Capacity  Agreement ceases to be suspended as provided in Section 4.4(2) and has
not been  terminated,  it shall once again be operative and  enforceable  by the
parties thereto.

     (2) To the extent that (i) any provision of the joint  operating  agreement
dated as of April 25, 1990 between AMSC and Telesat  Mobile Inc. (as assigned to
TMI) (as the same has been  amended  from  time to time,  the  "Joint  Operating
Agreement")  is  inconsistent  with  any  provision(s)  of this  Agreement,  the
provisions of this Agreement shall override the  inconsistent  provisions of the
Joint  Operating  Agreement,  and (ii) any provision of the  Satellite  Capacity
Agreement (as so amended),  for so long as the Satellite Capacity Agreement,  as
so  amended,  remains  operative  and  is  not  then  deemed  suspended,  all as
contemplated in Sections 4.4(2) and 5.2(1),  is inconsistent  with any provision
of  this  Agreement,   the  provision  of  this  Agreement  shall  override  the
inconsistent provision of the Satellite Capacity Agreement (as so amended).

     Section 5.3.  Reasonable  Efforts.  Subject to the terms and  conditions of
this Agreement, each of TMI and AMSC will use all reasonable efforts to take, or
cause to be  taken,  all  actions  and to do,  or cause to be done,  all  things
necessary under  applicable laws and regulations to consummate the  transactions
contemplated hereby as promptly as practicable.

     Section  5.4.  Confidentiality;  Press  Releases.  (1) Each of TMI and AMSC
will, and will use its reasonable efforts to cause its respective Affiliates and
its and their respective officers, directors,  employees, partners, accountants,
counsel, consultants,  advisors' agents and financing parties (collectively, the
"Agents")  to hold in  confidence,  unless  compelled to disclose by judicial or
administrative  process  or by  other  requirements  of  law,  all  confidential
documents and information (the "Confidential  Information") that is furnished to
such party or its Agents in connection  with this Agreement or the  transactions
contemplated  hereby and will use such information solely in connection with the
transactions contemplated hereby. To the extent that existing confidentiality or
nondisclosure  obligations  contained  in any  agreements  between  the  parties
("Existing  Obligations") prohibit the disclosure of Confidential Information to
Affiliates  or  consultants,  this  Section  5.4  shall  override  the  Existing
Obligations.  "Confidential  Information"  shall not include,  and neither party
shall have any  obligation  with  respect  to,  information  (i) that has become
public  from a source  other  than such  party or its  Agents,  or (ii) that has
become  available to such party on a  non-confidential  basis from a source that
such   party  has  no  reason  to  believe   to  be  under  an   obligation   of
confidentiality.

     (2) Except as may be required by  applicable  law or any listing  agreement
with any national  securities  exchange or quotation system,  neither party will
issue any press release or public  statement  with respect to this  Agreement or
the  transactions  contemplated  hereby  without  the consent of the other party
hereto;  provided  that the  parties  agree that,  as  promptly  as  practicable
following  the  execution of this  Agreement,  they shall issue a press  release
substantially in the form of the draft set forth on Schedule 5.4.

     Section 5.5. Access to  Information.  Subject to Section 5.4, from the date
hereof until the Traffic Transfer Date, each party will give the other party and
its  authorized  representatives  access to all technical and operating data and
information regarding the Shared Satellite to the extent necessary (i) to enable
the other party to verify the accuracy of the  representations and warranties of
such party  contained in this  Agreement and the Schedules  hereto,  and (ii) to
permit such other party to comply with its obligations hereunder.

     Section 5.6. FCC Applications.  The initial applications to be made by AMSC
to the U.S. Federal  Communications  Commission in connection with obtaining its
consent to relocate the Shared  Satellite to the Relocated  Orbital Position and
to permit the co-ownership  and operation of the Shared  Satellite  contemplated
under  this  Agreement,  and  all  documents  and  other  information  filed  in
connection  with or referred  to in such  application,  will make no  reference,
directly or indirectly,  to either party's  present markets or present or future
rights to access markets in the United States of America, Canada or elsewhere or
to provide services directly to Persons located in the United States of America,
Canada or  elsewhere.  Each of TMI and AMSC in response to comments,  replies or
submissions  by the U.S.  Federal  Communications  Commission,  or by any  other
Person in  connection  with such  application,  may  present  evidence  and make
arguments and other statements as to market access rights and other  competition
issues to challenge or counter such comments, replies or submissions. Each party
shall,  at least two Business Days prior to the filing  thereof (or such shorter
period as the circumstances may require), furnish the other party with a copy of
each  document  that it  intends  to file with the U.S.  Federal  Communications
Commission in connection with the applications,  filings, submissions, comments,
responses and replies referred to in this Section.

     Section 5.7.  Notices of Certain  Events.  Each party shall promptly notify
the other party of:

(a) any notice or other  communication from any Person alleging that the consent
of such Person is or may be required in connection with any of the  transactions
contemplated by this Agreement;

(b)  any notice or other communication from any governmental or regulatory
agency or authority in connection with any of the  transactions  contemplated by
this  Agreement  or from any  other  Person  in  connection  with  consents  and
approvals  required  from any  governmental  or  regulatory  agency or authority
hereunder  or any  submissions,  applications,  reports  or other  filings  made
thereto; and

(c) any actions,  suits, claims,  investigations or proceedings commenced or, to
its knowledge,  threatened  against it that relate to the consummation of any of
the transactions contemplated by this Agreement.

     Section 5.8. Limitation on Liability to Customers,  Resellers, etc. Each of
TMI and AMSC (in this Section,  the  "Contracting  Party") hereby  covenants and
agrees  that,  where and to the extent that such a  provision  is  permitted  by
applicable law and regulation, the Contracting Party shall in good faith seek to
specifically and expressly provide in each and every of its respective contracts
and agreements entered into after the date of this Agreement with its customers,
resellers, or other vendors of its services, and governmental entities obtaining
such services from such party, a limitation on liability of the other party,  in
substantially the following form:

                  "[the other  party (TMI or AMSC,  as the case may be)] and its
                  officers,  directors,   employees,   shareholders,   partners,
                  subcontractors,  investors or agents shall not be liable,  for
                  any reason  whatsoever,  whether in  contract or tort or under
                  any other theory of law, for losses, damages, costs, expenses,
                  liabilities  or claims  arising  out of an act or  omission of
                  [the  Contracting  Party (TMI or AMSC, as the case may be)] or
                  resulting  from the use of services  hereunder,  including but
                  not limited to any fault in a channel which results in failure
                  to  establish  service,   delays,   in-service   interruption,
                  degradation or loss or distortion of services."


                                    ARTICLE 6
                         REPRESENTATIONS AND WARRANTIES

     Section 6.1.  Representations  and  Warranties of TMI. TMI  represents  and
warrants to AMSC that:

(a) Organization and Existence.  TMI is a limited partnership duly organized and
validly  existing under the laws of the Province of Quebec,  TMI  Communications
Inc. is the general partner of TMI and is a corporation duly organized,  validly
existing and in good  standing  under the laws of Canada and TMI  Communications
Inc. has all corporate  and  partnership  power  required to execute and deliver
this Agreement in the name and on behalf of TMI and to cause the  performance by
TMI of its obligations contemplated hereunder.

(b) Corporate  Authorization.  The  execution,  delivery and  performance by TMI
Communications  Inc., in the name and on behalf of TMI, of this  Agreement  have
been  duly  approved  by all  necessary  corporate  action  on the  part  of TMI
Communications  Inc., the general  partner of TMI. This Agreement  constitutes a
valid and binding agreement of TMI.

(c) Shared Satellite Condition. To the knowledge of TMI, the description of
the  condition of the Shared  Satellite  contained in (i) the document  entitled
"Joint Technical Assessment of MSAT and AMSC-1" dated January 31, 1997, and (ii)
the documents  described in Schedule 6.1(c), is accurate.  With the exception of
the report set out as item #5 on  Schedule  6.1(c),  TMI has  furnished  to AMSC
exact  duplicates of any and all technical  reports  furnished as of the date of
this Agreement to the insurance  companies who provided  insurance  coverage for
the Shared Satellite.

(d) Governmental Authorization. The execution and delivery by TMI Communications
Inc., in the name and on behalf of TMI, of this Agreement  requires no action by
or in respect of, or filing  with,  any  governmental  body,  agency or official
other than  actions or  filings  the  failure of which to occur have not had and
would not reasonably be expected to have,  individually  or in the aggregate,  a
material adverse effect on TMI or the operation of the Shared Satellite.

(e) Non-Contravention. The execution and delivery by TMI Communications Inc., in
the name and on behalf of TMI, of this  Agreement,  and the  performance of this
Agreement by TMI Communications  Inc. on behalf of TMI, on and after the Traffic
Transfer Date, do not and will not (i) violate the partnership agreement of TMI,
(ii) violate any law, rule, regulation,  judgment,  injunction,  order or decree
applicable to TMI or any of its assets or properties,  (iii) to the knowledge of
TMI on the date of this Agreement, after due inquiry, require any consent of any
Person other than (x) consents which have been obtained on or before the date of
this  Agreement,  copies of which have been  provided to AMSC on or prior to the
date of this Agreement,  (y) Industry Canada under the Bulk Capacity Lease dated
September  14, 1988,  as amended,  Industry  Canada with respect to spectrum and
change in orbital slot, and the Communications  Security Establishment (Canada),
and (z) consents or  violations  which have not had and would not  reasonably be
expected to have, individually or in the aggregate, a material adverse effect on
TMI, or (iv) on and after the Traffic Transfer Date,  require the consent of any
Person other than (A) consents which have been obtained on or before the Traffic
Transfer  Date,  copies of which have been  provided  to AMSC on or before  such
date, and (B) consents or violations specified in Section 6.1(e)(iii)(z).

(f) Title to Shared Satellite.  TMI holds title to the Shared Satellite free and
clear of any Liens,  other than those Liens  identified in Schedule 6.1(f) ("TMI
Existing Liens") and Permitted Liens.  Effective upon the Traffic Transfer Date,
AMSC will  acquire  good and  marketable  title to the 50%  undivided  ownership
interest in the Shared Satellite, free and clear of all Liens except (x) for and
subject to the TMI Purchase  Money  Security  Interest and (y) those  granted by
AMSC to any Person other than TMI.

(g) Telesat  Agreement.  TMI has furnished to AMSC an accurate and complete copy
of the Telesat Agreement as in effect on the date of this Agreement.

(h)  Satellite  Performance.  There is no  information  (whether  in the form of
facts,  representations or opinions)  ("Information")  contained in any material
provided by TMI or Telesat to TMI's  insurers in  connection  with its insurance
claim and  settlement  with respect to its  mountain  beam (the  "Mountain  Beam
Settlement") that indicates or suggests that the coverage, health, insurability,
estimated life,  capacity or other performance  criteria of the Shared Satellite
(collectively,  the "Satellite  Performance") would be different in any material
respect from that indicated in the reports referred to in Schedule 6.1(c).

(i) Operating  Restriction.  There is no Information contained in or relating to
the Mountain Beam  Settlement  which would impose a present or future  operating
restriction  (including  the shutting down of the mountain beam) with respect to
the Shared  Satellite or that would  indicate that  insurance  coverage would be
limited in any material respect or unavailable on commercially  reasonable terms
unless such operating  restriction were imposed,  other than as described in the
reports referred to in Schedule 6.1(c).

(j)  Other  Information.  TMI is not (i)  aware of any  other  Information  with
respect  to  the  Shared  Satellite  that  would  indicate  that  the  Satellite
Performance  would be different in any material  respect from that  indicated in
the reports  referred to in Schedule 6.1(c) or (ii) in possession,  or aware, of
any non-technical  report prepared with respect to the Satellite  Performance of
the Shared  Satellite which would provide  information with respect to Satellite
Performance  different  than,  or in addition to, in any material  respect,  the
information indicated in the reports referred to in Schedule 6.1(c).

(k) Compliance with Laws. The Shared Satellite, and the operation thereof are in
compliance in all material  respects with all applicable  laws of any applicable
jurisdiction  and TMI has not received any written  notice of any alleged breach
of any such laws.

(l) Options, Rights of Purchase, etc. No Person other than AMSC has any right to
purchase the Shared  Satellite,  and, as of the Traffic Transfer Date, no Person
other than TMI and TMI's customers has any right to use, and TMI has not granted
any Person (other than its customers) any right to use, any of AMSC's  Interest.
TMI has not granted  any option or right of first  refusal  with  respect to the
Shared  Satellite other than to AMSC pursuant to this Agreement or the Satellite
Capacity Agreement.

(m) Tax  Residency.  TMI is not a  non-resident  of Canada for  purposes  of the
Income Tax Act (Canada).

     Section 6.2.  Representations  and Warranties of AMSC.  AMSC represents and
warrants to TMI that:

(a) Corporate  Existence and Power. AMSC is a corporation  dually  incorporated,
validly  existing and in good standing  under the laws of the States of Delaware
and Virginia,  respectively,  and AMSC Parent Corp. is the sole  shareholder  of
AMSC and is a corporation  incorporated,  validly  existing and in good standing
under the laws of the State of Delaware.  Each of AMSC and AMSC Parent Corp. has
all corporate  power to execute and deliver this  Agreement  and, in the case of
AMSC,  the  Security  Agreement  and to  perform  its  obligations  contemplated
hereunder and thereunder.

(b) Corporate Authorization.  The execution, delivery and performance by each of
AMSC and AMSC Parent  Corp.  of this  Agreement  and,  in the case of AMSC,  the
Security  Agreement are within their  respective  corporate powers and have been
duly authorized by all necessary  corporate  action on the part of AMSC and AMSC
Parent Corp.  This  Agreement and the Security  Agreement  constitute  valid and
binding  agreements of AMSC and this  Agreement  constitutes a valid and binding
agreement of AMSC Parent Corp.

(c)  Governmental  Authorization.  The execution and delivery by AMSC of each of
this  Agreement  and the Security  Agreement  and by AMSC Parent  Corp.  of this
Agreement  requires  no  action  by  or in  respect  of,  or  filing  with,  any
governmental  body,  agency or official other than (i) the U. S.  Securities and
Exchange  Commission as may be required in accordance with the provisions of the
U.S.  Securities  Exchange  Act of  1934,  as  amended,  and  the  U.S.  Federal
Communications   Commission  as  may  be  required  to  provide  notice  of  the
contemplated  transactions  and (ii)  actions or filings the failure of which to
occur have not had and would not reasonably be expected to have, individually or
in the aggregate, a material adverse effect on AMSC or AMSC Parent Corp.

(d)  Non-contravention.  The  execution  and  delivery  by  AMSC of each of this
Agreement and the Security  Agreement,  and the  performance  by AMSC of each of
this  Agreement  and the Security  Agreement  on and after the Traffic  Transfer
Date,  and the execution and delivery of this Agreement by AMSC Parent Corp. and
the performance by AMSC Parent Corp. of its  obligations  hereunder on and after
the  Traffic  Transfer  Date,  in each case do not and will not (i)  violate the
certificate  of  incorporation  or bylaws  of AMSC or AMSC  Parent  Corp.,  (ii)
violate  any law,  rule,  regulation,  judgment,  injunction,  order  or  decree
applicable  to AMSC or AMSC  Parent  Corp.  or any of its assets or  properties,
(iii) to the knowledge of AMSC on the date of this Agreement, after due inquiry,
require  the  consent of any  Person  other  than (x)  consents  which have been
obtained  on or prior to the date of this  Agreement,  copies of which have been
provided to TMI on or prior to the date of this Agreement,  (y) the U.S. Federal
Communications Commission, and (z) consents or violations which have not had and
would not reasonably be expected to have,  individually  or in the aggregate,  a
material  adverse  effect on AMSC or AMSC Parent Corp,  or (iv) on and after the
Traffic Transfer Date, require the consent of any Person other than (A) consents
which have been  obtained on or prior to the Traffic  Transfer  Date,  copies of
which have been  provided  to TMI on or before  such date,  and (B)  consents or
violations specified in Section 6.2(d)(iii)(z).

     Section 6.3.  Disclaimer of Warranties.  AMSC  acknowledges and agrees that
except  for the  representations  and  warranties  of TMI set  forth in  Section
6.1(c),  (f), (h), (i), (j), (k) and (l), the Shared Satellite will be purchased
on an "as is" basis.  ACCORDINGLY,  EACH PARTY COVENANTS AND AGREES THAT ANY AND
ALL  EXPRESS OR IMPLIED  WARRANTIES  OR  CONDITIONS  WITH  RESPECT TO THE SHARED
SATELLITE  OR  ANY  PART  THEREOF,  ITS  CONDITION,   DURABILITY,   PERFORMANCE,
RELIABILITY,  EXPECTED  LIFE OR  SUITABILITY  FOR ANY  PARTICULAR  USE INCLUDING
WARRANTIES OR CONDITIONS OF  MERCHANTABILITY  OR FITNESS FOR ANY PURPOSE OR USE,
WHETHER EXPRESSED OR IMPLIED BY CONTRACT,  TORT (INCLUDING NEGLIGENCE AND STRICT
LIABILITY) STATUTE OR OTHER LEGAL THEORY, ARE EXPRESSLY EXCLUDED AND DISCLAIMED.

     Section 6.4.  Disclosure.  During the period commencing on the date of this
Agreement and ending on the Traffic  Transfer  Date,  each party shall  promptly
notify the other party upon becoming aware of any  representation or warranty of
such party contained in this Agreement  becoming  untrue or incorrect.  Any such
representation  or  warranty  shall be deemed to be  amended as set forth in any
such  notification  provided that such  amendment  does not affect the rights or
obligations of the other party hereto in any material respect.


                                    ARTICLE 7
                              TERM AND TERMINATION

     Section 7.1.  Term.  Subject to this Article 7, the term of this  Agreement
shall commence on the date hereof and,  unless TMI and AMSC otherwise agree with
each other,  shall terminate upon the  decommissioning  of the Shared  Satellite
pursuant to Section 4.5 (the "Term").

     Section 7.2. Termination Prior to the Traffic Transfer Date. This Agreement
may be terminated prior to the Traffic Transfer Date:

(a) at any time, by mutual written agreement of TMI and AMSC; or

(b) at any time after the date which is the  earlier of (i) forty days after the
date of this Agreement;  and (ii) the Traffic  Transfer Date; by TMI if the AMSC
Satellite  Lessee  has  not  entered  into  written   agreements  with  Telesat,
substantially  on the terms contained in the draft  agreements  between the AMSC
Satellite  Lessee and  Telesat  (x) for  operational  services  for the  Elcor-1
satellite,  draft date November 12, 1997 and (y) for the supply and installation
of TT&C  equipment  and  software  in  Johannesburg,  South  Africa  and back up
facility in Chilworth,  England for the Elcor- 1 satellite,  draft date November
12, 1997; or

(c) at any time prior to the Traffic  Transfer Date, by TMI or AMSC, if there is
a material adverse change in the condition of the Shared Satellite;  and TMI and
AMSC  agree  that,  with  respect  solely  to the  Mountain  Beam of the  Shared
Satellite,  any complete or partial  failure or shutdown of the  Mountain  Beam,
shall not  constitute a material  adverse  change in the condition of the Shared
Satellite; or

(d) at any time on and after  March  15,  1998,  by AMSC,  if all  consents  and
approvals  of Industry  Canada and the U.S.  Federal  Communications  Commission
required for the  relocation of the Shared  Satellite to the  Relocated  Orbital
Position (and any other  Canadian or American  governmental  consent or approval
required for such relocation as a result of a change in applicable law after the
date of this  Agreement)  have not been  obtained  for any reason other than the
failure of AMSC to exercise all reasonable  commercial efforts in good faith (i)
to obtain all such required  consents and approvals of the American  government;
and (ii) to assist TMI to obtain all such required consents and approvals of the
Canadian government; or

(e) at any time on and after  March  15,  1998,  by AMSC,  if all  consents  and
approvals  of the  U.S.  Federal  Communications  Commission  required  for  the
relocation  of the  AMSC  Satellite  to a new  orbital  slot  over or  near  the
continent of Africa and the U.S.  Department  of Commerce with respect to export
controls  required  for such  relocation  (and any other  American  governmental
approvals  required for such relocation arising under a change in applicable law
after the date of this  Agreement)  have not been  obtained for any reason other
than the failure of AMSC to exercise all reasonable  commercial  efforts in good
faith to  obtain,  and to  assist  the AMSC  Satellite  Lessee to  obtain,  such
required consents and approvals; or

(f) at any time on and  after  April  30,  1998,  by TMI,  if all  consents  and
approvals  of the  U.S.  Federal  Communications  Commission  required  for  the
relocation of the Shared  Satellite to the Relocated  Orbital  Position (and any
other Canadian or American  governmental  consent or approval  required for such
relocation  as a result  of a change  in  applicable  law after the date of this
Agreement)  have not been  obtained for any reason other than the failure of TMI
to exercise all  reasonable  commercial  efforts in good faith (i) to obtain all
such  required  consents and approvals of the Canadian  government;  and (ii) to
assist AMSC to obtain all such  required  consents and approvals of the American
government; or

(g) at any time on and  after  April  30,  1998,  by TMI,  if all  consents  and
approvals  of the  U.S.  Federal  Communications  Commission  required  for  the
relocation  of the  AMSC  Satellite  to a new  orbital  slot  over or  near  the
continent of Africa and the U.S.  Department  of Commerce with respect to export
controls  required  for such  relocation  (and any other  American  governmental
approvals  required for such relocation arising under a change in applicable law
after the date of this Agreement) have not been obtained for any reason; or

(h) at any time prior to the Traffic Transfer Date, by TMI, if there shall occur
a Bankruptcy Event with respect to AMSC; or

(i) at any time prior to the Traffic Transfer Date, by AMSC if there shall occur
a Bankruptcy Event with respect to TMI; or

(j) at any time on and after 4:00 p.m. (Montreal time) on September 30, 1998, by
either party if the  transactions  contemplated  hereunder to occur on or before
the Traffic Transfer Date have not been consummated for any reason; or

(k) at any  time  prior  to the  Traffic  Transfer  Date,  by AMSC  if the  AMSC
Satellite Contract is terminated for any reason other than an event specified in
Section 7.2.

     Section 7.3.  Remedies of TMI Prior to TMI Security  Discharge Date. (1) If
at any time during the period commencing on the Traffic Transfer Date and ending
on the TMI Security Discharge Date:

(a) AMSC shall fail to pay when due the Minimum Satellite Purchase Price (or any
instalment  thereof)  or any TT&C Fees  within 10 days after  receipt of written
notice from TMI of late payment; or

(b) any Bankruptcy Event shall occur with respect to AMSC;

then TMI may declare the entire unpaid amount of the  Satellite  Purchase  Price
(or any part  thereof) and all  remaining  TT&C Fees and other  amounts owing by
AMSC and AMSC Parent  Corp.  hereunder  during the Term of this  Agreement to be
immediately due and payable,  without  presentment,  demand,  protest or further
notice of any kind,  all of which are  expressly  waived by AMSC and AMSC Parent
Corp.  Upon such  declaration,  TMI may  exercise  such rights and  remedies and
commence such legal action or  proceedings  as it, in its sole  discretion,  may
deem expedient,  including the commencement of enforcement proceedings under the
Security  Agreement or any other security  granted by AMSC and AMSC Parent Corp.
to TMI or any combination thereof, all without additional notice,  presentation,
demand,  protest,  notice  of  dishonour,  entering  into of  possession  of any
property or any other action,  notice of all of which AMSC and AMSC Parent Corp.
hereby  expressly  waive to the extent  permitted by  applicable  laws.  For the
purposes of calculating the accelerated  amounts owing hereunder for the Term of
this Agreement, the parties hereby acknowledge and confirm that (i) the expected
useful  life of the  Shared  Satellite  will  extend  for a  period  of 10 years
following the Traffic  Transfer Date; and (ii) in respect of Revenue  Adjustment
Amounts, the expected useful life of the AMSC Satellite will extend for a period
of 10 years following the Traffic Transfer Date and that the accelerated  amount
of the Revenue Adjustment  Amounts owing by AMSC upon any acceleration  pursuant
to this  Section  which  occurs (x) during  the first five years  following  the
Traffic Transfer Date, is U.S.$30,000,000, and (y) in any year thereafter, is an
amount  equal to  U.S.$30,000,000  less the  product of  U.S.$6,000,000  and the
number of years after the fifth year  following  the Traffic  Transfer Date that
the acceleration  event occurs.  The parties further  acknowledge and agree that
the  calculation  of  such  amounts  is  their  reasonable  pre-estimate  of the
accelerated  Revenue Adjustment Amounts owing hereunder  determined after taking
into account their expectations as to technological advances,  business risk and
satellite failure risk and does not constitute a penalty.

     (2) If, at any time after the TMI Security  Discharge Date, AMSC shall fail
to pay the TT&C Fees owing by it under this  Agreement  when due and payable and
such failure shall  continue for 10 days after written  notice thereof by TMI to
AMSC,  then in  addition  to any other  rights  and  remedies  of TMI under this
Agreement or otherwise,  AMSC shall cease to be entitled to have Representatives
on the  Services  Operating  Committee  or any  other  representation,  input or
decision-making  power in respect of Technical  and  Operating  Matters or other
decisions  or actions made or taken by the Services  Operating  Committee  until
such overdue amounts  (together with accrued interest thereon) have been paid in
full to TMI.

     (3) If at any time  following  the  occurrence  of a default  under Section
7.3(1)(a) but prior to  acceleration by TMI of amounts owing hereunder and prior
to commencement of enforcement  proceedings under the Security  Agreement,  such
default  is  remedied  by or on behalf of AMSC,  then TMI shall have no right to
accelerate pursuant to Section 7.3(1) or exercise any of its rights and remedies
under the Security Agreement, in each case, in respect of the occurrence of that
default (but such waiver shall not extend to the  recurrence  of such default or
the occurrence of any other default unless remedied as provided herein).

     Section 7.4.  Liabilities in Event of  Termination.  (1) Subject to Section
7.4(2), the termination or expiration of this Agreement will in no way limit any
obligation  or  liability  of either  party based on or arising from a breach or
default by such party with respect to any of its  representations  or warranties
contained  in  this  Agreement,  or  with  respect  to any of its  covenants  or
agreements contained in this Agreement which by their terms were to be performed
prior to the date of termination or expiration,  nor shall any such  termination
or expiration  release either party from any  liabilities  or obligations  under
Sections 5.4, 8.5 and 8.14.

     (2) Upon any  termination  of this  Agreement  pursuant to Section 7.2, the
Parties shall have no obligations  or liabilities to each other  hereunder or in
respect of the  transactions  contemplated  hereby except as otherwise  provided
under  Section 7.5.  Upon any such  termination  of this  Agreement  pursuant to
Section 7.2, the Parties shall have no further  obligations  or  liabilities  to
each other under the CMIS  Contract  which  agreement  shall  automatically  and
simultaneously terminate without penalty except with respect to any amounts then
owing to TMI as at and to the date of termination which amounts shall remain due
and payable to TMI and shall be deemed to have been earned by TMI (together with
all amounts previously paid to TMI).

     Section 7.5. Purchase Price Prepayment and Liquidated Damages. (1) Upon any
termination of this Agreement  pursuant to Section 7.2(b), TMI shall be entitled
to retain  U.S.$1,000,000 of the Purchase Price Prepayment.  AMSC and TMI hereby
acknowledge and agree that such amount is a genuine and reasonable  pre-estimate
of the  damages  suffered  by TMI in the event of such  termination,  and of the
costs and expenses  incurred by TMI in pursuing this  transaction at the request
of AMSC,  and not a penalty and that such  amount  shall  constitute  liquidated
damages and as such be TMI's sole right and remedy,  at law and in equity,  with
respect to the obligations of AMSC under this Agreement. The remaining amount of
the Purchase Price  Prepayment  shall be promptly  repaid by TMI to AMSC by wire
transfer or certified cheque in immediately available funds.

     (2) Upon any  termination of this  Agreement  pursuant to Section 7.2(h) or
7.2(k),  TMI shall be entitled to retain the entire amount of the Purchase Price
Prepayment.  AMSC and TMI hereby  acknowledge  and agree  that such  amount is a
genuine and reasonable  pre-estimate of the damages suffered by TMI in the event
of such  termination,  and of the costs and expenses incurred by TMI in pursuing
this  transaction at the request of AMSC, and not a penalty and that such amount
shall constitute  liquidated damages and as such be TMI's sole right and remedy,
at law and in  equity,  with  respect  to the  obligations  of AMSC  under  this
Agreement.

     (3) Upon any  termination of this  Agreement  pursuant to Section 7.2(f) or
(g) in circumstances where AMSC has failed to exercise all reasonable commercial
efforts in good faith to obtain,  or to assist in the obtaining of, the consents
or  approvals  referred  to in such  Section  7.2(f)  or (g),  then TMI shall be
entitled to retain the entire amount of the Purchase Price Prepayment.  AMSC and
TMI hereby  acknowledge and agree that such amount is a reasonable  pre-estimate
of the  damages  suffered  by TMI in the event of such  termination,  and of the
costs and expenses  incurred by TMI in pursuing this  transaction at the request
of AMSC,  and not a penalty and that such  amount  shall  constitute  liquidated
damages  and as such be TMI's sole right and remedy,  at law or in equity,  with
respect to the obligations of AMSC under this Agreement.

     (4) Except as otherwise provided in Section 7.5(3), upon any termination of
this  Agreement  pursuant to Section  7.2(c),  (d),  (e),  (f),  (g) or (i), the
Purchase  Price  Prepayment  shall  be  promptly  repaid  by TMI to AMSC by wire
transfer or certified cheque in immediately available funds.

     (5) Upon any  termination of this  Agreement  pursuant to Section 7.2(j) by
reason  of the  failure  of AMSC to  satisfy  or  deliver,  or  arrange  for the
satisfaction  or  delivery  of, any of the  conditions  set forth in Section 2.5
(other  than the  failure to obtain the  consents  to be  obtained  by TMI under
Section  2.5(c)),  TMI shall be  entitled  to retain  the  entire  amount of the
Purchase Price Prepayment.  AMSC and TMI hereby  acknowledge and agree that such
amount is a reasonable  pre-estimate of the damages suffered by TMI in the event
of such  termination,  and of the costs and expenses incurred by TMI in pursuing
this  transaction at the request of AMSC, and not a penalty and that such amount
shall constitute  liquidated damages and as such be TMI's sole right and remedy,
at law or in  equity,  with  respect  to the  obligations  of  AMSC  under  this
Agreement.

     (6) Upon any  termination of this  Agreement  pursuant to Section 7.2(j) by
reason  of the  failure  of TMI to  satisfy  or  deliver,  or  arrange  for  the
satisfaction  or  delivery  of, any of the  conditions  set forth in Section 2.6
(other  than the  failure to obtain the  consents  to be  obtained by AMSC under
Section  2.6(a)),  the Purchase Price Prepayment shall be promptly repaid by TMI
to AMSC by wire transfer or certified cheque in immediately available funds.

     (7) Upon any  termination of this  Agreement  pursuant to Section 7.2(d) or
(j) due to the  wilful  misconduct  or bad faith of TMI in failing to satisfy or
deliver, or arranging for the satisfaction or delivery of, any of the conditions
set forth in  Section  2.6 (other  than the  failure  to obtain  consents  to be
obtained by AMSC under Section 2.6(a)), TMI shall indemnify AMSC, subject to the
exclusion of liability in Section 6.3, from and against all losses,  damages and
costs it may have suffered or incurred,  directly or indirectly,  as a result of
the  termination of this Agreement under Section 7.2(d) or (j) due to the wilful
misconduct  or bad faith of TMI in failing to satisfy or deliver,  or  arranging
for the  satisfaction or delivery of, any of the conditions set forth in Section
2.6 (other  than the  failure to obtain  consents  to be  obtained by AMSC under
Section 2.6(a));  provided,  however that the maximum amount for which TMI shall
be liable  under this  Section  7.5(7) or otherwise  under this  Agreement  with
respect to any such termination is U.S.$5,000,000. The rights of AMSC under this
Section  7.5(7)  shall be in  addition to any  obligation  which TMI may have to
repay the  Purchase  Price  Prepayment  pursuant  to Section  7.5(1),  7.5(4) or
7.5(6).

     (8) Upon any termination of this Agreement  pursuant to Section 7.2(a), TMI
and AMSC shall agree upon the  entitlement of each of them to all or any part of
the Purchase Price Prepayment.

     (9) The provisions of Sections 4.4(2), 5.2(1), 5.4, 6.3, 7.4, 7.5, 7.7, 8.7
and 8.18 shall survive any termination pursuant to Section 7.2.

     Section 7.6. Procedure Upon Termination. In the event of the termination of
this  Agreement  by  either  Party  pursuant  to  Section  7.2,  notice  of such
termination will promptly be given by the terminating party to the other party.

     Section 7.7. Exclusion of Consequential and Punitive Damages. NEITHER PARTY
SHALL BE LIABLE  DIRECTLY OR  INDIRECTLY  TO THE OTHER PARTY OR TO ANY PERMITTED
ASSIGNEES OR SUCCESSOR OWNERS OF THE SHARED SATELLITE FOR ANY AMOUNTS (INCLUDING
ANY SUCH AMOUNTS CLAIMED BY THIRD PARTIES) REPRESENTING LOSS OF PROFITS, LOSS OF
BUSINESS, OR INDIRECT, SPECIAL, EXEMPLARY, INCIDENTAL, CONSEQUENTIAL OR PUNITIVE
DAMAGES,   WHETHER   FORESEEABLE  OR  NOT,   ARISING  FROM  THE  PERFORMANCE  OR
NONPERFORMANCE OR IMPROPER  PERFORMANCE OF THIS AGREEMENT,  THE SHARED SATELLITE
OR ANY PART THEREOF OR ANY ACTS OR OMISSIONS ASSOCIATED HEREWITH OR THEREWITH OR
RELATED TO THE USE OF ANY ITEMS OR SERVICES FURNISHED  HEREUNDER,  OR OCCASIONED
BY ANY DEFECT IN THE SHARED SATELLITE OR ANY PART THEREOF,  DELAY IN DELIVERY OF
THE SHARED  SATELLITE,  FAILURE OF THE SHARED  SATELLITE  OR ANY PART THEREOF TO
PERFORM OR ANY OTHER CAUSE  WHATSOEVER,  WHETHER THE BASIS OF THE  LIABILITY  IS
BREACH OF CONTRACT, TORT (INCLUDING NEGLIGENCE AND STRICT LIABILITY), STATUTE OR
ANY OTHER LEGAL THEORY, UNLESS SUCH ACT OR OMISSION ARISES FROM THE NON-CLAIMING
PARTY'S WILFUL MISCONDUCT.

     Section 7.8.  Option of AMSC to Put Interest to TMI. (1) At any time during
the Term of this Agreement  (whether  before or after the occurrence of an event
set  forth  in  Section  7.3(1)(a)  or  7.3(1)(b))  but not at any  time  that a
Satellite  Failure has  occurred and is  continuing,  AMSC may elect to transfer
good and  marketable  title in and to its Interest to TMI, free and clear of all
Liens,  and to pay to TMI on closing  pursuant to Section 7.8(2) the Put Payment
(as defined and calculated in accordance with Section 7.8(5)) and thereupon AMSC
shall be released by TMI from the  obligations  of AMSC to pay any amount of the
Satellite  Purchase  Price and TT&C  Fees,  in each case,  which are  payable in
respect of the period  commencing  after the date of closing of the  transfer of
AMSC's  Interest  to TMI  (whether  accelerated  due  under  Section  7.3(1)  or
otherwise). Any other amounts payable by AMSC pursuant to Section 7.8(4) and any
amounts due from AMSC to TMI (otherwise  than upon an  acceleration  pursuant to
Section 7.3(1) and except for the Satellite  Purchase Price and TT&C Fees) up to
and including the date of closing of the transfer of AMSC's Interest  (including
interest on any amount of the Put Payment  which is not paid when  otherwise due
hereunder,  without regard to any  acceleration  pursuant to Section 7.3(1)) are
not released or satisfied by the Put Payment but shall be and remain immediately
due and payable by AMSC hereunder  notwithstanding  any termination  pursuant to
Section 7.8(3).

     (2) Closing of the  transfer of AMSC's  Interest to TMI under this  Section
7.8 shall  occur on the  first  Business  Day which is 60 days  after the day on
which TMI receives  notice from AMSC (the "Put  Notice")  that it has elected to
transfer  its  Interest to TMI in  accordance  with this Section 7.8 (or on such
other day as the parties may agree).

     (3) At the closing of the transfer pursuant to this Section 7.8;

     (a) AMSC shall deliver to TMI:

     (i) a  conveyance  of  the  Interest  substantially  in  the  form  of  the
Conveyance (with necessary modifications) and;

     (ii) the Put Payment; and

     (b) TMI shall deliver to AMSC:

     (i) a release  of AMSC's  obligations  to pay any  amount of the  Satellite
Purchase Price and TT&C Fees, in each case,  which are payable in respect of the
period  commencing after the date of closing  (whether  accelerated due prior to
the date of closing under Section 7.3(1) or otherwise);

     (ii) executed  discharges and financing  change  statements,  designated as
discharges,  prepared by AMSC and  delivered to TMI for  execution in respect of
all  filings  and  registrations  made with  respect to the TMI  Purchase  Money
Security Interest; and

     (iii) a  termination  of the Security  Agreement and a release of AMSC from
all of its obligations thereunder.

     Upon  completion  of these  deliveries,  this  Agreement and all rights and
obligations of the parties hereunder shall terminate except for those rights and
obligations under Sections 4.4(2),  5.2(1),  5.4, 6.3, 7.4, 7.7, 7.8, 7.10, 8.5,
8.7, 8.14 and 8.18 and the parties  shall  execute a mutual  release of all such
terminated  obligations  in respect of the period  commencing  after the date of
closing.

     (4)  Following  receipt  by TMI of the Put  Notice,  TMI and AMSC shall use
their good faith efforts to obtain all regulatory  consents  necessary to permit
and, if so obtained,  TMI will cause, the Shared Satellite to be returned to its
original  orbital  position at 106.5o  West  longitude  (or such other  Canadian
orbital position as TMI may designate).  All expenses  associated with obtaining
such regulatory  approvals and with any such move of the Shared  Satellite shall
be borne solely by AMSC. In addition,  whenever the TMI Purchase  Money Security
Interest shall have become enforceable, all expenses, costs and charges incurred
by or on  behalf  of TMI and  referred  to in  Section  2.2(2)  of the  Security
Agreement,  shall be and remain  immediately  due and payable by AMSC under this
Agreement notwithstanding any termination pursuant to Section 7.8(3).

     (5)  The  terms  "Put  Payment"under  Section  7.8 and  "Satellite  Failure
Payment"  under Section 7.9, as the case may be, mean and shall be calculated as
follows:

     (a) the entire amount of the Satellite Purchase Price and TT&C Fees due and
unpaid  during the period  prior to the  delivery  of a Put Notice or  Satellite
Failure Notice,  as the case may be (excluding in each case,  amounts due solely
by reason of  acceleration  pursuant  to Section  7.3(1))  shall  remain due and
payable and, to the extent unpaid, be paid to TMI at closing;

     (b)  any  Revenue  Adjustment  Amount  due and  unpaid  during  the  period
commencing on the delivery of a Put Notice or a Satellite Failure Notice, as the
case may be, and ending on closing  shall  remain due and  payable  and,  to the
extent  unpaid,  be paid to TMI at closing  (excluding  any amount due solely by
reason of acceleration pursuant to Section 7.3(1));

     (c) any amount of the Minimum Satellite  Purchase Price which is due during
the period  commencing  on the  delivery of a Put Notice or a Satellite  Failure
Notice,  as the case may be, and ending on closing  shall be due and  payable to
TMI as at such due date but pro rated based on the proportion that the number of
days from such due date to the date of closing is to 90 days and,  to the extent
unpaid, shall be paid to TMI at closing;

     (d) any amount of the Minimum Satellite  Purchase Price which is due during
the period  commencing  after a closing under Section 7.9(2) shall be payable to
TMI only in the event of delivery of a Satellite  Failure Notice and then,  only
in the manner and at the times provided for in Sections 7.9(4) and 7.9(5);

     (e) any TT&C Fees due  during  the  period  less than 30 days prior to such
closing  shall be due and payable to TMI as at such due date but pro rated based
on the  proportion  that such number of days prior to closing is to 30 days and,
to the extent unpaid, shall be paid to TMI at closing; and

     (f) any TT&C Fees due more than 30 days prior to such closing  shall be due
and payable to TMI as at such due date and, to the extent unpaid,  shall be paid
to TMI at closing.

     In the event that the  closing of any  transfer  pursuant to Section 7.8 or
7.9,  as the case may be,  fails to occur by  reason  of the  failure  of TMI to
deliver the items specified in Section  7.8(3)(b) or 7.9(3)(b),  as the case may
be, in  circumstances  where AMSC has  tendered  the items  specified in Section
7.8(3)(a)  or  7.9(3)(a),  as the case may be, the  calculation  of the  amounts
payable  under  Section  7.8 or 7.9 shall be made on the basis that the  closing
occurred on the first  Business Day which is 60 days  following  delivery of the
Put Notice or Satellite Failure Notice, as the case may be, or such other day as
the parties may agree.

     Section 7.9.  Satellite  Failure.  (1) At any time that a Satellite Failure
has occurred and is  continuing,  AMSC may by notice to TMI elect not to use the
Shared  Satellite or any  capacity  thereon (the  "Satellite  Failure  Notice").
Within 30 days of receipt of the Satellite  Failure  Notice,  TMI shall elect by
notice to AMSC to either  (i)  arrange  for the  decommissioning  of the  Shared
Satellite  (to the extent  technically  possible  to do so) in  accordance  with
Section 4.5 or (ii) request AMSC to, and if so requested,  AMSC shall,  transfer
good and  marketable  title in and to AMSC's  Interest to TMI, free and clear of
all Liens. In either event, AMSC shall pay to TMI on closing pursuant to Section
7.9(2) the Satellite  Failure  Payment (as defined and  calculated in accordance
with  Section  7.8(5))  and  thereupon  AMSC shall be  released  by TMI from the
obligations of AMSC to pay any TT&C Fees and Revenue Adjustment Amounts, in each
case,  which are payable in respect of the period  commencing  after the date of
closing  pursuant to Section  7.9(2);  it being  understood  and agreed that the
portion of the Satellite  Failure  Payment  consisting of the Minimum  Satellite
Purchase  Price  which is due in  respect  of the  period  commencing  after the
closing under Section 7.9(2) shall be made by AMSC only in the manner and at the
times provided for in Sections  7.9(4) and 7.9(5).  Any amounts due from AMSC to
TMI up to and  including  the date of  closing  (other  than  TT&C  Fees and the
Revenue Adjustment Amounts but including interest on any amount of the Satellite
Failure  Payment which is not paid when otherwise due hereunder,  without regard
to any acceleration pursuant to Section 7.3(1)) are not released or satisfied by
the  Satellite  Failure  Payment  but shall be and  remain  immediately  due and
payable by AMSC hereunder  notwithstanding  any termination  pursuant to Section
7.9(3).

(2) Closing  pursuant to this Section 7.9 shall take place on the first Business
Day which is 60 days after the day on which TMI receives the  Satellite  Failure
Notice  from AMSC (or on such  other day as the  parties  may  agree).  At TMI's
request,  AMSC  will  assist  TMI in the  move of the  Shared  Satellite  to its
original  orbital  position of 106.5o  West  longitude  (or such other  Canadian
orbital position as TMI may designate).  All expenses  associated with obtaining
such regulatory approvals and with any such move of the Shared Satellite to such
orbital position shall be borne solely by TMI.

(3) At the closing pursuant to this Section 7.9;

(a) AMSC shall deliver to TMI:

          (i) the  Satellite  Failure  Payment  (other than the portion  thereof
          consisting  of the Minimum  Satellite  Purchase  Price which is due in
          respect of the  period  commencing  after the  closing  under  Section
          7.9(2)); and

          (ii) if requested by TMI, a conveyance  of the interest  substantially
          in the form of the Conveyance (with necessary modifications); and

(b) TMI shall deliver to AMSC:

          (i) a release  of  AMSC's  obligations  to pay TT&C  Fees and  Revenue
          Adjustment  Amounts  which  are  payable  in  respect  of  the  period
          commencing  after the closing  date  contemplated  by this Section and
          confirmation  that  the  portion  of  the  Satellite  Failure  Payment
          consisting of the Minimum  Satellite  Purchase Price due in respect of
          such period is payable  only in the manner and at the times  specified
          in Sections 7.9(4) and 7.9(5);

          (ii) executed  discharges and financing change statements,  designated
          as discharges,  prepared by AMSC and delivered to TMI for execution in
          respect of all filings and registrations  made with respect to the TMI
          Purchase Money Security Interest; and

          (iii) a  termination  of the Security  Agreement and a release of AMSC
          from all of its obligations thereunder.

     Upon  completion  of these  deliveries,  this  Agreement and all rights and
obligations of the parties hereunder shall terminate except for those rights and
obligations  under Sections 4.4(2),  5.2(1),  5.4, 6.3, 7.4, 7.7,  7.8(5),  7.9,
7.10, 8.5, 8.7, 8.14 and 8.18.

(4) Upon or from time to time after any  relocation of the AMSC Satellite or the
delivery of a replacement satellite owned or operated by AMSC, AMSC Parent Corp.
or any other Person controlled directly or indirectly by AMSC Parent Corp. which
provides L-Band satellite service to all or part of North America, TMI may elect
to purchase  restoral  capacity from AMSC in accordance  with the  provisions of
Schedule  4.4(3).  Any and all  amounts  owing by TMI to AMSC in respect of such
capacity  will be set off by AMSC against the portion of the  Satellite  Failure
Payment  consisting of the Minimum Satellite  Purchase Price then outstanding to
TMI (as such amount may be reduced  from time to time  pursuant to this  Section
7.9(4) and Section 7.9(5)).

(5) At any time and from time to time  following  the  closing  pursuant to this
Section 7.9 that:

(a) AMSC  receives  any  payments  under  the AMSC  Satellite  Contract  (or any
renewal,  extension,  substitution or replacement thereof), then AMSC shall pay,
and there shall become  immediately  due and payable,  to TMI an amount equal to
twelve thirty-eighths (12/38ths) of such payment;

(b) AMSC  receives  proceeds  upon any  sale or  other  disposition  of the AMSC
Satellite  then AMSC shall  pay,  and there  shall  become  immediately  due and
payable, to TMI an amount equal to one-half (1/2) of such proceeds;

in each  case,  up to the  aggregate  amount  equal to the  portion  of the
Satellite  Failure Payment  consisting of the Minimum  Satellite  Purchase Price
then  outstanding  to TMI (as  such  amount  may be  reduced  from  time to time
pursuant to Section 7.9(4) and this Section 7.9(5)).

     Section 7.10.  General  Rights and Remedies.  Subject to the  limitation of
liability  in Section 7.7 and the  exclusion of liability in Section 6.3, in the
event any  representation  or warranty of any party  contained in this Agreement
shall prove to have been  incorrect in any material  respect when made or deemed
to have been made or if any party fails to  perform,  observe or comply with any
of its covenants or agreements contained in this Agreement, the other party will
be entitled to whatever rights or remedies are available at law or in equity.


                                    ARTICLE 8
                                  MISCELLANEOUS

     Section 8.1.  Notices.  All notices,  requests and other  communications to
either  party shall be in writing  (including  telecopy or similar  writing) and
shall be given as follows:

if to TMI, to:

TMI Communications and Company,         with a copy to: TMI Communications Inc.
Limited Partnership                                     c/o BCE Inc.
c/o TMI Communications Inc.                             1000 de La Gauchetiere 
P.O. Box 9826                                           Street West
1601 Telesat Court                                      Suite 3800
Ottawa, Ontario, Canada K1G 5M2                         Montreal, Quebec, Canada
Fax: (613) 742-4124                                     H3B 4Y7
                                                        Fax:  (514) 397-7057

Attention:       President              Attention:      Senior Vice-President, 
with a copy to:  Vice President, Law;                     Law and Corporate 
                                                          Secretary 
                                        and with a copy to:     General Counsel







if to AMSC, to:
                                       
AMSC Subsidiary Corporation            with a copy to: American Mobile Satellite
10802 Parkridge Blvd.                                  Corporation
Reston, VA 20191-5416                                  10802 Parkridge Blvd.
Fax: (703) 758-6134                                    Reston, VA 20191-5416
                                                       Fax: (703) 758-6106    
Attention:  General Counsel
with a copy to: Director of Accounting;    Attention:  Chief Executive Officer;
                and



or to such  other  address  or  telecopier  number as such  party may  hereafter
specify for the purpose by notice to the other  party given in  accordance  with
this Section 8.01. All such notices,  requests and other communications shall be
deemed  received  on the date of receipt by the  recipient  thereof if  received
prior to 5 p.m.  in the place of receipt  and such day is a Business  Day in the
place of receipt.  Otherwise, any such notice, request or communication shall be
deemed not to have been received until the next  succeeding  Business Day in the
place of receipt.

     Section 8.2.  Amendments;  No Waivers.  (1) Any provision of this Agreement
may be amended or waived if, and only if, such amendment or waiver is in writing
and signed, in the case of an amendment, by each of TMI and AMSC, or in the case
of a waiver,  by TMI if the waiver is to be effective  against TMI or by AMSC if
the waiver is to be effective against AMSC.

     (2) Except as  expressly  set forth  herein,  no failure or delay by TMI or
AMSC in exercising any right,  power or privilege  hereunder  shall operate as a
waiver  thereof nor shall any single or partial  exercise  thereof  preclude any
other or further exercise  thereof or the exercise of any other right,  power or
privilege.

     Section 8.3.  Expenses.  All costs and expenses incurred in connection with
(a) the  negotiation,  execution and  performance  of this  Agreement or (b) the
transactions  contemplated  hereby,  shall be paid by the party  incurring  such
costs  and  expenses,  except  as  otherwise  expressly  set  forth  in (i) this
Agreement  or (ii) any other  agreement  executed  and  delivered by the parties
prior to, on or after the date of this  Agreement  relating to the allocation or
sharing of any such costs and expenses.

     Section 8.4.  Successors and Assigns.  (1) The provisions of this Agreement
shall be binding upon and inure to the benefit of TMI and AMSC.  This  Agreement
is for the sole benefit of TMI and AMSC and,  except as  otherwise  contemplated
herein,  nothing herein  expressed or implied shall give or be construed to give
any Person, other than TMI and AMSC, any legal or equitable rights hereunder.

     (2) No party may assign,  delegate or otherwise  transfer any of its rights
or obligations  under this Agreement or sell,  transfer or otherwise  dispose of
all or any part of its  Interest in the Shared  Satellite,  except as  expressly
provided in Section 8.4(3) or with the prior written  consent of the other party
hereto which shall not be unreasonably withheld; provided that:

     (a) AMSC hereby  acknowledges  and consents to the grant by TMI to BCE Inc.
of a security interest in all of TMI's rights under this Agreement and under the
Security  Agreement as security for the  obligations  from time to time owing by
TMI to BCE Inc.,  and AMSC hereby agrees that BCE Inc. may enforce all rights of
TMI  hereunder  and under the  Security  Agreement  upon the  security  interest
granted by TMI in favour of BCE Inc. becoming enforceable; and

     (b)  subject  to  receipt  by TMI of the  agreements  described  in Section
2.5(g), TMI hereby agrees to consent to the grant of a security interest by AMSC
of all of AMSC's rights under this  Agreement to Bank of America  National Trust
and  Savings  Association,  as common  collateral  agent (the  "AMSC  Collateral
Agent")  for Morgan  Guaranty  Trust  Company of New York and  Toronto  Dominion
(Texas)  Inc.  and the other  lenders and  guarantors  (collectively,  the "AMSC
Secured  Lenders")  from  time to time  under  the  U.S.$150  million  five-year
multi-draw  term loan facility  agreement  with AMSC dated June 28, 1996 and the
U.S.$75 million  five-year  revolving credit facility  agreement with AMSC dated
June 28, 1996, as security for the  obligations  of AMSC from time to time owing
to the AMSC Secured Lenders under such agreements and, subject to receipt of the
agreements  described in Section 2.5(g), TMI will agree that the AMSC Collateral
Agent may  enforce  all  rights of AMSC  hereunder  upon the  security  interest
granted by AMSC in favour of the AMSC Collateral Agent becoming enforceable.

     (3) Either party may,  without the consent of the other  Party,  assign its
rights and  obligations  hereunder  and sell any or all of its  Interest  in the
Shared Satellite to any Permitted Transferee provided that (i) the non-assigning
Party is given 30 days' prior written  notice of the proposed  assignment;  (ii)
the proposed assignee executes and delivers an assumption  agreement pursuant to
which the transferee assumes the obligations of the assigning party hereunder in
form and substance satisfactory to the other party acting reasonably;  and (iii)
in the case of an  assignment  by  AMSC,  the  proposed  assignee  executes  and
delivers  a  security  agreement  in favour  of TMI in the form of the  Security
Agreement  and  pursuant  to which TMI shall (x)  continue  to have a  perfected
security interest in the Collateral in each such  jurisdiction  where the nature
of such collateral or the nature of the business of the proposed  assignee makes
such  perfection  necessary  to  preserve  the rights of TMI under the  Security
Agreement  and under the security  agreement  with the assignee and (y) have the
same  rights  and be  subject  to the same  obligations  with  creditors  of the
proposed  assignee as TMI has pursuant to the Security  Agreement  with AMSC and
any intercreditor agreements entered into pursuant thereto.  Notwithstanding any
such  assignment  of this  Agreement  or of a  party's  rights  and  obligations
hereunder to any Permitted  Transferee,  the assigning party shall remain liable
hereunder  to the other party to the same extent as if such  assignment  had not
occurred  in the event that and to the extent that the  assignee  fails to fully
perform the assignor's obligations  hereunder,  and in the case of an assignment
by AMSC,  AMSC Parent Corp.  shall remain  liable  hereunder as guarantor to the
same extent as if the assignment had not occurred.

     Section  8.5.  Interest  on  Amounts  and Set  Off.  (1) Any  amount  owing
hereunder  which is not paid when due  (whether by  acceleration  or  otherwise)
shall bear interest (both before and after judgment) from the date on which such
amount is due until such amount is paid in full at a rate per annum equal to the
U.S. Base Rate in effect from time to time plus 2% calculated  daily and payable
on demand.

     (2) All  computations  of interest shall be made by taking into account the
actual number of days occurring in the period for which such interest is payable
and on the basis of a year of 365 or 366 days, as the case may be.

     (3) Except as otherwise  provided  under  Section 7.9, all payments made by
AMSC hereunder will be made without set off, counterclaim or other defense.

     Section  8.6.   Governing  Law.  This  Agreement  shall  be  construed  and
interpreted  in  accordance  with and  governed  by the laws of the  Province of
Ontario,  without  giving effect to the principles of conflicts of laws thereof,
and the federal laws of Canada applicable therein.

     Section 8.7. Dispute Resolution;  Arbitration. (1) Any dispute, controversy
or claim  arising out of,  relating  to, or in  connection  with this  Agreement
including any alleged breach of any provision of, any contested  termination of,
or any contested validity of, this Agreement (in each case, a "Dispute"),  shall
be referred by the party  asserting such Dispute by written notice  delivered to
the Chief Executive Officer of each of TMI and AMSC, who shall attempt,  in good
faith,  to  resolve  the  Dispute  within 30 days after  written  notice of such
Dispute is given to them. Such written notice shall contain a statement  setting
forth the nature of the Dispute. At the request of either TMI or AMSC, the Chief
Executive  Officers  shall meet at the same  location to discuss such Dispute in
good faith.  If the Chief  Executive  Officers are unable to reach  agreement to
resolve  the  Dispute  within the 30-day  period  after  written  notice of such
Dispute  is given to them,  the  Dispute  may be  submitted  by either  party to
arbitration in accordance with Sections 8.7(2) to (7) inclusive.

     (2) Any Dispute which cannot be resolved  pursuant to Section 8.7(1) may be
submitted by either party (the "Claimant") for final and exclusive settlement by
arbitration  administered by the American Arbitration  Association ("AAA") under
the AAA's  Commercial  Arbitration  Rules (the "AAA  Rules") and pursuant to the
Expedited  Procedures of the AAA Rules (regardless of the amount of the claim or
counterclaim  which is the subject of the Dispute) other than Section 54 of such
Expedited   Procedures   (relating  to  the  appointment  and  qualification  of
arbitrators),  and any  such  arbitration  shall  be  conducted  in the  English
language.

     (3) An  arbitration  shall be initiated by (i) the giving of written notice
by the Claimant to the other party (the "Respondent"),  within the 30-day period
immediately following the conclusion of the 30-day period referred to in Section
8.7(1), of its demand to arbitrate (an " Arbitration Demand"), which Arbitration
Demand shall contain a statement specifying (in reasonable detail) the nature of
the Dispute,  the dollar amount  involved (if any), and the remedy  sought,  and
(ii) the filing of three copies of such  Arbitration  Demand and three copies of
this Section 8.7,  together with the  appropriate  filing fee as provided in the
AAA Rules,  at any regional  office of the AAA. The Respondent  shall select the
place of the  arbitration,  which  shall be  either  (at the  Respondent's  sole
election)  Toronto  (Province  of  Ontario)  Canada,  or New York City (New York
State) United States of America,  and the Respondent shall,  within 5 days after
its receipt of the Arbitration  Demand,  deliver written notice of its selection
of the place of the arbitration to the Claimant, with a copy to the AAA.

     (4) The parties shall, within 7 days after receipt by the Respondent of the
Arbitration  Demand,  attempt to agree upon one arbitrator who shall  constitute
the arbitration panel and shall conduct the arbitration. If the parties agree on
a single  arbitrator,  they shall give written notice of such appointment,  with
the name and address of the arbitrator, to the AAA. If the parties are unable to
agree on a single  arbitrator  within such time period (including for the reason
that either or both parties desire a three-member  arbitration  panel) then each
party  shall  appoint,   within  the  next  3  days,  one  arbitrator  (each,  a
"party-appointed  arbitrator",  as such term is used in the AAA Rules) and shall
give  written  notice  of such  appointment,  with the name and  address  of the
party-appointed arbitrator, to the other party, with a copy to the AAA. Such two
party-  appointed  arbitrators  shall,  within the next 5 days,  appoint a third
"neutral"  arbitrator (as such term is used in the AAA Rules),  who shall act as
chairman of the arbitration  panel.  Such three arbitrators shall constitute the
arbitration  panel and shall conduct the arbitration,  and all decisions of such
three-member panel shall be taken by a majority of the arbitrators.

     (5) All filing fees payable to the AAA, including any filing fee in respect
of any  counterclaim  asserted  by  the  Respondent,  and  all  expenses  of the
arbitrator(s) constituting the arbitration panel, shall be shared equally by the
Claimant and Respondent.

     (6) Any  arbitral  award shall be in writing and shall be final and binding
on the parties.  The award may include (to the extent not inconsistent  with the
provisions  of  Section  8.7(5)),  an  award  of  costs,   including  reasonable
attorneys'  fees and  disbursements,  but may not  include an award of  punitive
damages. Judgment upon the award may be entered by any court having jurisdiction
thereof or having  jurisdiction  over the parties or their assets  including (i)
with  respect to TMI,  any court  located in the  Province  of Ontario or Quebec
(Canada)  and (ii) with respect to AMSC,  any court  located in the State of New
York, Virginia or Delaware (United States).

     (7) This Section 8.7 shall be construed and  interpreted in accordance with
and governed by the laws of the Province of Ontario,  without  giving  effect to
the  principles  of  conflicts of laws  thereof,  and the federal laws of Canada
applicable therein.

     Section 8.8. Counterparts;  Effectiveness.  This Agreement may be signed in
any number of  counterparts,  each of which  shall be deemed an  original.  This
Agreement  shall  become  effective  when  each  party  shall  have  received  a
counterpart hereof signed by the other party.



<PAGE>

     Section  8.9.  Severability.  If any  provision  of this  Agreement  or the
application to any Person or circumstance  shall be invalid or  unenforceable to
any  extent,  the  remainder  of  this  Agreement  and the  application  of such
provisions to other Persons or  circumstances  shall not be affected thereby and
shall be enforced to the greatest extent permitted by law.

     Section 8.10.  Cooperation and Further Assurances.  The parties hereto will
cooperate with each other, and will execute and deliver such further instruments
and do such further acts and things,  as may be required to expeditiously  carry
out the intent and purposes of this Agreement.

     Section 8.11. Entire Agreement. This Agreement, together with the Schedules
and Exhibits  hereto and all  agreements and documents to be delivered by either
or both the parties pursuant hereto,  constitutes the entire agreement among the
parties  hereto  with  respect  to  the  transactions  contemplated  under  this
Agreement or otherwise in respect of the Shared  Satellite,  and  supersedes all
other prior discussions,  negotiations,  agreements or undertakings with respect
thereto,  both  written  and oral.  The  parties  acknowledge  and agree that no
representations, warranties, instruments, promises, understandings or conditions
have been made or  relied  upon by the  parties  or any of their  Affiliates  in
connection  with the  transactions  contemplated  by this  Agreement  except  as
expressly set forth herein or in such other agreements or documents  referred to
in this Section.

     Section 8.12.  Structure.  The parties acknowledge that they intend to hold
their Interests  directly;  provided that the parties agree to explore  mutually
beneficial alternative structures for holding their respective Interests.  If an
alternative structure,  acceptable to each party in its sole discretion,  is not
agreed to by both  parties,  the  parties  agree  that  they  shall  hold  their
respective Interests directly.

     Section 8.13. No Fiduciary Duties; Other Business  Opportunities.  (1) None
of TMI, AMSC and their respective Affiliates shall have any duties, commitments,
obligations or covenants,  expressed or implied,  in respect of the transactions
contemplated  hereunder  other  than  those  expressly  set  forth  in (i)  this
Agreement  (including  the  Schedules  and Exhibits  hereto),  or (ii) the other
agreements  referred  to in Section  8.11.  Except as set forth  herein,  to the
fullest  extent  permitted  by  applicable  law,  neither  party  shall have any
fiduciary or similar duty, or any liability relating thereto, to the other party
(or any  Affiliate  of such other  party) in  connection  with the  transactions
contemplated  under  this  Agreement  or  otherwise  in  respect  of the  Shared
Satellite,  and each of TMI and  AMSC and  their  respective  Affiliates  hereby
waives any claim for breach of  fiduciary  duty  against  the other party or any
Affiliate of the other party in connection with the transactions contemplated by
this Agreement.

     (2) Without limiting Section 8.13(1) above, to the fullest extent permitted
by applicable  law, the doctrine of corporate  opportunity,  or other  analogous
doctrine,  shall not apply with respect to the transactions  contemplated  under
this Agreement or otherwise in respect of the Shared  Satellite.  In particular,
(i) nothing  herein shall limit  either  party hereto from  engaging in business
activities outside the transactions envisaged by this Agreement,  whether or not
in  competition  with the  operating  activities  of the other  party,  and (ii)
neither party shall




<PAGE>



have any  obligation  to the other with  respect to any  opportunity  to acquire
property or make investments outside the transactions  contemplated hereunder at
any time.

     (3) Nothing in this  Agreement is intended or shall be deemed to constitute
a  partnership,  agency,  franchise or joint  venture  relationship  between the
parties.  Except as otherwise expressly provided elsewhere herein, all revenues,
assets, liabilities,  personnel,  operations and other aspects of the respective
businesses of TMI and AMSC will remain separate and neither party shall have any
right to any revenues or assets of the other or any obligation in respect of the
liabilities or obligations of the other.

     Section 8.14.  Indemnification.  Subject to the  limitation of liability in
Section 7.7 and the  exclusion of liability in Section 6.3,  each of the parties
hereto (an  "Indemnitor")  hereby  indemnifies the other party,  its partners or
shareholders,  the  respective  Affiliates  of  such  other  party  and  of  the
respective  partners  or  shareholders  of such other  party and the  respective
officers,  directors,  employees  and  agents of each of the  foregoing  Persons
(each, an "Indemnitee")  against, and agrees to hold each of them harmless from,
any and  all  losses,  liabilities,  damages,  claims  and  expenses  (including
reasonable   expenses  of  investigation  and  reasonable   attorneys'  fees  in
connection with any arbitration or other  proceeding)  ("Damages"),  incurred by
any   Indemnitee   to  the   extent   such   Damages:   (i)  arise  out  of  any
misrepresentation  or breach of warranty,  covenant or  agreement  made or to be
performed by the Indemnitor pursuant to this Agreement;  or (ii) arise out of or
relate to a claim asserted  against any Indemnitee which claim relates solely to
the assets,  liabilities,  operations  or business  of the  Indemnitor,  whether
previously  owned,  incurred  or  conducted  or whether  acquired,  incurred  or
conducted  after  the date  hereof;  or  (iii)  to the  extent  not  covered  by
insurance, arise out of or relate to the gross negligent use or operation of the
Shared  Satellite by the Indemnitor;  or (iv) in the case of the indemnity given
hereunder by AMSC only,  arise out of or relate to any RF  interference  with or
other  disruption of  communications  or other  interference  between the Shared
Satellite and the GE Spacecraft.

     Section 8.15. Export Control Compliance.  The obligations  hereunder of TMI
and AMSC to  furnish  technical  information  to the  other are  subject  to any
restrictions  and limitations that may be imposed by any agency or department of
the federal government of the United States or Canada, respectively.

     Section 8.16. Regulatory Compliance. Notwithstanding any other provision of
this  Agreement to the contrary,  each of TMI and AMSC  acknowledges  and agrees
that it shall not,  without  first  obtaining  all required  prior  governmental
authorizations,  take any action that constitutes or results in an assignment or
transfer of control of any material governmental  authorization held by it which
is necessary to the operation of the Shared Satellite.

     Section 8.17.  Bulk Sales Act  (Ontario).  _)Although  neither TMI nor AMSC
accept that the Bulk Sales Act  (Ontario)  is  applicable  to the  transfer,  as
contemplated  herein,  by TMI to AMSC of a 50% undivided  interest in the Shared
Satellite:  (i) AMSC  hereby  waives  compliance  by TMI with the Bulk Sales Act
(Ontario)  to the  extent  (if any)  applicable  to such  transaction,  and (ii)
subject to the exclusion of liability in Section 6.3, TMI hereby indemnifies





<PAGE>




AMSC,  its  Affiliates  and their  respective  officers,  directors,  employees,
partners and agents against,  and agrees to hold each of them harmless from, any
and all losses, liabilities,  claims, expenses and damages (including reasonable
expenses of investigation and reasonable  attorneys' fees in connection with any
proceeding)   incurred  by  any  such   indemnified   Person  arising  from  the
applicability (if any) of the Bulk Sales Act (Ontario) and any failure by TMI to
comply with such legislation.

     Section 8.18. AMSC Parent Corp.  Joint and Several  Liability.  AMSC Parent
Corp.  hereby agrees that it is jointly and severally  liable with AMSC (and any
Permitted  Transferee of AMSC) in respect of the performance of all obligations,
monetary or otherwise,  of AMSC (and any Permitted Transferee of AMSC) contained
in this Agreement or in any of the other agreements  referred to in Section 8.11
(as this  Agreement  may be amended,  modified or  otherwise  changed and as any
provision of this Agreement may be waived in accordance  with Section 8.2, or as
any such other  agreement may be amended,  modified or otherwise  changed and as
any provision of any such other  agreement may be waived in accordance  with the
terms of such subject other agreement).  AMSC Parent Corp.  hereby  acknowledges
and agrees that any  amendment,  modification  or other change to this Agreement
(including  any  Schedule or Exhibit  hereto) or to any of the other  agreements
referred to in Sections  8.11, and any waiver of any provision of this Agreement
or of any such other agreement, which is consented to or granted by AMSC (or any
Permitted Transferee thereof) shall not require notice to or the consent of AMSC
Parent Corp., shall nonetheless be effective against AMSC Parent Corp. and shall
not affect the  validity or  enforceability  of the  undertaking  by AMSC Parent
Corp. contained in this



<PAGE>


Section  8.18.  The  undertaking  of AMSC Parent  Corp.  contained  in this
Section 8.18 shall be in addition to and not in substitution  for the rights and
remedies  of TMI  pursuant  to  this  Agreement  or the  Security  Agreement  or
elsewhere.

                  IN WITNESS  WHEREOF,  the  parties  hereto  have  caused  this
Agreement to be duly executed by their respective  authorized officers,  in each
case as of the day and year first above written.

                             TMI COMMUNICATIONS AND COMPANY, LIMITED PARTNERSHIP

                             By:       TMI COMMUNICATIONS INC.,
                                       its General Partner

                             By:       /s/LARRY J. BOISVERT
                             Name:     Larry J. Boisvert
                             Title:    President and Chief Operating Officer


                             By:       /s/TED IGNACY
                             Name:     Ted Ignacy
                             Title:    Chief Financial Officer


                             AMSC SUBSIDIARY CORPORATION

                             By:       /s/GARY M. PARSONS
                             Name:     Gary M. Parsons
                             Title:    Chief Executive Officer and President


                             Solely for purposes of Section 8.18:

                             AMERICAN MOBILE SATELLITE
                             CORPORATION

                             By:       /s/GARY M. PARSONS
                             Name:     Gary M. Parsons
                             Title:    Chief Executive Officer and President



<PAGE>









                              PERMITTED TRANSFEREES


A.       The "Permitted Transferees" of TMI are:

          1.   Telesat Canada or any direct or indirect wholly owned  subsidiary
               or Affiliate of Telesat Canada for so long as such  subsidiary is
               so owned or such Person remains an Affiliate.

         2.    BCE Inc. or any direct or indirect  wholly  owned  subsidiary  or
               Affiliate of BCE Inc. for so long as such  subsidiary is so owned
               or such Person remains an Affiliate.

         3.    Any Person that  succeeds to the  business  carried on by TMI and
               that is a direct or indirect wholly owned subsidiary or Affiliate
               of BCE Inc.  for so long as such  subsidiary  is so owned or such
               Person remains an Affiliate.

         4.    Any  Person(s)  which  (i)  is a  lender  to TMI  (or  any of its
               subsidiaries) or a guarantor of any obligations of TMI (or any of
               its subsidiaries);  and (ii) holds a Lien on or in respect of all
               or any part of TMI's  Interest,  or all or any part of the  other
               assets and properties of, and/or partnership interests in, TMI .


B.       The "Permitted Transferees" of AMSC are:

         1.    Any direct or indirect  wholly owned  subsidiary  or Affiliate of
               AMSC for so long as such  subsidiary  is so owned or such  Person
               remains an Affiliate.

         2.    AMSC  Parent  Corp.  or  any  direct  or  indirect  wholly  owned
               subsidiary or Affiliate of AMSC Parent Corp.  for so long as such
               subsidiary is so owned or such Person remains an Affiliate.

         3.    Any Person that  succeeds to the business  carried on by AMSC and
               that is a direct or indirect wholly owned subsidiary or Affiliate
               of AMSC Parent Corp.  for so long as such  subsidiary is so owned
               or such Person remains an Affiliate.

         4.    Any  Person(s)  which  (i) is a  lender  to  AMSC  (or any of its
               subsidiaries)  or a guarantor of any  obligations of AMSC (or any
               of its  subsidiaries);  and (ii) holds a Lien on or in respect of
               all or any  part of  AMSC's  Interest,  or all or any part of the
               other assets and properties of, and/or capital stock of, AMSC.



<PAGE>

                                                                 SCHEDULE 3.2(1)
                        TECHNICAL AND OPERATING MATTERS


I.       Technical and Operating Matters

(a)      Traffic Planning

Traffic planning issues that could potentially  affect the operation and the use
of either  party's  50% power  within the Shared  Satellite.  The process is not
intended to limit the flexibility of either party but is intended to ensure that
the operations of TMI and AMSC within the Shared Satellite are harmonized.

(b)      Access Engineering

To ensure  integrity and safe operation of the Shared  Satellite (safe access to
the Shared Satellite),  Existing Access Agreement Documents developed by each of
TMI and AMSC to control  its  existing  or future  independent  uplinks  will be
harmonized and used for this purpose.

Each party  agrees that it will mute RF  transmissions  to the Shared  Satellite
from its Communications Ground Segment (either the operational or test facility)
under any one of the following conditions:

         (i)      addition of new beams to the system; or

         (ii)     increase in beam group power limits.


(c)      Interference Troubleshooting

Intra and inter-system interference caused by the operation of the other party=s
independent  communications  ground system,  other uplinks,  or other  satellite
systems will be jointly resolved.

(d)      Satellite Reconfiguration

Hardware reconfigurations mandated by traffic considerations (either prompted by
new frequency  coordination  agreements or interference events).  Also, hardware
reconfigurations  mandated by in-orbit failure not  specifically  covered by the
Telesat Procedures.

(e)      Satellite Health Considerations

Decisions  mandated  by  observed  in-orbit  events not  covered  by  On-Station
Operation Procedures (either on the Shared Satellite or other operating HS 601s)
which could affect communications payload operation,  satellite stability and/or
pointing, expected fuel life or hardware redundancy considerations.

(f)      Determination of Power Capacity and Usage

Any  changes  to  the  power  capacity  determination,  or  to  the  operational
procedures to manage usage to be defined by the Services Operating Committee, as
provided in Schedule 4.01(a).

II.      Principles for Managing and Directing Technical and Operating Matters

In  managing  and  directing  Technical  and  Operating  Matters,  the  Services
Operating Committee shall have regard to all of the following principles, in the
following order of priority:

(a)     Satellite health shall be safeguarded.

(b)     Regulatory approvals and privileges shall be maintained and facilitated.

(c)     Adverse impacts upon the customers of either party shall be minimized.

(d)     The usage of the Shared Satellite shall be maximized.

(e)     Issues  brought  before  the  Services  Operating  Committee  shall be
        resolved as quickly as possible.



<PAGE>
                                                                SCHEDULE 3.2(2)



                                                TELESAT PROCEDURES


Attached  hereto is the table of  contents  of the  documents  constituting  the
Telesat  Procedures,  full copies of which have previously been provided to each
of TMI and AMSC.



<PAGE>
                               MSAT PROCEDURE/ROP

                                TABLE OF CONTENTS

- -------------------------------------------------------------------------------

<TABLE>
<CAPTION>

<C>          <C>                                              <C>             <C>              <C>
                                                              ROP             ISSUE            REV

TELEMETRY AND COMMAND SUBSYSTEM

9.1.0        Telesat MSAT Command System

9.1.1        Not Assigned

9.1.2        SCP Commanding                                   1.1.2           DRAFT

9.1.3        Not Assigned

9.1.4        Command File Commanding                                          DRAFT

9.1.5        MSAT Decrypt Mode Change                         1.1.4           DRAFT

             Section 4.1. -    Switch CDU 1 from Bypass Mode to Secure Mode
             Section 4.2  -    Switch CDU 2 from Bypass Mode to Secure Mode
             Section 4.3  -    Switch CDU 1 from Secure Mode to Bypass Mode
             Section 4.4  -    Switch CDU 2 from Secure Mode to Bypass Mode

9.1.6        MSAT CDU VCC Change                              1.1.5           DRAFT

             Section 4.1  -    Setting VCC for CDU 1
             Section 4.2  -    Setting VCC for CDU 2

9.1.7        CDU Key Change                                   1.1.6           DRAFT

             Section 4.1  -    Setting CDU 1 Key Address
             Section 4.2  -    Setting CDU 2 Key Address

9.1.8        Command System - CDU Timer Reset                 1.1.7           DRAFT

9.1.9        COMSEC Reset                                     2.1.3           DRAFT

             Section 4.1  -    CDU 1 COMSEC Reset
             Section 4.2  -    CDU 2 COMSEC Reset

9.1.10       CDU Control - Key Management

9.1.11       Not Assigned

9.1.12       MSAT Edmonton Command Test

9.1.13       Omni T&C Emergency Switching                     2.1.2           DRAFT

             Section 4.1  -    Emergency Switch from Dish to Omni Command and Telemetry
             Section 4.2  -    Response to SCP Fault Protection Test S3 Activation

9.1.14       Omni T&C Planned Switching                       2.1.2           DRAFT

             Section 4.1  -    Planned Switch from Dish to Omni Command
             Section 4.2  -    Planned Switch from Omni to Dish Command
             Section 4.3  -    Planned Switch from Dish to Omni Telemetry
             Section 4.4   -    Planned Switch from Omni to Dish Telemetry


TELEMETRY SUBSYSTEM PROCEDURES

9.1.15       PCM - Telesat System General

9.1.16       Not Assigned

9.1.17       Telemetry Encoder Unit (TEU) Functions           1.2.2               1                 0

             Section 4.1  -    Dwell Channel Setup
             Section 4.2  -    PCM Mode Change to Dwell
             Section 4.3  -    PCM Normal Mode Selection
             Section 4.4  -    TEU Format Selection
             Section 4.5  -    TEU Data Rate Selection

9.1.18       Not Assigned
9.1.19       Not Assigned

9.1.20       MRO Telemetry Data - Normal                      1.2.5               1                 0

9.1.21       MRO Telemetry Data - Dwell                       1.2.6           DRAFT

9.1.22       TEU Switching                                    1.2.7               1                 0

9.1.23       PCM Dwell Data Collection

9.1.24       Not Assigned
9.1.25       Not Assigned
9.1.26       Not Assigned

9.1.27       ULPC Control                                                         1                 1

9.1.28       Not Assigned
9.1.29       Not Assigned

POWER SUBSYSTEM PROCEDURES

9.1.30       Not Assigned
9.1.31       Not Assigned

9.1.32       SCP Controlled Battery Management                1.5.1           DRAFT

9.1.33       Ground Controlled Battery Management             2.5.2

9.1.34       Battery Pressure Limit Calibration               1.5.2           DRAFT

             Section 4.1  -    Manual Pressure Bias Recalibration
             Section 4.2  -    Manual SCP Pressure Correction Factor Upload
             Section 4.3  -    MPM Pressure Bias Recalibration
             Section 4.4  -    MPM SCP Pressure Correction Factor Upload

9.1.35       Not Assigned

9.1.36       Eclipse Operations Activities                    1.5.0               1                 0
                                                              1.5.1
                                                              1.5.3
             Section 4.1  -    Eclipse Monitoring Setup - First Eclipse Minus 7 Days
             Section 4.2  -    Eclipse Monitoring Setup - First Eclipse Minus 1 Day
             Section 4.3  -    Eclipse Activities
             Section 4.4  -    Post-Eclipse Activities - End of Eclipse Minus 1 Day
             Section 4.5  -    Modifying the Thermal Shock Eclipse Sequencing Parameters
             Section 4.6  -    Modifying the Thermal Shock Feedforward Parameters

9.1.37       Solstice Operations

9.1.38       Not Assigned
9.1.39       Not Assigned
9.1.40       Not Assigned
9.1.41       Not Assigned
9.1.42       Not Assigned
9.1.43       Not Assigned
9.1.44       Not Assigned
9.1.45       Not Assigned
9.1.46       Not Assigned
9.1.47       Not Assigned

9.1.48       Solar Array Performance Measurement              1.8.1           DRAFT

9.1.49       Not Assigned

PROPULSION SUBSYSTEM PROCEDURES

9.1.50       Not Assigned

9.1.51       Propellant Remaining Measurement and Residual
             Propellant Management

9.1.52       Not Assigned
9.1.53       Not Assigned
9.1.54       Not Assigned

9.1.55       Latch Valve Control                              1.4.3               1                 0

             Section 4.1  -    Uploading Latch Valve Selections for Mode Programs/Sequences
             Section 4.2  -    Reprogramming Mode Program/Sequence Latch Valve Closure Commands
             Section 4.3  -    Enable or Disable Latch Valve Checking
             Section 4.4  -    Resetting Latch Valve Check Test Status Telemetry
             Section 4.5  -    Closing all Latch Valves

9.1.56       Pressure Transducer Management                   1.4.4               1                 0

9.1.57       Not Assigned
9.1.58       Not Assigned
9.1.59       Not Assigned

ATTITUDE CONTROL SUBSYSTEM PROCEDURES

9.1.60       Not Assigned
9.1.61       Not Assigned
9.1.62       Not Assigned
9.1.63       Not Assigned

9.1.64       Switch SCP 1 to SCP 2 in Normal Mode             2.7.2               1                 0

9.1.65       Switch SCP 2 to SCP 1 in Normal Mode             2.7.2               1                 0

9.1.66       Not Assigned

9.1.67       OTS and ACCL Table Upload                        2.4.2               1                 0

9.1.68       Optimized Parameter Upload                       2.7.4               1                 0

9.1.69       SCP Parameter Upload and Verification            2.7.14          DRAFT

9.1.70       SCP Clock Control                                1.7.1               1                 0

             Section 4.1  -    Pre-Clock Set Activities
             Section 4.2  -    Clock Set Activities
             Section 4.3  -    Post-Clock Set Activities

9.1.71       RAM Patch Upload and Verification                2.7.13              1                 0

             Section 4.1  -    RAM Patch Upload
             Section 4.2  -    Magnetic Torquer (MTO) RAM Patch
             Section 4.3  -    ESA RAM Patch Setup
             Section 4.4  -    Payload (PSF) RAM Patch
             Section 4.5  -    Command (CMD) RAM Patch
             Section 4.6  -    Earth Acquisition (EAC) RAM Patch

9.1.72       Not Assigned
9.1.73       Not Assigned
9.1.74       Not Assigned
9.1.75       Not Assigned

9.1.76       Magnetic Torquer Operations                      1.7.3               1                 2

             Section 4.1  -    Initial Setup
             Section 4.2  -    Preparing to Enable the Magnetic Torquer Algorithm
             Subsection 4.2.1  - Restart
             Subsection 4.2.2  - Restart with Reprogramming
             Subsection 4.2.3  - Initialization
             Section 4.3  -    Enabling Magnetic Torquer Algorithm
             Section 4.4  -    Monitoring Autonomous Commanding
             Section 4.5  -    MWP Angle Offsets
             Section 4.6  -    Magnetic Torque Estimate Improvement
             Section 4.7  -    Individual Parameter Reprogramming
             Section 4.8  -    Disabling Magnetic Torquer Algorithm

9.1.77       Not Assigned
9.1.78       Not Assigned

9.1.79       ASWA Control                                     1.7.8               1                 1

             Section 4.1  -    Initial Torque measurements
             Section 4.2 -  Calculation  of Solar Wing Drive (SWD)  Offset Angle
             Section 4.3 - Short-Term ASWA Stepping 
             Section 4.4 - Nominal Torque Measurements 
             Section 4.5 - Correction Angle Calculation 
             Section 4.6 - ASWA Correction Angle Commanding  
             Subsection 4.6.1 - Decrease the Yoke  Deployment Angle  
             Subsection  4.6.2  -  Increase  the  Yoke Deployment Angle 
             Section 4.7 -ASWA Failure Diagnostic

9.1.80       Not Assigned

9.1.81       IRU Management                                   2.7.11              1                 0

             Section 4.1  -    Change Gyro Range
             Section 4.2  -    Update Gyro Biases
             Section 4.3  -    Change Gyro Set Selection
             Section 4.4  -    Power On/Off Gyro Heaters
             Section 4.5  -    Periodic Power Up and Calibration of Gyros
             Section 4.6  -    Power Down Gyros
             Section 4.7  -    Power Up Gyros

9.1.82       OTS Stationkeeping                               1.4.1               2                 1

             Section 4.1  -    Performing and Monitoring a Stationkeeping Maneuver
             Section 4.2  -    Aborting a Stationkeeping Maneuver

9.1.83       Not Assigned

9.1.84       Body-to-Sun Angle Gain Reprogramming             1.7.10

9.1.85       Not Assigned

9.1.86       Roll/Yaw Momentum Adjust                         2.4.5           DRAFT

9.1.87       Manual Momentum Dump Maneuver                    2.4.3

9.1.88       Not Assigned

9.1.89       Pitch Momentum Adjust                            2.4.4               1                  0

9.1.90       ESA Switch in Normal Mode                        2.7.15              1                  0

9.1.91       Not Assigned

9.1.92       ESA Bias Maintenance                             1.7.5           DRAFT

             Section 4.1  - ESA Biasing to Point Spacecraft
             Section 4.2  - ESA Biasing for Long-Term Earth Pointing

9.1.93       ESA Calibration Coefficients Upload              2.7.16              1                 0

9.1.94       STESA Sun/Moon Discrimination Operations         1.7.6               1                 0

9.1.95       Not Assigned

9.1.96       SCP Fault Protection Management                  2.7.4           DRAFT

             Section 4.1  -    Hardware Toggle Enable/Disable
             Section 4.2  -    Software Toggle Enable/Disable
             Section 4.3  -    VLSI and PWDT Response Enable/Disable
             Section 4.4  -    Test Latch/Audit Trail Reset
             Section 4.5  -    Response Flag Reset
             Section 4.6  -    Stored Command Processing Disable Allow/Disallow
             Section 4.7  -    Test Enable/Disable
             Section 4.8  -    Response Enable/Disable
             Section 4.9  -    Fault Protection San Enable/Disable
             Section 4.10 -    Unit Availability Table Maintenance
             Section 4.11 -    Fault Protection Parameter Maintenance
             Section 4.12 -    Fault Protection Initialization

9.1.97       Solar Wing Drive Management                      2.7.9

9.1.98       RPM Management                                   1.7.7               1                 0

             Section 4.1  -    RPM Switch to Ground Stepping Mode
             Section 4.2  -    Manual RPM Stepping
             Section 4.3  -    RPM Step Deadband Parameter Upload
             Section 4.4  -    RPM Step Inhibit Time Parameter Upload

9.1.99       SCP Memory Latch Control                         1.7.2                1                0

THERMAL SUBSYSTEM PROCEDURES

9.1.100      Not Assigned

9.1.101      Communications Heater Control                                    1.6.1            DRAFT

             Section 4.1  -    Maintenance Communications Heaters Disable
             Section 4.2  -    Maintenance Communications Heaters Enable
             Section 4.3  -    Replacement Communications Heaters Disable
             Section 4.4  -    Replacement Communications Heaters Enable

9.1.102      Not Assigned
9.1.103      Not Assigned

CONFIGURATION TABLES

9.1.104      Not Assigned
9.1.105      Not Assigned
9.1.106      Not Assigned
9.1.107      Not Assigned
9.1.108      Not Assigned
9.1.109      Not Assigned


PAYLOAD PROCEDURES

9.1.110      Payload Operations - General

9.1.111      MSAT Local Oscillators Initial Turn-On
             Configuration                                                        1                 0

9.1.112      Reference Local Oscillator Frequency Adjust                          1                 0

9.1.113      SSPA T-Switch Initial Configuration                                  1                 0

             Section 4.1  -    North SSPA T-Switches Initial Configuration
             Section 4.2  -    South SSPA T-Switches Initial Configuration

9.1.114      SSPA Initial Turn-On                                                 1                 0

9.1.115      L-Band Upconverter Initial Configuration                             1                 0

9.1.116      L-Band Upconverter Sub-Band Filter and                               1                 0
             Attenuator Control

9.1.117      Ku-Band Receiver Initial Configuration                               1                 0

9.1.118      Not Assigned
9.1.119      Not Assigned

9.1.120      Ku-Ku Attenuator Control                                             1                 0

9.1.121      Solstice/Equinox Payload Attenuation

9.1.122      Not Assigned
9.1.123      Not Assigned

9.1.124      LTWTA Initial Configuration                                          1                 0

9.1.125      Ku-Band Upconverter Initial Configuration                            1                 0

9.1.126      L-Band Receiver Initial Configuration                                1                 0

9.1.127      L-Band Receiver Sub-Band Filter and
             Gain Control                                                         1                 0

9.1.128      LTWTA Manual Gain Control                                            1                 0

9.1.129      Not Assigned
9.1.130      Not Assigned

NON-NOMINAL OPERATIONS and TMI INTERFACE PROCEDURES

9.2.1        AMSC Traffic Restoral                                                1                 0
9.2.2        Not Assigned
9.2.3        Not Assigned
9.2.4        Not Assigned
9.2.5        Not Assigned
9.2.6        Not Assigned
9.2.7        Not Assigned
9.2.8        Not Assigned
9.2.9        Not Assigned
9.2.10       Not Assigned
9.2.11       Not Assigned
9.2.12       Not Assigned
9.2.13       Not Assigned
9.2.14       Not Assigned
9.2.15       Not Assigned
9.2.16       Not Assigned
9.2.17       Not Assigned
9.2.18       Not Assigned
9.2.19       Not Assigned

9.2.20       TMI/Telesat Communications Protocol                                  1                 1

EMERGENCY OPERATIONS - GENERAL PROCEDURES

9.3.0        Satellite Emergency Team                                             1                 2

9.3.1        Emergency Recovery Operations - General          2.0.1               1                 0

9.3.2        Not Assigned

9.3.3        Command System Failure - Diagnostic and Recovery 2.1.1               1                 0

9.3.4        Emergency - Manual Command                       2.1.1               1                 0

             Section 4.1  -    Configuration and Commanding
             Seciton 4.2  -    Pulse Command Execution
             Section 4.3  -    Non-SCP Serial Command Execution
             Section 4.4. -    SCP Serial Command Execution

9.3.5        Telemetry System Failure-Diagnostic and Recovery 2.2.1                1                0

9.3.6        Not Assigned
9.3.7        Not Assigned
9.3.8        Not Assigned
9.3.9        Not Assigned

9.3.10       Power Subsystem Failure - General                2.5.1

9.3.11       Bus Short/Bus Undervoltage Transient Recovery

9.3.12       Not Assigned
9.3.13       Not Assigned

9.3.14       Battery Charge Controller Failure

9.3.15       Battery Discharge Controller Failure

9.3.16       Not Assigned

9.3.17       Solar Wing Drive (SWD) Failure                   2.7.10

9.3.18       Solar Wing Drive (SWD) Potentiometer Failure

9.3.19       Not Assigned
9.3.20       Not Assigned
9.3.21       Not Assigned

9.3.22       Not Assigned
9.3.23       Not Assigned
9.3.24       Not Assigned

9.3.25       Attitude Control System Failure - General        2.7.1

9.3.27       MWA Unit Failure

9.3.27       MWP Unit Failure                                 2.7.7

9.3.28       Not Assigned

9.3.29       IRU Unit Failure                                 2.7.12          DRAFT

             Section 4.1  -    Emergency Response to Gyro Failure
             Section 4.2  -    Diagnosis as Operator Errors
             Section 4.3  -    Diagnosis as Spacecraft Gyro Failure

9.3.30       STESA Unit Failure                               2.7.3

9.3.31       Not Assigned
9.3.32       Not Assigned

9.3.33       Magnetic Torquer Failure                         2.7.8

9.3.34       RPM Unit Failure                                 2.7.17

9.3.35       Not Assigned

9.3.36       Attitude Recovery                                2.7.6

9.3.37       Not Assigned

9.3.38       Long-Term Sun Hold Mode                          2.7.5

9.3.39       Not Assigned
9.3.40       Not Assigned
9.3.41       Not Assigned
9.3.42       Not Assigned
9.3.43       Not Assigned

9.3.44       ULPC Failure

9.3.45       Local Oscillators - Failure Recovery                                 1                 1

9.3.46       Payload Overdrive Recovery                       2.7.20E             1                 1

             Section 4.1  -    Payload Overdrive Threshold Aadjustments
             Section 4.2  -    Payload Overdrive Response Reset
             Section 4.3  -    Payload Overdrive Response Recovery

9.3.47       L-Band Upconverter Emergency Turn Off                                1                 0

9.3.48       SSPA Failure Recovery                                                1                 5

             Section 4.1  -    SSPA Failure Recovery Procedure - General
             Section 4.2  -    SSPA 3 Failure Recovery
             Section 4.3  -    SSPA 4 Failure Recovery
             Section 4.4  -    SSPA 7 Failure Recovery
             Section 4.5  -    SSPA 8 Failure Recovery
             Section 4.6  -    SSPA 11 Failure Recovery
             Section 4.7  -    SSPA 12 Failure Recovery
             Section 4.8  -    SSPA 13 Failure Recovery
             Section 4.9  -    SSPA 14 Failure Recovery

9.3.49       L-Band Upconverter Failure Recovery                                  2                 2

             Section 4.1  -    L-Band Upconverter Failure Recover - General
             Section 4.2  -    L-Band Upconverter 1 Total Failure
             Section 4.3  -    L-Band Upconverter 2 Total Failure
             Section 4.4  -    L-Band Upconverter 3 Total Failure
             Section 4.5  -    L-Band Upconverter 4 Total Failure
             Section 4.6  -    L-Band Upconverter 5 Total Failure
             Section 4.7  -    L-Band Upconverter 6 Total Failure
             Section 4.8  -    L-Band Upconverter 1 Partial Failure
             Section 4.9  -    L-Band Upconverter 2 Partial Failure
             Section 4.10 -    L-Band Upconverter 3 Partial Failure
             Section 4.11 -    L-Band Upconverter 4 Partial Failure
             Section 4.12 -    L-Band Upconverter 5 Partial Failure
             Section 4.13 -    L-Band Upconverter 6 Partial Failure

9.3.50       Forward Repeater, Ku-Band Receiver - Failure Recovery                1                 0

9.3.51       Reverse Repeater, LTWTA - Failure Recovery

             Section 4.1  -    Ku-Band LTWTA 1 Failure Recovery
             Section 4.2  -    Ku-Band LTWTA A Failure Recovery

9.3.52       LTWTA Filament Boost                                                 1                 0

             Section 4.1  -    Ku-Band LTWTA 1 Filament Boost
             Section 4.2  -    Ku-Band LTWTA A Filament Boost
             Section 4.3  -    Ku-Band LTWTA B Filament Boost

9.3.53       Ku-Band LTWTA Timer Override                                         1                 0

             Section 4.1  -    Ku-Band LTWTA 1 Timer Override
             Section 4.2  -    Ku-Band LTWTA A Timer Override
             Section 4.3  -    Ku-Band LTWTA B Timer Override

9.3.54       Ku-Band LTWTA Trip-Off Recovery                                      1                 1

             Section 4.1  -    Ku-Band LTWTA 1 Trip-Off Recovery
             Section 4.2  -    Ku-Band LTWTA A Trip-Off Recovery
             Section 4.3  -    Ku-Band LTWTA B Trip-Off Recovery

9.3.55       Ku-Band Upconverter Failure Recovery                                 1                 0

9.3.56       L-Band Receiver - Failure Recovery                                   2                 2

             Section 4.1  -    L-Band Receiver Failure Recovery - General
             Section 4.2  -    L-Band Receiver 1 Total Failure
             Section 4.3  -    L-Band Receiver 2 Total Failure
             Section 4.4  -    L-Band Receiver 3 Total Failure
             Section 4.5  -    L-Band Receiver 4 Total Failure
             Section 4.6  -    L-Band Receiver 5 Total Failure
             Section 4.7  -    L-Band Receiver 6 Total Failure
             Section 4.8  -    L-Band Receiver 1 Partial Failure
             Section 4.9  -    L-Band Receiver 2 Partial Failure
             Section 4.10 -    L-Band Receiver 3 Partial Failure
             Section 4.11 -    L-Band Receiver 4 Partial Failure
             Section 4.12 -    L-Band Receiver 5 Partial Failure
             Section 4.13 -    L-Band Receiver 6 Partial Failure

CONSTRAINTS

9.4.0        Not Assigned

</TABLE>


                                                                 SCHEDULE 4.1(2)


             DETERMINATION OF ALLOTTED USAGE OF THE SHARED SATELLITE


I.       Determination of Power Capacity

TMI and AMSC are each  entitled to 50% of the  available  Radio  Frequency  (RF)
power in each of the North  Hybrid  Matrix  Amplifier  (HMA)  (East and  Central
Beams) and South HMA (Mountain,  West, South, Alaska/Hawaii Beams). For planning
purposes,  combined operation at 16 dB Noise Power Ratio (NPR) is adopted as the
baseline as of the commencement of the satellite  sharing,  subject to change as
approved by the Services  Operating  Committee  (pursuant to Section 3.02 of the
Agreement).  The nominal operating power for each HMA at 16 dB NPR is defined at
54.3 dBW at a gain  reference  level of 31.3 dBi  (see  below).  In-orbit  power
capability  may be more or less than  this  reference  level.  The  addition  or
reduction in performance  margin, if any and once clearly  established,  will be
shared equally by TMI and AMSC.

The 31.3 dBi gain reference  level referred to above defines the Nominal Edge of
Coverage (EOC) of the four beams (East, Central,  Mountain,  West) as defined in
spacecraft  contract  specifications  (ref.  4).  The  defined  EOC gain for the
Alaska/Hawaii  Beam is 28 dBi and the gain for the South  Beam is 26.4  dBi.  As
outlined in ref. 4, the combined AMSC and TMI traffic will not exceed 80% of the
nominal  operational power of an HMA (the nominal being defined at 16 dB NPR for
an EIRP of 54.3 dBW) in a single beam.  In such an operating  mode,  each of TMI
and AMSC has the right of access to 40% of the HMA power  within a single  beam,
with the exception of the Mountain Beam.

Unless otherwise approved by the Services Operating Committee,  the operation of
the Mountain Beam will be limited to 11% of the South HMA's maximum  operational
power,  referenced at 16 dB NPR level  (equivalent to 13% of  operational  power
referenced at the 18 dB NPR level).  Each of TMI and AMSC therefore has right of
access to 5.5% of the South HMA maximum operational power in the Mountain Beam.

If the power limit of a beam is revised in the future, each of TMI and AMSC will
be entitled to up to half of the maximum operational power of such beam.

II.      Determination of Allotted Usage

The Services Operating  Committee shall define operational  procedures to manage
usage.  This is required to establish  soft/hard alarm levels for the RAM Patch,
to control the payload drive level and to ensure safe operation of the payload.

In the absence of these  operational  procedures and for planning purposes usage
will be tracked by  existing  software  that uses the daily CGS Call  Processing
Records (CPR), in conjunction  with data  concerning  traffic not handled by the
CGS, to generate  daily power usage  profiles  for each party and for each beam.
The daily  power Busy Hour data for each beam will be  averaged  over 5 business
days to  generate a weekly  average.  The largest  weekly  average in a calendar
month will  represent the monthly usage (the "Monthly  Power  Usage").  The same
procedures  shall also be used to account  for and manage  Excess  Capacity  (as
defined in Section 4.4(1) of the Agreement).

III.     Spectrum Considerations:

It is assumed that each of the parties will use its coordinated  L-Band spectrum
in accordance with its 50% on-board power.

If Satellite  failures adversely impact the available spectrum to either or both
parties,  TMI and AMSC will cooperate to minimize the impact and seek to arrange
for an equitable burden sharing (without charge), proportional to the respective
Coordinated   Spectrum  under  the  on-going  Memorandum  of  Understanding  for
Intersystem  Coordination  of Certain  Geostationary  Mobile  Satellite  Systems
Operating in the Bands  1525-1544/1545-1559 MHz and  1626.5-1645.5/1646.5-1660.5
MHz, dated June 18, 1996.




<PAGE>


                                                                 SCHEDULE 4.4(1)



                           EXCESS CAPACITY AND PRICING


If a  party  has  requested  use  of  the  other  party's  Excess  Capacity  (as
contemplated  in Section  4.4(1) of the  Agreement),  the party  receiving  such
Excess  Capacity  shall pay to the party  allocating  such Excess  Capacity,  in
advance,  an amount equal to U.S.  $24,109 per month (or portion  thereof,  on a
pro-rated basis) during the Specified Time Period for each 0.5% of the available
Radio Frequency (RF) power in either the North or South Hybrid Matrix  Amplifier
(as referenced in Schedule 4.1(2)) included within the specified Excess Capacity
without regard to the receiving party's use or non-use of such Excess Capacity.



<PAGE>



                                                                 SCHEDULE 4.4(3)
                               RESTORAL CAPACITY

1.        In this Schedule 4.4(3):

          "Shared Satellite  Degradation" means any diminution or degradation in
          the  condition  of the Shared  Satellite  below that  specified in the
          documents  relating to the condition of the Shared Satellite listed in
          Schedule 6.1(c) of this Agreement;

          "AMSC  Satellite  Degradation"  means any diminution or degradation in
          the  condition  of the AMSC  Satellite  below  that  specified  in the
          documents  relating to the condition of the AMSC  Satellite  listed at
          the end of this Schedule 4.4(3); and

          "Restoral Capacity" means Radio Frequency (RF) power.

Restoral Capacity to TMI
- ------------------------

2. TMI shall, to the extent reasonably  possible,  mitigate any Shared Satellite
Degradation which affects it by utilizing:

(a)       its own Allotted Usage; and/or

(b)       Excess Capacity purchased by it; and/or

(c)       any  other  L-Band  Satellite  which  it or  any  Person  directly  or
          indirectly controlled by TMI owns or operates.

3. If TMI is unable to fully mitigate such Shared  Satellite  Degradation as set
out in paragraph 2 above,  then to the extent reasonably  possible,  AMSC shall,
immediately  upon its receipt of a written  request for Restoral  Capacity  from
TMI, commence to provide Restoral Capacity from its Allotted Usage and/or Excess
Capacity  purchased  by it to TMI,  at the  price of  U.S.$24,109  per month (or
portion  thereof,  on a pro-rated  basis) for each 0.5% of the  available  Radio
Frequency  (RF) power in either the North or South  Hybrid  Matrix  Amplifier so
provided (such RF power being  determined in accordance  with Schedule  4.1(2)),
provided that for the purposes of this paragraph 3, the extent to which AMSC has
Restoral Capacity  available to sell will be determined solely with reference to
actual (and not to forecasted) customer usage.

4. If TMI is unable to fully mitigate such Shared  Satellite  Degradation as set
out in either  paragraph 2 or 3 above, and if, at the time at which TMI provides
its written  request for Restoral  Capacity to AMSC,  AMSC is  providing  L-Band
satellite  service to all or any part of North America using the AMSC Satellite,
then to the extent reasonably possible, AMSC shall, immediately upon its receipt
of such written  request,  commence to provide  Restoral  Capacity to TMI on the
AMSC Satellite,  at the price of U.S.$24,109 per month (or portion thereof, on a
pro-rated  basis) for each 0.5% of the available  Radio  Frequency (RF) power in
either the North or South Hybrid Matrix Amplifier so provided. In this paragraph
4, such RF power shall be determined on the basis of a nominal  operating  power
for each HMA at 16dB NPR  defined at 54.3 dBW for the South  Matrix and 53.2 dBW
for the North  Matrix at a gain  reference  level of 31.3 dBi. The 31.3 dBi gain
reference  level  defines the Nominal Edge of Coverage of the 3 beams  (Central,
Mountain, West) as defined in the AMSC Satellite contract specifications.

5. If TMI is unable to fully mitigate such Shared  Satellite  Degradation as set
out in any of  paragraphs  2, 3 or 4 above,  and if,  at the  time at which  TMI
provides its written  request for Restoral  Capacity to AMSC,  AMSC is providing
L-Band satellite service to all or any part of North America using any satellite
which is owned or operated by either  AMSC or AMSC  Parent  Corp.  or any Person
controlled  directly or  indirectly  by AMSC Parent Corp.  other than the Shared
Satellite or the AMSC  Satellite,  then AMSC shall,  within two Business Days of
its receipt of such written request, deliver a written offer to provide Restoral
Capacity to TMI on such other satellite (the "Offer to Provide"), at a price and
on terms and conditions  specified in such Offer to Provide,  such price,  terms
and  conditions to be no less  favourable  than those given or quoted by AMSC to
any of its actual or potential  wholesale  customers as at the date of the Offer
to Provide.  TMI shall have up to 10  Business  Days from the date upon which it
receives such Offer to Provide to deliver a written  acceptance of same to AMSC,
failing with AMSC may revoke such Offer to Provide.

6.  Notwithstanding  anything  else in this Schedule  4.4(3),  AMSC shall not be
obliged to provide  Restoral  Capacity to TMI if to do so would  require AMSC to
pre-empt any of its existing customers.

Restoral Capacity to AMSC
- -------------------------

7. AMSC shall, to the extent reasonably possible,  mitigate any Shared Satellite
Degradation or AMSC Satellite Degradation which affects it by utilizing:

(a)       its own Allotted Usage; and/or

(b)       Excess Capacity purchased by it; and/or

(c)       any other L-Band Satellite which it or AMSC Parent Corp. or any Person
          directly  or  indirectly  controlled  by  AMSC  Parent  Corp.  owns or
          operates.

8. If AMSC is unable to fully mitigate such Shared Satellite Degradation or AMSC
Satellite  Degradation  as set out in  paragraph  7  above,  then to the  extent
reasonably  possible,  TMI  shall,  immediately  upon its  receipt  of a written
request for Restoral  Capacity from AMSC,  commence to provide Restoral Capacity
from its Allotted Usage and/or Excess  Capacity  purchased by it to AMSC, at the
price of U.S. $24,109 per month (or portion  thereof,  on a pro-rated basis) for
each 0.5% of the  available  Radio  Frequency  (RF) power in either the North or
South Hybrid  Matrix  Amplifier so provided  (such RF power being  determined in
accordance  with  Schedule  4.1(2)),  provided  that  for the  purposes  of this
paragraph  8, the extent to which TMI has  Restoral  Capacity  available to sell
will be determined solely with reference to actual (and not forecasted) customer
usage.

9. If AMSC is unable to fully mitigate such Shared Satellite  Degradation as set
out in any of  paragraphs  7 or 8  above,  and if,  at the  time at  which  AMSC
provides  its written  request for  Restoral  Capacity to TMI,  TMI is providing
L-Band satellite service to all or any part of North America using any satellite
which  is  owned  or  operated  by TMI  or any  Person  controlled  directly  or
indirectly by TMI other than the Shared  Satellite,  then TMI shall,  within two
Business Days of its receipt of such written request, deliver a written offer to
provide  Restoral  Capacity  to AMSC on such  other  satellite  (the  "Offer  to
Provide"),  at a price and on terms and  conditions  specified  in such Offer to
Provide,  such price,  terms and conditions to be no less  favourable than those
given or quoted by TMI to any of its actual or potential  wholesale customers as
at the date of the Offer to Provide. AMSC shall have up to 10 Business Days from
the date upon  which it  receives  such  Offer to  Provide  to deliver a written
acceptance  of same to TMI,  failing  which  the TMI may  revoke  such  Offer to
Provide.

10.  Notwithstanding  anything  else in this Schedule  4.4(3),  TMI shall not be
obliged to provide  Restoral  Capacity to AMSC if to do so would  require TMI to
pre-empt any of its existing customers.

11. AMSC shall only be entitled to request that TMI provide Restoral Capacity to
mitigate an AMSC Satellite  Degradation when AMSC is using the AMSC Satellite to
provide L-Band satellite service to all or any part of North America.


<PAGE>


<TABLE>
<CAPTION>

            DOCUMENTS RELATING TO THE CONDITION OF THE AMSC SATELLITE


<S>      <C>                                                                                 <C>
1        AMSC Satellite Status, Monthly Report, AMSC-1                                       October 1-31, 1997

2        In-Orbit Renewal Presentation                                                       August, 1996

3        AMSC-1, Material Up-date to August 1996 On-Orbit Insurance Renewal Presentation     May, 1997

4        AMSC-1 Payload In-Orbit Test Report

5        MSAT (M2) Bus In-Orbit Test Report                                                  August, 1995

6        MSAT M2 Receiver Failure Investigation, Summary Report                              March 1, 1996

7        MSAT SSPA Turn-Off Anomaly Investigation, Summary Report                            March 15, 1996

8        Report on the MS Second Investigation of the East Beam, SPAR                        March 22, 1996

9        Proof of Loss Statement, Launch Policy Claim (Binder)

         #     AMSC Report "AMSC-1 Forward  Repeater East Beam EIRP  Fluctuation
               Frequency and Magnitude", April 2, 1996

         #     AMSC  Report  "Review  of  On-Orbit  Test  Data of the East  Beam
               Forward   Repeater  of  AMSC-1  since  the  In-Orbit  Test  Phase
               Completed May 7, 1995", March 29, 1996

         #     AMSC Report  "CONUS  Coverage  Using West,  Mountain  and Central
               Beams - Achieved  Using  Antenna  Repointing  and Higher  Up-Link
               EIRP's", April 3, 1996

         #     Hughes/SPAR Report "Report on MSAT M2 Second Investigation of the
               East Beam", April 3, 1996

         #     Hughes Report  "AMSC-1 RF Gain Change Anomaly  Report",  December
               22, 1995

         #     Addendum to the hughes Report of December 22, 1995

         #     Hughes  Report  "MSAT  M2  In-Orbit  Anomalies  Summary  Report",
               January 12, 1996

         #     AMSC Report  "AMSC-1 EIRP Drop Test Results of Testing  Conducted
               Since December 22, 1995", March 5, 1996

         #     AMSC  Report  "Estimation  of AMSC-1  95%  CONUS 3 Beam  Coverage
               Following March 4, 1996 Reflector  Repositioning",  April 4, 1996
             
10       Proof of Loss Statement, On-Orbit Policy Claim

         #     AMSC Report "AMSC-1 Forward  Repeater East Beam EIRP  Fluctuation
               Frequency and Magnitude", April 2, 1996

         #     AMSC  report  "Review  of  On-Orbit  Test  Data of the East  Beam
               Forward   Repeater  of  AMSC-1  Since  the  In-Orbit  Test  Phase
               Completed May 7, 1995", March 29, 1996

         #     AMSC Report  "CONUS  Coverage  Using West,  Mountain  and Central
               Beams - Achieved  Using  Antenna  Reporting  and  Higher  Up-Link
               EIRP's", April 3, 1996

         #     Hughes/Spar Report "Report on the MSAT M2 Second Investigation of
               the East Beam", April 3, 1996

         #     Hughes/Spar  Report  "Summary  Report on MSAT M2 OHM  Anomaly and
               Recovery", September 20, 1995

         #     Hughes Report  "AMSC-1 RF Gain Change Anomaly  Report",  December
               22, 1995

         #     Addendum to the Hughes Report of December 22, 1995

         #     Hughes  Report  "MSAT  M2  In-Orbit  Anomalies  Summary  Report",
               January 12, 1996

         #     AMSC Report  "AMSC-1 EIRP Drop Test Results of Testing  Conducted
               Since December 22, 1995", March 5, 1996

         #     AMSC Report "Reston RF Terminal Testing  Conducted May 10, 1995",
               April 3, 1996

         #     AMSC  Report  "Estimation  of AMSC-1  95%  CONUS 3 Beam  Coverage
               Following March 4, 1996 Reflector  Repositioning",  April 4, 1996
           
11       Letter  from  Spar to AMSC Re:  Operating  Levels  for the M2Spacecraft             July 3, 1997

</TABLE>

<PAGE>

                                                                 SCHEDULE 5.2(1)


                    AMENDMENT TO SATELLITE CAPACITY AGREEMENT


Effective upon execution of the Agreement,  the Satellite  Capacity Agreement is
deemed  amended to provide that neither party shall have the right to invoke the
Option to Purchase set out in  paragraph 5 of the letter dated  October 18, 1993
from AMSC to TMI (which letter amended the Satellite  Capacity  Agreement),  and
that if this Agreement  terminates  prior to the Satellite  Capacity  Agreement,
then the parties shall again have the right to invoke such Option to Purchase.



<PAGE>



                                                                    SCHEDULE 5.4


                            FORM OF PRESS RELEASE(S)


Reference: 
          ------------------


FOR IMMEDIATE RELEASE

                     TMI, American Mobile Satellite team up
                  on powerful mobile communications satellite.
   Joint ownership and operation of MSAT satellite to benefit both companies.

OTTAWA, CANADA and RESTON, VIRGINIA,  December XX, 1997 C TMI Communications and
American Mobile Satellite  Corporation (Nasdaq:  SKYC) today announced that both
companies  will  use  the  powerful  MSAT-1  satellite  to  bring  their  mobile
communications services to customers.  Under an agreement signed today, American
Mobile  Satellite will buy a half interest in MSAT-1 from TMI, and the companies
will  share the costs of  satellite  operations.  The  agreement  is  subject to
regulatory approvals in both Canada and the US.

In a related  announcement  issued today by American Mobile Satellite,  the twin
MSAT-2 satellite will be leased to African Continental  Telecommunications  Ltd.
(ACTEL) and moved to provide service in southern Africa.

"In North America,  MSAT mobile satellite technology is well-suited to the needs
of maritime,  government,  transportation,  utility and oil and gas industries,"
said Gary M. Parsons,  president and chief executive  officer of American Mobile
Satellite.  "This agreement  allows  American Mobile  Satellite to develop these
targeted business  applications while moving more quickly to a second generation
solution."

Parsons' enthusiasm was echoed by Larry Boisvert,  TMI's president and CEO. "TMI
wants to use the MSAT satellite to position the company for success in the North
American mobile communications market," Boisvert said. "By working with American
Mobile Satellite, TMI will be better positioned to serve and aggressively expand
its customer base."

TMI and American Mobile  Satellite are no strangers to doing business  together.
Through a joint development and operating agreement,  they funded the design and
development  of the unique MSAT  mobile  satellite  technology.  During 1995 and
1996, TMI and American Mobile Satellite placed twin MSAT satellites into service
over Canada and the United States.

Unlike  proposed low earth orbit (LEO) systems,  MSAT uses  geostationary  earth
orbit satellites and spot beam technology to maximize coverage and capacity over
targeted geographic areas to provide unique business features, such as wide-area
dispatch services, which are not contemplated in current LEO system plans.




<PAGE>



American Mobile Satellite and TMI  Communications  use the world's most powerful
mobile  communications  satellite to offer a wide range of mobile communications
services including telephone,  digital broadcast dispatch,  data communications,
mobile messaging and position  reporting  services.  American Mobile Satellite's
shareholders  include Hughes  Communications,  Inc.; Singapore Telecom; and AT&T
Wireless  Services,  Inc. TMI is a limited  partnership  controlled by BCE Inc.,
Canada's largest telecommunications company.



Note: Factors that could cause  forward-looking  statements in this news release
to differ  materially  from actual  results  are  discussed  in American  Mobile
Satellite Corporation=s S-1 registration statement;  Form 10K for the year ended
December 31, 1996;  Form 10Q for the quarter ended September 30, 1997, and other
periodic  filings  the  company  has  made  with  the  Securities  and  Exchange
Commission.  Copies of the filings are available  upon request from the American
Mobile Satellite=s investor relations department.

American Mobile Satellite Contacts:

Media Contact:                       Orly Konig Lopez
703-716-6522

Investor Contact:                    Renate Brown Neely
703-716-6558

TMI Communications Contacts:

Marilynn Wright
613-748-8855

Daniel Tisch
416-920-9000, ext. 260
[email protected]


<PAGE>


                                                                 SCHEDULE 6.1(c)

<TABLE>
<CAPTION>

           DOCUMENTS RELATING TO THE CONDITION OF THE SHARED SATELLITE




<S>      <C>                                                                 <C> 
1        MSAT Health Report (Telesat)                                        June 12, 1997

2        MSAT Payload In-Orbit Test Report (Telesat)                         July 2, 1996

3        MSAT Bus In-Orbit Test Report (Telesat)                             October, 1996

4        MSAT West Central Beam Anomaly Investigation Review (Spar Draft)    November 26, 1996

5        MSAT M1 West-Central Beam Anomaly Investigation Summary Report      December 16, 1996

6        MSAT M1-WC Beam Anomaly (ID & Associates)                           January 8, 1997

7        MSAT M1 West-Central Beam Anomaly Report (Telesat)                  January 20, 1997

8        MSAT M1 West-Central Beam Test - Phase 1 Report (Telesat)           March 18, 1997

9        Mountain Beam Anomaly Presentation (Telesat)                        March 27, 1997

10       MSAT M1 West-Central Beam Investigation Report (Telesat)            March 31, 1997

11       MSAT West Central Beam EIRP Anomaly of April 17, 1997 (Telesat)     May 16, 1997

12       Letter from Spar to TMI Re:  Operating power levels for the M1 S    Julyc3,f1997

13       Review of MSAT M1 SSPA 4 and Carrier Monitoring Data (Spar)         September 12, 1997

14       MSAT Health Report (Telesat)                                        November 5, 1997


</TABLE>



<PAGE>


                                                                 SCHEDULE 6.1(f)
<TABLE>
<CAPTION>

                       EXISTING LIENS ON SHARED SATELLITE


<S>                        <C>                      <C>
Secured Party              Agreement                Nature and Amount of Secured Obligations
- -------------              ---------                ----------------------------------------

BCE Inc.                   Security Agreement,      Payment andperformance of all debts,liabilities
                           dated February 1,        and obligations, present or future, direct or 
                           1994 between BCE         indirect, absolute or contingent, matured or 
                           Inc. and TMI             unmatured, at any time due or accruing due by 
                                                    TMI to BCE Inc., however or wherever 
                                                    incurred, in any currency, and whether incurred
                                                    by TMI alone or with others and whether as 
                                                    principal or surety, together with other 
                                                    expenses, costs and charges as set out in the 
                                                    Security Agreement.

</TABLE>



<PAGE>
  


                                    EXHIBIT A
                               FORM OF CONVEYANCE


     This  conveyance  (this   "Conveyance")   dated  as  of             , 1997,
                                                             ____________
by TMI Communications and Company,  Limited  Partnership,  a limited partnership
organized under the laws of the Province of Quebec (the  "Assignor"),  to and in
favour of AMSC Subsidiary  Corporation,  a corporation dually incorporated under
the laws of the States of Delaware and Virginia, respectively (the "Assignee").

     WHEREAS this  Conveyance is delivered  pursuant to the  requirements of the
satellite  purchase  agreement dated as of December 2, 1997 between the Assignee
and the  Assignor  (the  "Agreement").  Capitalized  terms  used  herein and not
otherwise  defined  herein  shall  have the  meanings  ascribed  thereto  in the
Agreement.

     NOW THEREFORE,  in  consideration  of the premises and the mutual covenants
herein contained,  the  consideration  specified in the Agreement and other good
and  valuable  consideration,  the receipt and  sufficiency  of which are hereby
acknowledged,  the Assignor does hereby convey, grant,  bargain,  sell, transfer
and assign  unto the  Assignee,  its  successors  and  assigns,  a 50% legal and
beneficial undivided ownership interest in and to the Shared Satellite, free and
clear of all Liens,  except for and subject to the TMI Purchase  Money  Security
Interest.

     Except for the  representations and warranties of TMI set forth in Sections
6.1(c),  (f), (h), (i), (j), (k) and (l) of the  Agreement,  the interest in the
Shared Satellite transferred hereunder is on an "as is" basis. ACCORDINGLY,  ANY
AND ALL EXPRESS OR IMPLIED  WARRANTIES OR CONDITIONS  WITH RESPECT TO THE SHARED
SATELLITE  OR  ANY  PART  THEREOF,  ITS  CONDITION,   DURABILITY,   PERFORMANCE,
RELIABILITY,  EXPECTED LIFE OR SUITABILITY FOR ANY PARTICULAR USE INCLUDING, BUT
NOT LIMITED TO, WARRANTIES OR CONDITIONS OF  MERCHANTABILITY  OR FITNESS FOR ANY
PURPOSE  OR USE,  WHETHER  EXPRESSED  OR IMPLIED BY  CONTRACT,  TORT  (INCLUDING
NEGLIGENCE AND STRICT  LIABILITY),  STATUTE OR OTHER LEGAL THEORY, ARE EXPRESSLY
EXCLUDED AND DISCLAIMED.

     Nothing  contained in this  Conveyance  shall increase the liability of the
Assignor  to the  Assignee  beyond the  liability  that  Assignor  has under the
Agreement and any action brought by the Assignee with respect to this Conveyance
shall be subject to the limitations on liabilities and remedies set forth in the
Agreement.


<PAGE>




                                      - 2 -

     IN WITNESS WHEREOF,  the undersigned has executed this Conveyance effective
as of the date first written above.

                            TMI COMMUNICATIONS AND COMPANY, LIMITED PARTNERSHIP

                            By:   TMI COMMUNICATIONS INC.,
                                  its General Partner


                            By:   /s/________________________________
                                  Authorized Signing Officer


                            By:   /s/________________________________
                                  Authorized Signing Officer

                                  


<PAGE>

                                                                   SCHEDULE 1.1
                                  EXHIBIT B

                           FORM OF SECURITY AGREEMENT





                           AMSC SUBSIDIARY CORPORATION

                                   as Obligor



                                - in favour of -



               TMI COMMUNICATIONS AND COMPANY, LIMITED PARTNERSHIP







                               SECURITY AGREEMENT
                               --------------, 1997





<PAGE>




                               SECURITY AGREEMENT

     Security  agreement  dated  as of  the      day of                  ,  1997
made between AMSC  SUBSIDIARY  CORPORATION,  a corporation  dually  incorporated
under the laws of the States of Delaware and  Virginia,  respectively,  with its
principal  executive  office in Reston,  Virginia,  and TMI  COMMUNICATIONS  AND
COMPANY, LIMITED PARTNERSHIP,  a limited partnership organized under the laws of
the Province of Quebec.

     WHEREAS:

     A. The Obligor and TMI have entered into the Satellite  Purchase  Agreement
pursuant  to  which  TMI  has  agreed  to sell to the  Obligor  a 50%  undivided
ownership  interest in the Shared Satellite for the Satellite Purchase Price and
the  Obligor  has  agreed  to pay  certain  TT&C Fees to TMI in  respect  of the
operation of the Shared Satellite; and

     B. It is a condition  precedent  to the sale of a 50%  undivided  ownership
interest in the Shared Satellite and the satellite  sharing  arrangements  under
the Satellite  Purchase  Agreement  that TMI reserve out of the transfer of such
50% undivided ownership interest,  and the Obligor grant, a security interest in
AMSC's  interest  in the  Shared  Satellite  as  security  for the  payment  and
performance  to TMI of all debts,  liabilities  and  obligations  of the Obligor
under the Satellite  Purchase  Agreement,  all as more particularly set forth in
this Agreement;

     NOW  THEREFORE,  in  consideration  of the foregoing  premises,  the sum of
$10.00 in lawful  money of Canada now paid by TMI to the  Obligor and other good
and  valuable  consideration  (the  receipt  and  adequacy  of which are  hereby
acknowledged), the Obligor agrees as follows:

                                    ARTICLE 1
                                 INTERPRETATION

     Section 1.1  Definitions.  (1) As used in this  Agreement  and the recitals
hereto, the following capitalized terms have the following meanings:

     "Affiliate"  means,  with  respect to any Person,  any Person  controlling,
controlled  by or under common  control with such Person;  provided that neither
party hereto shall by reason of entering into the Satellite  Purchase  Agreement
or this Agreement and the consummation of the transactions  contemplated thereby
or hereby be an Affiliate  of the other party or of the entity or  entities,  if
any, through which the other party holds its Interests. For purposes hereof, the
term "control"  (including the terms  "controlling,"  "controlled by" and "under
common control with") means the possession,  direct or indirect, of the power to
direct  or cause the  direction  of the  management  and  policies  of a Person,
whether through the ownership of voting securities, by contract, or otherwise.

     "Agreement" means this security agreement and all schedules and instruments
in amendment or confirmation of it; "hereof", "hereto", "herein" and "hereunder"
and  similar  expressions  mean  and  refer  to  this  Agreement  and not to any
particular  Article  or  Section;  "Article"  or  "Section  " of this  Agreement
followed  by a number  means and refers to the  specified  Article or Section of
this Agreement.

     "Bankruptcy  Event"  with  respect  to a  Person  means  (i) the  voluntary
commencement  of any  proceeding,  or  voluntary  filing,  by such  Person  of a
petition seeking liquidation,  reorganization,  arrangement or readjustment,  in
any form,  of its debts  under  Title 11 of the United  States Code or under the
Bankruptcy and Insolvency Act (Canada) or under the Winding-Up and Restructuring
Act  (Canada) or under the  Companies'  Creditors  Arrangement  Act (Canada) (or
corresponding  provisions  of future laws of the United  States or of Canada) or
under any other  jurisdiction's  insolvency,  liquidation  or similar laws (each
such United States,  Canadian and other jurisdictions' laws being referred to as
a  "Bankruptcy  Law"),  or such  Person's  filing of an answer  consenting to or
acquiescing  in any such  petition,  or (ii) the  making  by such  Person of any
general  assignment  for the benefit of its  creditors or the  admission by such
Person in writing of its inability to pay its debts as they mature, or (iii) the
consent by such  Person to the filing of, the  failure by such Person to contest
successfully with respect to, or the granting of an order of relief with respect
to (x) any involuntary  petition or application under any Bankruptcy Law seeking
an  application  for  the  appointment  of  a  receiver,   trustee,   custodian,
sequestrator  or  similar  official  for the assets of such  Person,  or (y) any
involuntary   petition  or   application   under  any   Bankruptcy  Law  seeking
liquidation, reorganization,  arrangement or readjustment of its debts under any
Bankruptcy  Law,  or (iv) the  appointment  of a receiver,  trustee,  custodian,
sequestrator  or  similar  official  for the  assets  of such  Person  under any
Bankruptcy Law or otherwise.

     "Business Day" means a day which is not a Saturday, Sunday or legal holiday
on which  commercial  banking  institutions  in New York,  New York or Montreal,
Quebec are authorized to close.

     "Conveyance"  means  the  conveyance  to be  dated  as of the  date of this
Agreement by TMI to and in favour of the Obligor pursuant to which TMI conveys a
50% undivided  ownership interest in the Shared Satellite to the Obligor subject
to the  reservation  by TMI of, and the grant by the  Obligor  of, the  Purchase
Money Security Interest.

     "Enforcement  Notice"  means a  notice  which  may be given by TMI to AMSC,
whenever the Purchase Money Security Interest has become  enforceable,  that TMI
intends to exercise or enforce any remedy  which it may have  against AMSC under
the Security Agreement.

     "Enforcement  Period"  means the period  commencing on the date which is 30
days following the delivery of the Enforcement Notice.

     "Lien" means,  with respect to any asset, any mortgage,  lien (statutory or
otherwise),  pledge,  hypothecation,  charge, assignment, lease, title retention
agreement or arrangement,  security  interest or encumbrance of any kind, or any
other  security  agreement or  arrangement  creating in favour of any creditor a
right in respect of such asset that is prior to the right of any other  creditor
in respect of such asset.

     "Minimum  Satellite  Purchase  Price"  means the amount of  U.S.$60,000,000
payable by AMSC to TMI  pursuant  to Section  2.2(1) of the  Satellite  Purchase
Agreement.

     "Obligor"  means  AMSC  Subsidiary   Corporation,   a  corporation   dually
incorporated   under  the  laws  of  the  States  of  Delaware   and   Virginia,
respectively, and its successors and permitted assigns.

     "Permitted  Liens"  means,  with  respect to any  Person,  undetermined  or
inchoate liens,  privileges and charges  incurred and incidental to the ordinary
course of business  which  arise  solely by  operation  of law and have not been
filed  pursuant  to law against  such  Person or its assets and which  relate to
obligations which are not delinquent.

     "Person" means an individual, corporation, partnership, association, trust,
limited  liability  company or any other  entity or  organization,  including  a
court,   a  government  or  political   subdivision   or  an  agency,   unit  or
instrumentality thereof.

     "PPSA" means the Personal Property Security Act (Ontario),  as amended from
time to time.

     "Satellite Purchase Agreement" means the satellite purchase agreement dated
as of December 2, 1997  between  the Obligor and TMI, as such  agreement  may be
amended, modified,  extended,  renewed, replaced,  restated or supplemented from
time to time.

     "Satellite  Purchase  Price"  has  the  meaning  ascribed  thereto  in  the
Satellite Purchase Agreement.

     "Shared  Satellite"  means the satellite owned by TMI as of the date hereof
(and is referenced as the MSAT-1 (M1) satellite).

     "Shared  Satellite  Interest"  means the Obligor's 50% undivided  ownership
interest in the Shared  Satellite  acquired from TMI pursuant to the  Conveyance
subject  to the  reservation  by TMI of,  and the grant by the  Obligor  of, the
Purchase Money Security Interest.

     "TMI" means TMI Communications and Company, Limited Partnership,  a limited
partnership  organized  under  the  laws  of the  Province  of  Quebec,  and its
successors and permitted assigns.

     "TT&C Fees" means, collectively,  (i) the daily and monthly fees payable to
TMI by the  Obligor  pursuant  to  Section  3.1(2)  of  the  Satellite  Purchase
Agreement;  and (ii) such other  amounts  as are  payable  by AMSC  pursuant  to
Section 3.1(3) of the Satellite Purchase Agreement.

     (2) Terms  defined in the Personal  Property  Security Act (Ontario) (as in
effect as at the date of this  Agreement) and used in this Agreement  shall have
the same meaning in this agreement.

     (3) Each of the  following  terms  is  defined  in the  Section  set  forth
opposite such term:

<TABLE>
<CAPTION>

Term                                                    Section
- ----                                                    -------

<S>                                                     <C>   
Obligations                                             2.2(1)
Other Secured Party                                     2.4(1)(a)
Permitted User                                          2.4(3)
Purchase Money Security Interest                        2.2(1)
Satellite Collateral                                    2.1
Satellite Rights                                        2.1(a)
Subordination Clause                                    2.4(3)(a)

</TABLE>


     Section 1.2.  Gender and Number.  Any reference in this Agreement to gender
includes all genders and words  importing  the singular  number only include the
plural and vice versa.

     Section 1.3.  Headings,  etc. The division of this  Agreement into Articles
and Sections and the insertion of headings are for convenient reference only and
are not to affect the interpretation of this Agreement.

     Section  1.4.  Certain  Phrases,  etc.  In this  Agreement  (i)  the  words
"including" and "includes" mean  "including (or includes)  without  limitation",
and (ii) in the  computation of periods of time from a specified date to a later
specified date, unless otherwise  expressly stated,  the word "from" means "from
and including" and the words "to" and "until" each mean "to but excluding".

     Section 1.5.  Incorporation  of Schedules.  The schedules  attached to this
Agreement  shall,  for all purposes of this Agreement,  form an integral part of
it.


                                    ARTICLE 2
                                 INTERPRETATION

     Section 2.1 Purchase Money Security Interest. TMI hereby reserves to itself
out of the transfer to the Obligor of a 50% undivided  ownership interest in the
Shared Satellite contemplated under the Conveyance,  a security interest in, and
the  Obligor  hereby (i)  mortgages  and charges to TMI as and by way of a fixed
mortgage and charge;  (ii) pledges to TMI; (iii) assigns and transfers to TMI as
and by way of a  specific  transfer  and  assignment;  and (iv)  grants to TMI a
security interest in:

(a) all of the Shared  Satellite  Interest,  rights of use and other  intangible
rights now owned or  hereafter  acquired by the Obligor from TMI pursuant to the
Satellite  Purchase  Agreement  and the  Conveyance  and all  right,  title  and
interest of the Obligor in, to, under and in respect of the  Satellite  Purchase
Agreement,  all benefits,  powers and  advantages  of the Obligor  thereunder or
derived  therefrom and all services due or to become due to the Obligor under or
in connection with the Satellite Purchase Agreement  (collectively,  such Shared
Satellite  Interest and rights are referred to in this  Agreement as  "Satellite
Rights"); and

(b) all proceeds  derived  directly or indirectly from any sale,  lease or other
disposition of all or any part of the Satellite Rights;

provided,  however, that no security interest shall attach to customer contracts
entered into in the ordinary  course of business of the Obligor and the proceeds
thereof;

(collectively,  the property  described in the foregoing  paragraphs (a) and (b)
and each part thereof,  being  referred to in this  Agreement as the  "Satellite
Collateral").

     Section 2.2  Obligations  Secured.  (1) The interests  reserved  hereby and
under the  Conveyance  and the  charges,  pledges,  transfers,  assignments  and
security  interest  granted hereby  (collectively,  the "Purchase Money Security
Interest")  secure the payment and performance to TMI of all debts,  liabilities
and obligations,  present or future,  matured or unmatured,  at any time or from
time to time due or  accruing  due and owing by, or  otherwise  payable,  by the
Obligor to TMI arising out of, in  connection  with or pursuant to the Satellite
Purchase  Agreement  or this  Agreement  (collectively,  and  together  with the
expenses, costs and charges set out in Section 2.2(2), the "Obligations").

     (2) All  expenses,  costs and  charges  incurred  by or on behalf of TMI in
connection with the enforcement of its rights under this Agreement, the Purchase
Money  Security  Interest,  the  preservation  and  protection  of the Satellite
Collateral or the  realization of the Satellite  Collateral or the relocation of
the Shared  Satellite to a different  orbital  position (and the licensing  fees
payable  in  connection  therewith),  including  all legal  fees,  court  costs,
receiver's or agent's  remuneration and other expenses of taking  possession of,
repairing,   protecting,   insuring,   discharging  other  secured  liabilities,
preparing  for  disposition,   realizing,   collecting,  selling,  transferring,
delivering or obtaining  payment of the Satellite  Collateral  shall be added to
and form a part of the Obligations.

     Section 2.3  Attachment.  The Obligor and TMI hereby  acknowledge  that (i)
value has been given;  (ii) the Obligor has rights in the  Satellite  Collateral
(other than after-acquired Satellite Collateral);  (iii) they have not agreed to
postpone the time of attachment of the Purchase  Money  Security  Interest;  and
(iv) the Obligor has received a duplicate original copy of this Agreement.

     Section 2.4 Obligor's Dealings with Satellite  Collateral.  (1) The Obligor
shall not without the prior written consent of TMI:

(a) create,  assume or permit to be created or allow to subsist in favour of any
other  Person any Lien on the  Satellite  Collateral  except (x) the Obligor may
allow  to  subsist  any  Permitted  Lien  but  only  for so long  as  such  Lien
constitutes a Permitted Lien, and (y) the Obligor may create or allow to subsist
a Lien on the Satellite  Collateral in favour of any Person (the "Other  Secured
Party") which,  prior to any such creation or  subsistence,  has entered into an
agreement  with TMI, and TMI agrees to enter into such  agreement with the Other
Secured Party at such time, which provides for:

               (i) the  acknowledgement and agreement of the Other Secured Party
               that any and all of its rights in and to the Satellite Collateral
               are subject to and  subordinate  to the Purchase  Money  Security
               Interest and the rights of TMI in and to the Satellite Collateral
               reserved or granted  under this  Agreement  (irrespective  of the
               actual time, place of creation or order of execution, attachment,
               perfection, delivery, registration, filing or crystallization of,
               or other priority otherwise accorded under applicable law to, the
               Purchase Money Security  Interest and such Other Secured  Party's
               Lien,  the date or dates of default,  the date or dates of taking
               enforcement  proceedings  (including  possession),  the giving or
               failure  to give any notice to AMSC or any  failure  to  properly
               perfect or maintain the perfection of the Purchase Money Security
               Interest in the applicable jurisdiction) and that the proceeds of
               realization   arising  from  any  disposition  of  the  Satellite
               Collateral  shall be applied  first to the  amounts  owing to TMI
               under the Satellite Purchase Agreement and under this Agreement;

               (ii) the  agreement  of TMI that in the event  that the  Purchase
               Money Security  Interest shall become  enforceable  upon an event
               set forth in Section  3.1(a),  it shall notify the Other  Secured
               Party of such  default and if,  within 30 days of receipt of such
               notice,  the Other  Secured Party cures the default by payment to
               TMI of any and all overdue  amounts,  TMI will not accelerate the
               unpaid Satellite  Purchase Price, TT&C Fees and any other amounts
               owing  pursuant to the Satellite  Purchase  Agreement or commence
               realization  proceedings  under this Agreement in respect of that
               occurrence  of that event or issue any  Enforcement  Notice  (but
               such  waiver  by TMI of its  rights  in  respect  of any  payment
               default  will not extend to any  recurrence  of any such event or
               the  occurrence of any other event unless the Other Secured Party
               cures  any such  recurrence  or  occurrence  as set forth in this
               Section 2.4(1)(a)(ii)); and

               (iii) the  agreement  of TMI that in the event that the  Purchase
               Money Security  Interest shall become  enforceable  upon an event
               set  forth  in  Section  3.1(b),  TMI  will  not  accelerate  the
               remaining  TT&C  Fees and other  amounts  owing  pursuant  to the
               Satellite  Purchase  Agreement (but TMI may accelerate the unpaid
               Minimum  Satellite   Purchase  Price)  or  commence   realization
               proceedings under this Agreement in respect of that occurrence of
               that event or issue any Enforcement Notice so long as:

                    (A) the  Minimum  Satellite  Purchase  Price is paid in full
                    (whether or not then due under  Section 2.2 of the Satellite
                    Purchase Agreement) within 30 days of the occurrence of such
                    event specified in Section 3.1(b), and

                    (B)  all  TT&C  Fees  and  other  amounts  owing  under  the
                    Satellite Purchase Agreement are paid when due in accordance
                    with the Satellite  Purchase  Agreement or the Other Secured
                    Party  has  remedied  the  payment  default  as set forth in
                    Section 2.4(1)(a)(ii);

               (but such  waiver by TMI of its rights in respect of any  payment
               default  will not extend to any  recurrence  of any such event or
               the  occurrence of any other event unless the Other Secured Party
               cures  any such  recurrence  or  occurrence  as set forth in this
               Section 2.4(1)(a)(iii)); and

               (iv) the  agreement  of each of TMI and the Other  Secured  Party
               that it:

                    (A) will  provide the other with  copies of any  Enforcement
                    Notice  or any other  notice of  intention  to  enforce,  or
                    notice of exercise of, any of its  respective  remedies with
                    respect  to the  Satellite  Collateral  under  any  security
                    agreement  granted in its favour by AMSC within one Business
                    Day of delivery thereof to AMSC; and

                    (B) will use  reasonable  efforts to provide  the other with
                    copies  of any other  notice of  intention  to  enforce,  or
                    notice  of  exercise  of,  any of its  other  remedies  with
                    respect  to any other  collateral  subject  to any  security
                    agreement  granted in its favour by AMSC within one Business
                    Day of delivery thereof to AMSC but in no event shall either
                    party be liable to the other for any failure to provide such
                    other notices with respect to such other collateral; and

               (v) the  agreement  of TMI that in the  event  that the  Purchase
               Money Security  Interest shall become  enforceable  upon an event
               set forth in Section 3.1(b),

               (x) TMI will not issue an Enforcement  Notice or any other notice
               of intention  to enforce,  or notice of exercise of, any remedies
               under this Agreement nor commence  realization  proceedings under
               this  Agreement in respect of the  occurrence of that event or an
               event set forth in Section 3.1(a), and

               (y) any time periods  under any  Enforcement  Notice or any other
               notice of  intention  to enforce,  or notice of exercise  of, any
               remedies  under this  Agreement  issued prior to such event shall
               not run and be counted;

          so long as the Other  Secured  Party is stayed  or  restrained  in the
          United  States of America  by  operation  of law,  or is subject to an
          order of a court of  competent  jurisdiction  in the United  States of
          America which stays or restrains the Other Secured Party, from

                    (A) issuing any notice of intention to enforce, or notice of
                    exercise  of, any  remedies  under its  respective  security
                    agreement with AMSC, and

                    (B)  proceeding  with  the  realization  of  any  collateral
                    subject  to, and the other  exercise  of its other  remedies
                    under, its respective security agreement with AMSC; and

               (vi) the agreement of the Other Secured Party that it

                    (A) will not (i) assert in any  action,  suit or  proceeding
                    whatsoever  the  invalidity,   ineffectiveness   or  general
                    unenforceability of this Agreement or the Satellite Purchase
                    Agreement; and (ii) pursue or cooperate with any other party
                    to pursue  any such  action,  suit or  proceeding;  it being
                    understood  and  agreed  that  regardless  of the  validity,
                    effectiveness  and  enforceability  of this Agreement or the
                    Satellite  Purchase  Agreement as between the other  Secured
                    Party and TMI,  TMI shall have the  priorities  set forth in
                    Section 2.4(a)(i); and

                    (B) to the fullest  extent  permitted by law, (i) waives any
                    claim  which  it may  have,  in any  action  by way of suit,
                    foreclosure,  sale, quit claim, acceptance of a deed in lieu
                    of  foreclosure  or  proceeding  for  acceptance  by  TMI of
                    Satellite  Collateral in  satisfaction of the Obligations or
                    any other  proceeding  with  respect to  realization  of the
                    Satellite  Collateral,  that  the fair  market  value of the
                    Satellite  Collateral exceeds the amount of the Obligations;
                    (ii)  waives  and  renounces  any  right  to  object  to any
                    proposal  of TMI  to  accept  the  Satellite  Collateral  in
                    satisfaction  of  the  Obligations;  and  (iii)  waives  and
                    renounces  any right to claim for relief from  forfeiture or
                    to  claim  that  any  remedy  available  to  TMI  hereunder,
                    including the right to receive the  Satellite  Collateral in
                    satisfaction of the  Obligations,  constitutes a penalty and
                    agrees not to  participate  in or  cooperate  with any other
                    party to  pursue  any  such  claim  in any  action,  suit or
                    proceeding;  it being  understood and agreed that subject to
                    (x) the  rights to  remedy  defaults  provided  to the Other
                    Secured Party under any  agreement  entered into between TMI
                    and the Other Secured Party pursuant to this Section 2.4(a),
                    and (y) any rights under the Satellite Purchase Agreement to
                    which the Other Secured Party may be entitled to exercise by
                    virtue of the enforcement of the security  interest  granted
                    to it in all of  AMSC's  rights  thereunder,  TMI  shall  be
                    entitled to obtain the Shared  Satellite  Interest  upon any
                    event  set  forth  in  Section  3.1 in  satisfaction  of the
                    Obligations; or

(b) sell,  transfer,  assign,  exchange,  lease,  release, let waste, abandon or
otherwise  dispose  of all or any  part of the  Satellite  Collateral  provided,
however,  that the Obligor shall be able to enter into customer contracts in the
ordinary course of business except as otherwise provided under Section 2.4(3).

     (2) The Obligor may,  before the Purchase Money Security  Interest  becomes
enforceable,  without the consent of TMI sell the  Satellite  Collateral  to any
Person to whom the Satellite  Purchase Agreement is assigned in accordance with,
and subject to, the terms of the Satellite Purchase Agreement.

     (3) Except as otherwise  provided in Section 2.4(4), the Obligor shall not,
without the prior  written  consent of TMI,  sell,  lease,  license or otherwise
grant any Person (each a "Permitted  User") any interest in the Shared Satellite
Interest,  or any  dedicated  filters or  dedicated  frequency  on, or dedicated
rights of access  to, the  Shared  Satellite  except  pursuant  to an  agreement
evidencing such sale, license or other use between the Obligor and any Permitted
User which contains:

(a) an agreement by the Permitted  User to and in favour of the Obligor as agent
of and bare trustee for TMI that any and all of the  Permitted  User's rights in
and to the Satellite  Rights are subject and  subordinate  to the Purchase Money
Security  Interest  and the  rights  of TMI in and to the  Satellite  Collateral
granted under this Agreement (the "Subordination Clause"); and

(b) an  agreement  by the  Permitted  User that TMI is an  intended  third party
beneficiary of the  Subordination  Clause and TMI may enforce the  Subordination
Clause directly against the Permitted Lessee.

     (4) TMI  acknowledges  and  agrees  that  the  form of  customer  contracts
presently entered into by the Obligor  substantially in the form provided by the
Obligor to TMI prior to the date of the  Satellite  Purchase  Agreement  are not
required  to comply  with  Sections  2.4(3)(a)  and (b) and do not  require  the
consent of TMI;  further,  in the event that any change in the form of  customer
contracts or agreements  entered into in the ordinary  course of business may be
construed as being subject to Section 2.4(3), in lieu of complying with Sections
2.4(3)(a)  and (b), the Obligor may include in such  contracts or  agreements an
express  disclaimer  that  notwithstanding  any other term or  condition of such
contract  or  agreement,  the  customer  shall not acquire  any  proprietary  or
leasehold  interest in the Shared Satellite or the Shared Satellite  Interest or
in any part thereof,  including  any  proprietary  or leasehold  interest in any
filters, frequency or rights of access.

     (5) The  Obligor  hereby  agrees  to hold the  Subordination  Clause of any
Permitted User contained in any agreement  between the Obligor and the Permitted
User  evidencing  the  sale,  lease,  licence  or  other  use,  and any  express
disclaimer  contained in any customer contract referred to in Section 2.4(4), as
agent and bare trustee for TMI and to enforce all such  covenants in  accordance
with the directions of TMI.


                                    ARTICLE 3
                             DEFAULT AND ENFORCEMENT

     Section 3.1 Default.  The Purchase  Money  Security  Interest  shall be and
become  enforceable  against the Obligor in each and every one of the  following
events in accordance with the terms thereof:

(a) if the Obligor shall fail to pay the Minimum  Satellite  Purchase  Price (or
any  instalment  thereof) or any TT&C fees within 10 days after its receipt from
TMI of written notice of late payment; or

(b) any Bankruptcy Event with respect to the Obligor.

     Section 3.2 Remedies.  Whenever the Purchase  Money  Security  Interest has
become  enforceable,  TMI may realize  only upon the  Satellite  Collateral  and
enforce its rights by:

(a) entry onto any premises where  equipment  which transmits RF signals to, and
receives  RF  signals  from,  the  Shared  Satellite  for the  sole  purpose  of
terminating such transmissions or receptions;

(b) unilaterally  issuing  directions or commands to Telesat Canada or any other
operator  from time to time of the Shared  Satellite as if TMI were the absolute
owner of all of the Obligor's right,  title and interest in and to the Satellite
Collateral;

(c) entry into possession of any or all of the Satellite Collateral by any other
method permitted by law;

(d) seizure,  collection or enforcement of, or other dealing with, any or all of
the Satellite  Collateral in such manner,  on such terms and  conditions  and at
such times as TMI deems  advisable but subject to the provisions of the PPSA and
other applicable law or equity;

(e) sale, lease,  assignment,  grant of options to purchase or otherwise dispose
of and deliver any or all of the Satellite  Collateral (or contract to do any of
the above),  in one or more parcels at any public or private sale, on such terms
and conditions and at such prices as is commercially reasonable, and for cash or
on credit or for future delivery with or without assumption of any credit risk;

(f) collection of any proceeds arising in respect of the Satellite Collateral;

(g) the  appointment by instrument in writing of a receiver  (which term as used
in this  Agreement  includes a receiver and  manager) or agent of the  Satellite
Collateral;

(h) the  institution of proceedings in any court of competent  jurisdiction  for
the appointment of a receiver of the Satellite Collateral;

(i) the  institution of proceedings in any court of competent  jurisdiction  for
sale or foreclosure of the Satellite Collateral;

(j)  filing  proofs of claim  and other  documents  to  establish  claims in any
proceeding relating to the Obligor;

(k) the  institution of proceedings  in any court of competent  jurisdiction  or
before any regulatory  authority for the termination of any  transmissions to or
from the  Satellite  Collateral  and the  substitution  therefor with such other
transmissions as TMI may direct; and

(l)  elect to  retain  the  Satellite  Collateral  in full  satisfaction  of the
Obligations  in the  manner  authorized  or  permitted  under  the PPSA or other
applicable law;

(m) any other  remedy or  proceeding  with respect to the  Satellite  Collateral
authorized or permitted under the PPSA or otherwise by law or equity.

Except  as  otherwise  provided  in this  Agreement  or the  Satellite  Purchase
Agreement,  such  remedies may be exercised  from time to time  separately or in
combination and are in addition to and not in substitution  for any other rights
of TMI however  created.  TMI shall not be bound to exercise any right or remedy
under Sections 3.2 or 3.3, and the exercise of such rights and remedies shall be
without  prejudice to the rights of TMI in respect of the Obligations  including
the right to claim for any deficiency.

     Section 3.3 Additional Rights. In addition to the remedies of TMI set forth
in Section 3.2, TMI may whenever the Purchase Money Security Interest has become
enforceable:

(a) repair,  process,  modify, complete or otherwise deal with any or all of the
Satellite  Collateral  and  prepare  for  the  disposition  of any or all of the
Satellite Collateral, whether on the premises of the Obligor or otherwise;

(b) pay any liability  secured by any actual or  threatened  Lien against any or
all of the Satellite Collateral;

(c) borrow for the purpose of  maintaining,  preserving or protecting any or all
of the Satellite  Collateral  and mortgage,  charge,  pledge or grant a security
interest in any or all of the Satellite  Collateral,  whether or not in priority
to the Purchase Money Security Interest, to secure repayment; and

(d)  demand,  commence,  continue  or  defend  any  judicial  or  administrative
proceedings  for the purpose of  protecting,  seizing,  realizing  or  obtaining
possession  of any  or all of the  Satellite  Collateral,  and  give  valid  and
effectual receipts and discharges therefor.

     Section 3.4 Concerning the Receiver. Any receiver appointed by TMI shall be
vested with the rights and  remedies  which could have been  exercised by TMI in
respect  of  the  Satellite  Collateral.  The  identity  of  the  receiver,  any
replacement  thereof and any  remuneration  thereof shall be within the sole and
unfettered discretion of TMI.

     Section  3.5  Appointment  of  Attorney.  The  Obligor  hereby  irrevocably
appoints each of TMI and TMI Communications Inc., the general partner of TMI (or
any  successor  or assignee to or of TMI  Communications  Inc.) (and any officer
thereof)  as  attorney  of the  Obligor  (with  full power of  substitution)  to
exercise  in the name of and on behalf of the  Obligor,  during the  Enforcement
Period, any of the Obligor's right (including the right of disposal),  title and
interest in and to the Satellite Collateral including the execution, endorsement
and delivery of any agreements, documents, instruments, securities, documents of
title and chattel paper and any notices, receipts,  assignments or verifications
of the accounts. All acts of any such attorney are hereby ratified and approved,
and such attorney  shall not be liable for any act,  failure to act or any other
matter or thing in connection therewith, except for its own negligence or wilful
misconduct.  This appointment and power of  substitution,  being coupled with an
interest,   are  irrevocable  and  shall  not  terminate  upon  the  bankruptcy,
dissolution, winding up or insolvency of the Obligor.

     Section 3.6 Dealing with the Satellite  Collateral  and the Purchase  Money
Security Interest.  (1) TMI shall not be obliged to exhaust its recourse against
the Obligor or any other person or persons or against any other  security it may
hold in respect of the Obligations  before  realizing upon or otherwise  dealing
with the Satellite Collateral in such manner as TMI may consider advisable.

     (2) TMI may  grant  extensions  or  other  indulgences,  take  and  give up
securities,  accept  compositions,  grant  releases and discharges and otherwise
deal with the Obligor and with other parties,  sureties or securities as TMI may
see fit without  prejudice to the Obligations or the rights of TMI in respect of
the Satellite Collateral.

     (3) TMI shall not be (i) liable or accountable  for any failure to collect,
realize or obtain payment in respect of the Satellite Collateral;  (ii) bound to
institute  proceedings  for the purpose of collecting,  enforcing,  realizing or
obtaining  payment in respect of the Satellite  Collateral or for the purpose of
preserving  any  rights of TMI,  the  Obligor  or any other  parties  in respect
thereof;  (iii) responsible for any loss occasioned by any sale or other dealing
with the  Satellite  Collateral  or by the  retention  of or  failure to sell or
otherwise  deal  therewith;  and (iv) bound to protect the Satellite  Collateral
from depreciating in value or becoming worthless.

     Section 3.7 Standards of Sale.  Without  prejudice to the ability of TMI to
dispose of the Satellite Collateral, the Obligor agrees with TMI that so long as
the following dispositions are commercially reasonable in the circumstances:

(a) Satellite Collateral may be disposed of in whole or in part;

(b) Satellite Collateral may be disposed of by public auction,  public tender or
private contract, with or without advertising and without any other formality;

(c) any  purchaser  or lessee  of such  Satellite  Collateral  may be TMI or any
customer or Affiliate of TMI;

(d) a disposition of Satellite Collateral may be on such terms and conditions as
to credit or otherwise as is commercially reasonable; and

(e) TMI may  establish  an upset or  reserve  bid or  price  in  respect  of the
Satellite Collateral.

     Section 3.8 Dealings by Third  Parties.  (1) No person  dealing with TMI or
its respective  agents or a receiver shall be required (i) to determine  whether
the Purchase Money Security Interest has become  enforceable;  (ii) to determine
whether the powers which TMI or its respective agents are purporting to exercise
have become exercisable; (iii) to determine whether any money remains due to TMI
by  the  Obligor;   (iv)  to  determine  the  necessity  or  expediency  of  the
stipulations  and  conditions  subject to which any sale or lease shall be made;
(v) to determine the propriety or regularity of any sale or of any other dealing
by TMI with the Satellite  Collateral;  or (vi) to see to the application of any
money paid to TMI.

     (2) Any  purchaser  of the  Satellite  Collateral  from TMI shall hold such
Satellite Collateral absolutely,  free from any claim or right of whatever kind,
including any equity of  redemption,  of the Obligor,  which the Obligor  hereby
specifically waives (to the fullest extent permitted by law) as against any such
purchaser, all rights of redemption,  stay or appraisal which the Obligor has or
may have under any rule of law or statute now existing or hereafter adopted.

     Section 3.9 Non-extinguishment of Certain Obligations. The Obligor will not
remain liable for any Obligations that are outstanding  following realization of
the  Satellite  Collateral,  save and  except  for (i) any  expenses,  costs and
charges incurred by or on behalf of TMI and referred to in Section 2.2(2);  (ii)
any unpaid  Satellite  Purchase Price and TT&C Fees due (otherwise than upon any
acceleration  pursuant to Section 7.3(1) of the Satellite Purchase Agreement) up
to and including the date of the transfer or sale of the Satellite Collateral to
any  Person or the  acceptance  by TMI of the  Satellite  Collateral;  (iii) any
amounts  payable by the  Obligor  pursuant  to Section  7.8(4) of the  Satellite
Purchase  Agreement;  and (iv)  any  other  amounts  due by the  Obligor  to TMI
(otherwise than upon an acceleration pursuant to Section 7.3(1) of the Satellite
Purchase Agreement and except for the Satellite Purchase Price and TT&C Fees) up
to and including the date of the transfer or sale of the Satellite Collateral to
any Person or the acceptance by TMI of the Satellite Collateral.

     Section 3.10 Application of Proceeds and Duty to Account.  (1) All proceeds
of any of the Satellite  Collateral  received by TMI may be applied to discharge
or satisfy any expenses, Liens, borrowings,  taxes and other outgoings affecting
the Satellite  Collateral or which are considered  advisable by TMI to preserve,
maintain,  relocate  or  enhance  the  Satellite  Collateral  or to keep in good
standing  any Liens on the  Satellite  Collateral  ranking  in  priority  to the
Purchase Money Security  Interest.  The balance of such proceeds will be applied
on account of the Obligations.

     (2) Upon indefeasible  payment in full of all Obligations to TMI, TMI shall
pay over any surplus proceeds of disposition of the Satellite  Collateral to the
Obligor or such other Person as may be lawfully entitled to receive such surplus
or as any court of competent jurisdiction may otherwise direct.

     Section 3.11 Stay of Remedies. In the event that the Obligor gives a notice
to elect to transfer the Shared  Satellite  Interest to TMI under Section 7.8 of
the Satellite  Purchase  Agreement prior to the  commencement of the Enforcement
Period, all enforcement of remedies provided for in Sections 3.2, 3.3 and 3.5 of
this  Agreement and all time periods under notices given pursuant to Section 3.2
shall be stayed and shall not resume unless the transactions  contemplated under
Sections 7.8 of the Satellite Purchase Agreement are not completed in accordance
with the terms thereof.


                                    ARTICLE 4
              REPRESENTATIONS, WARRANTIES AND ADDITIONAL COVENANTS

     Section 4.1  Representations  and  Warranties.  The Obligor  represents and
warrants to TMI that:

(a) its principal  place of business and chief executive  office,  and the place
where it keeps  its  books  and  records,  is at the  address  specified  on the
signature page of this Agreement;

(b) the only name under which it conducts  its  business and the location of the
feeder link earth  stations from which  transmissions  are made to the Satellite
Collateral are set forth in Schedule "A" hereto; and

(c) no Lien,  security  agreement or other  agreement  evidencing an Lien or any
financing  statement  or other  notice  evidencing  any Lien  which  ranks or is
capable of  ranking  ahead of or pari passu  with the  Purchase  Money  Security
Interest, with respect to any or all of the Satellite Collateral,  exists (other
than  Permitted  Liens) or is  registered  on file or on  record  in any  public
office.

     Section   4.2   Survival   of   Representations    and   Warranties.    All
representations,  warranties and covenants made by the Obligor in this Agreement
are material,  will be considered to have been relied on by TMI and will survive
the execution and delivery of this  Agreement or any  investigation  made at any
time by or on behalf of TMI and any  disposition  or payment of the  Obligations
until repayment in full of the Obligations.

     Section 4.3 Further  Documentation.  The Obligor  shall,  from time to time
whether  before  or  after  the  Purchase  Money   Security   Interest   becomes
enforceable,  promptly  and duly  authorize,  execute and deliver  such  further
deeds, transfers, assignments,  instruments and documents, and take such further
action,  as TMI may request for the purpose of obtaining or preserving  the full
benefits of, and the rights and powers granted by, this Agreement (including the
filing of any financing  statements  or financing  change  statements  under any
applicable  legislation  with respect to the Purchase Money Security  Interest).
The Obligor  acknowledges  that this  Agreement has been  prepared  based on the
existing  laws of the  Province  of  Ontario  and the  States  of  Delaware  and
Virginia,  and that a change in such laws,  or the laws of other  jurisdictions,
may  require  the  execution  and  delivery  of  different   forms  of  security
documentation.  Accordingly,  the Obligor agrees that TMI will have the right to
require that this Agreement be amended or supplemented or replaced, and that the
Obligor will  immediately on request of TMI  authorize,  execute and deliver any
such amendment, supplement or replacement:

(a) to  reflect  any  changes  in such  laws,  whether  arising  as a result  of
statutory amendments, court decisions or otherwise;

(b) to facilitate the creation and  registration of appropriate  security in all
appropriate jurisdictions; or

(c) if the Obligor  merges or  amalgamates  with any other Person or enters into
any corporate reorganization;

in each case in order to confer on TMI a Lien  which is  similar  to,  and which
will have the same rights, priorities and effect as, the Purchase Money Security
Interest. The Obligor shall, from time to time after the Purchase Money Security
Interest  has become  enforceable,  do all such acts and things and  execute and
deliver all such deeds, transfers, assignments, instruments and documents as TMI
may require for facilitating the sale of the Satellite  Collateral in connection
with any realization thereof.

     Section 4.4 Notices.  The Obligor will promptly  notify TMI in writing,  in
reasonable detail, of any Lien (other than the Purchase Money Security Interest,
any  Permitted  Lien and any Lien  permitted  in  writing  by TMI) on,  or claim
asserted against, any of the Satellite  Collateral.  The Obligor will notify TMI
in writing,  in reasonable detail, of (i) any proposed change in the location of
any place of business or the chief  executive  office of the  Obligor;  (ii) any
proposed change in the location of any feeder link earth station or any proposed
additional  feeder link earth station  location from which  transmissions to the
Satellite Collateral may in the future originate;  and (iii) any proposed change
in the name of the  Obligor;  in each case,  at least 30 days before any of such
changes become effective.


                                    ARTICLE 5
                                     GENERAL

     Section 5.1  Discharge.  The  Purchase  Money  Security  Interest  shall be
discharged  upon, but only upon (i) at any time (x) prior to the commencement of
the  Enforcement  Period,  full  indefeasible  payment of the Minimum  Satellite
Purchase  Price and all TT&C Fees  owing as at the date of  payment of the final
instalment  of the  Minimum  Satellite  Purchase  Price,  or (y) on or after the
commencement  of  the  Enforcement  Period,  full  indefeasible  payment  of the
Obligations;  or (ii) the  transfer of the Shared  Satellite  Interest to TMI in
accordance with Section 7.8 of the Satellite  Purchase  Agreement;  and, in each
case,  (iii) the  request  in  writing  for such  discharge  and  payment of all
expenses in connection  therewith by the Obligor.  In furtherance  thereof,  TMI
shall,  at such time and at the  Obligor's  request  and  expense,  execute  and
deliver  to  the  Obligor  such  releases  and  discharges  as the  Obligor  may
reasonably require.

     Section 5.2 No Merger,  etc. No judgment  recovered by TMI shall operate by
way of merger of or in any way  affect the  Purchase  Money  Security  Interest,
which is in addition to and not in  substitution  for any other  security now or
hereafter held by TMI in respect of the Obligations.

     Section 5.3 Waivers,  etc. No amendment,  consent or waiver by TMI shall be
effective unless made in writing and signed by an authorized  officer of TMI and
then such  amendment,  waiver or consent shall be effective only in the specific
instance  and for the specific  purpose for which given.  No failure or delay on
the part of TMI in exercising any right under this Agreement  shall operate as a
waiver of, or impair,  any right of TMI  however  created.  No single or partial
exercise of a right  shall  preclude  any further  exercise of such right or the
exercise of any other right.

     Section 5.4  Successors and Assigns.  This Agreement  shall be binding upon
the  Obligor,  its  successors  and  permitted  assigns,  and shall enure to the
benefit  of  TMI  and  its  successors  and  permitted   assigns.   AMSC  hereby
acknowledges and consents to the grant by TMI to BCE Inc. of a security interest
in all of TMI's rights under the  Satellite  Purchase  Agreement  and under this
Agreement as security for the obligations  from time to time owing by TMI to BCE
Inc.,  and AMSC  hereby  agrees  that BCE Inc.  may  enforce  all  rights of TMI
hereunder and under the Satellite  Purchase Agreement upon the security interest
granted by TMI in favour of BCE Inc. becoming enforceable. TMI may assign all of
its rights and  obligations  hereunder  (i) to any Person to whom the  Satellite
Purchase  Agreement is assigned in accordance with, and subject to, the terms of
the  Satellite  Purchase  Agreement;  or (ii) to any other Person with the prior
written consent of the Obligor not to be unreasonably withheld.

     Section 5.5  Severability.  If any  provision  of this  Agreement  shall be
deemed  by any  court of  competent  jurisdiction  to be  invalid  or void,  the
remaining provisions shall remain in full force and effect.

     Section 5.6  Governing  Law.  (1) This  Agreement  shall be governed by and
interpreted  and enforced in accordance with the laws of the Province of Ontario
and the laws of Canada  applicable  therein and shall be treated in all respects
as an Ontario contract.

(2) The Obligor hereby (i) irrevocably  submits to the jurisdiction of any court
of  competent  jurisdiction  sitting in the  Province of Ontario  over any suit,
action  or  proceeding  arising  out of or  relating  to  this  Agreement;  (ii)
irrevocably  agrees  that all  claims in  respect  of any such  suit,  action or
proceeding may be heard and determined in such court; (iii) irrevocably  waives,
to the fullest  extent  permitted  by law,  any  objection  which it may have or
hereafter have to the laying of the venue of any such suit, action or proceeding
brought in such a court and any claim that any such suit,  action or  proceeding
brought in such a court has been  brought  in an  inconvenient  forum;  and (iv)
irrevocably  agrees that a final judgment in any such action or proceeding shall
be conclusive and may be enforced in any manner provided by law.

(3)  Nothing in this  Section  shall  affect  the right of the  parties to serve
process in any manner  permitted by law or, except as otherwise  provided  under
Section 5.6(2),  limit the right of the parties to bring proceedings against the
other parties in the courts of any other jurisdiction.

(4) Nothing in this Section shall  constitute a waiver by any party of any right
to (i) appeal any order or judgment  referred  to herein;  (ii) seek any stay or
reconsideration


<PAGE>

or review of any such order or judgment;  or (iii) seek any stay of execution or
levy  pending  any  appeal  from,   or  a  suit,   action  or   proceeding   for
reconsideration or review of, any such order or judgment.

     IN WITNESS  WHEREOF,  each of the  Obligor and TMI has duly  executed  this
Agreement  under the hands of its proper officers duly authorized in that behalf
as of the day and year first above written.


                             AMSC SUBSIDIARY CORPORATION


                             By:    
                             Name:  
                             Title: 


                             TMI COMMUNICATIONS AND COMPANY, LIMITED PARTNERSHIP

                             By:       TMI COMMUNICATIONS INC.,
                                       its General Partner


                             By:
                                        Authorized Signing Officer


                             By:
                                        Authorized Signing Officer

                                                                     


<PAGE>


                          
                                  SCHEDULE "A"

            BUSINESS NAMES AND LOCATION OF FEEDER LINK EARTH STATIONS


[AMSC to confirm all business names and locations as at Traffic Transfer Date]


Business Names:
- ---------------

American Mobile Satellite Corporation
AMSC Subsidiary Corporation
Skycell
MSAT



Locations of Feeder Link Earth Stations:
- ----------------------------------------

American Mobile Satellite Corporation
10802 Parkridge Blvd.
Reston, Virginia  22109

Washington International Teleport
5600 General Washington Drive
Alexandria, VA  22312

                                                                                


<PAGE>








Reference: 97- #22

FOR IMMEDIATE RELEASE

                          AMERICAN MOBILE SATELLITE TO
                  LEASE MSAT-2 SATELLITE TO NEW AFRICAN VENTURE

                     MSAT-1 Satellite to Serve US Customers

     RESTON,  VIRGINIA,  December 4, 1997--American Mobile Satellite Corporation
(NASDAQ:   SKYC)  will  lease  its  MSAT-2  satellite  to  African   Continental
Telecommunications  Limited  (ACTEL) for  deployment  over  sub-Saharan  Africa.
Through an agreement with TMI Communications of Ottawa, Canada,  American Mobile
Satellite  will  jointly own and  operate  the  identical  MSAT-1  satellite  to
continue to build its customer base for unique mobile communications services.

     The African  project is endorsed by key business and  political  figures in
the US and  Africa.  ACTEL's  board of  directors  and  advisors  includes  such
noteworthy  figures  as Andrew  Young,  former  mayor of  Atlanta  and former US
ambassador to the UN; Percy Sutton, former president of the Borough of Manhattan
and founder of Inner City Broadcasting; and Babacar N'Diaye, former president of
the African Development Bank.

     "American  Mobile  Satellite is  privileged  to  contribute  to this worthy
African venture," said Gary M. Parsons, president and chief executive officer of
American  Mobile  Satellite.  "The  transaction is financially  positive for our
company,  while  accelerating  development  of the business  and  communications
infrastructure of Africa."

     "The new  southern  African  communications  system  will bring much needed
communications  to mobile  users and remote  villages  previously  unreached  by
telephone  service  of any kind,  helping  to raise the  standard  of living and
increase  the  economic  development  of the  countries  served,"  said James R.
Walker, ACTEL chief executive officer. 

                                    - more -


<PAGE>


         Under the proposed  arrangement,  American Mobile  Satellite will lease
MSAT-2 to ACTEL for a five-year renewable lease with payments of $38 million per
year.  American Mobile Satellite will also license its ground station technology
to ACTEL. The lease income will be used by American Mobile Satellite to fund the
purchase of its share of the MSAT-1  satellite  and to further  develop its core
business by enhancing  service  offerings,  developing  more  advanced  customer
equipment and adding additional customers.

     American Mobile  Satellite  provides a wide range of mobile  communications
services including telephone,  digital broadcast dispatch,  data communications,
mobile messaging and position  reporting  services.  The company's  shareholders
include  Hughes  Communications,  Inc.;  Singapore  Telecom;  and AT&T  Wireless
Services, Inc.

                                       ###


Factors  that could cause  forward-looking  statements  in this news  release to
differ materially from actual results are discussed in American Mobile Satellite
Corporation's S-1 registration  statement;  Form 10K for the year ended December
31, 1996;  Form 10Q for the quarter ended  September 30, 1997 and other periodic
filings the company has made with the Securities and Exchange Commission. Copies
of the filings are available upon request from the American  Mobile  Satellite's
investor relations department.

American Mobile Satellite Contacts
Press Contact:             Orly Konig Lopez
                           703/716-6522

Investor Contact:          Renate Brown Neely
                           703/716-6558


ACTEL Contact

James R. (Jim) Walker
908/953-9659






<PAGE>




Reference: 97- #23

FOR IMMEDIATE RELEASE

                         TMI, AMERICAN MOBILE SATELLITE
               TEAM UP ON POWERFUL MOBILE COMMUNICATIONS SATELLITE

    Joint Ownership and Operation of MSAT Satellite to Benefit Both Companies

     OTTAWA, CANADA and RESTON,  VIRGINIA,  December 4, 1997--TMI Communications
and American Mobile Satellite  Corporation  (NASDAQ:  SKYC) today announced that
both  companies  will use the  powerful  MSAT-1  satellite to bring their mobile
communications services to customers.  Under an agreement signed today, American
Mobile  Satellite will buy a half interest in MSAT-1 from TMI, and the companies
will  share the costs of  satellite  operations.  The  agreement  is  subject to
regulatory approvals in Canada and the US.

     In a related  announcement  issued today by American Mobile Satellite,  the
twin MSAT-2 satellite will be leased to African  Continental  Telecommunications
Limited (ACTEL) and moved to provide service in southern Africa.

     "In North America,  MSAT mobile satellite  technology is well suited to the
needs  of  maritime,  government,  transportation,  utility,  and  oil  and  gas
industries,"  said Gary M.  Parsons,  president and chief  executive  officer of
American Mobile  Satellite.  "This agreement allows American Mobile Satellite to
develop  these  targeted  business  applications  while moving more quickly to a
second generation solution."

     Parsons' enthusiasm was echoed by Larry Boisvert, TMI's president and chief
executive officer.  "TMI wants to use the MSAT satellite to position the company
for success in the North American mobile communications  market," Boivsert said.
"By working with American  Mobile  Satellite,  TMI will be better  positioned to
serve and aggressively expand its customer base." 

                                    - more -


<PAGE>


         TMI and American  Mobile  Satellite are no strangers to doing  business
together.  Through a joint development and operating agreement,  they funded the
design and development of the unique MSAT mobile  satellite  technology.  During
1995 and 1996, TMI and American  Mobile  Satellite  placed twin MSAT  satellites
into service over Canada and the United States.  Unlike proposed low earth orbit
(LEO)  systems,  MSAT uses  geostationary  earth orbit  satellites and spot beam
technology to maximize  coverage and capacity over targeted  geographic areas to
provide unique business features, such as wide area dispatch services, which are
not contemplated in current LEO system plans.

         American Mobile Satellite and TMI  Communications  use the world's most
powerful  mobile  communications  satellite  to  offer a wide  range  of  mobile
communications  services including telephone,  digital broadcast dispatch,  data
communications,  mobile  messaging  and position  reporting  services.  American
Mobile Satellite's  shareholders include Hughes Communications,  Inc.; Singapore
Telecom;  and  AT&T  Wireless  Services,  Inc.  TMI  is  a  limited  partnership
controlled by BCE Inc., Canada's largest telecommunications company.


                                       ###


Factors  that could cause  forward-looking  statements  in this news  release to
differ materially from actual results are discussed in American Mobile Satellite
Corporation's S-1 registration  statement;  Form 10K for the year ended December
31, 1996;  Form 10Q for the quarter ended September 30, 1997, and other periodic
filings the company has made with the Securities and Exchange Commission. Copies
of the filings are available upon request from the American  Mobile  Satellite's
investor relations department.

American Mobile Satellite Contacts
Press Contact:             Orly Konig Lopez
                           703/716-6522

Investor Contact:          Renate Brown Neely
                           703/716-6558

TMI Contacts

Marilyn Wright
613-748-8855

Daniel Tisch, Environics Communications
416/920-9000
[email protected]


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