AMERICAN MOBILE SATELLITE CORPORATION
                         1989 EMPLOYEE STOCK OPTION PLAN
                       As Amended Effective April 25, 1996




1.   Definitions

     In this Plan, except where the context otherwise  indicates,  the following
definitions apply:

     A.   "Agreement"  means a  written  agreement  implementing  a grant  of an
          Option  or an award of Bonus  Stock.

     B.   "Board" means the Board of Directors of the Corporation.

     C.   "Bonus Stock" means Shares  awarded under the Plan in accordance  with
          the terms of Article 9.

     D.   "Code" means the Internal Revenue Code of 1986, as amended.

     E.   "Committee"  means the committee of the Board meeting the standards of
          Rule  16b-3(c)(2)(i)  under the Exchange Act, or any similar successor
          rule,  appointed by the Board to administer the Plan. Unless otherwise
          determined by the Board, the Compensation Committee of the Board shall
          be the Committee.

     F.   "Common  Stock" means the common stock,  par value $.01 per share,  of
          the Corporation.

     G.   "Corporation" means AMERICAN MOBILE SATELLITE CORPORATION.

     H.   "Date of Exercise"  means the date on which the  Corporation  receives
          notice of the  exercise of an Option in  accordance  with the terms of
          Article 7.

     I.   "Date of Grant"  means the date as of which an Option is granted or an
          award of Bonus Stock is  authorized  by the action of the Committee or
          such later date as may be specified in the authorization.

     J.   "Employee"  means any  person  determined  by the  Committee  to be an
          employee of the Corporation or of a Subsidiary.

     K.   "Exchange Act" means the Securities Exchange Act of 1934, as amended.


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     L.   "Fair  Market  Value" of a Share means the amount equal to the average
          of the  high  and low  prices  of a Share  on the  applicable  date as
          reported  by the  consolidated  tape of the  National  Association  of
          Securities  Dealers  Automated  Quotation (or on such other recognized
          quotation  system on which the trading  prices of the Common Stock are
          quoted  on the  applicable  date),  or, if no Share  transactions  are
          reported on such tape (or such other system) on the  applicable  date,
          the high and low prices of a Share on the  immediately  preceding date
          on  which  Share  transactions  were  so  reported,  or as  determined
          pursuant to a reasonable method adopted by the Committee in good faith
          for such purpose.

     M.   "Grantee" means an Employee to whom bonus Stock has been awarded.

     N.   "Insider" means an Optionee or Grantee who is subject to the reporting
          requirements under Section 16(a) of the Exchange Act.

     O.   "Option" means an option to purchase  Shares granted under the Plan in
          accordance with the terms of Article 6.

     P.   "Option  Period"  means  the  period  during  which an  Option  may be
          exercised.

     Q.   "Option  Price"  means the  price per Share at which an Option  may be
          exercised.  The Option Price shall not be less than the greater of the
          Fair Market Value per Share  determined as of the Date of Grant or the
          par value of the Common Stock.

     R.   "Optionee" means an Employee to whom an Option has been granted.

     S.   "Plan" means this AMERICAN  MOBILE  SATELLITE  CORPORATION  1989 Stock
          Option Plan.

     T.   "Reload  Option"  means a new Option  granted to an Optionee  upon the
          surrender of Shares to pay the Option  Price of a  previously  granted
          Option.  The Option Price for any Reload Option shall not be less than
          the  greater  of the Fair  Market  Value  of a Share on the date  that
          Shares are  surrendered  in payment of the Option Price in  accordance
          with Section 3.A(d) or the par value of the Common Stock.  Other terms
          of the Reload  Option shall be the same as the terms  contained in the
          Optionee's Agreement relating to the Option being exercised.

     U.   "Share" means a share of Common Stock.

     V.   "Subsidiary"  means a corporation  at least 50% of the total  combined
          voting  power  of all  classes  of  stock  of  which  is  owned by the
          Corporation either directly or through one or more Subsidiaries.

     W.   "Withholding Tax Liabilities" means the Corporation's  federal,  state
          and any local  income  tax and  payroll  withholding  tax  obligations
          arising in  connection  with the exercise of an Option or the award of
          Bonus  Stock  under the Plan.  Withholding  Tax  Liabilities  does not
          include the Corporation's share of any payroll taxes.

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2.       Purpose

         The Plan is intended to assist in attracting and retaining Employees of
outstanding  ability and to promote the  identification  of their interests with
those of the shareholders of the Corporation.

3.       Administration

         The Plan shall be  administered  by the  Committee.  In addition to any
other  powers  granted to the  Committee,  it shall have the  following  powers,
subject to the express provisions of the Plan:

         A.  subject  to the  provisions  of  this  Plan,  to  determine  in its
discretion  the  Employees  to whom  Options  shall be granted and to whom Bonus
Stock  shall be  awarded,  the number of Shares to be subject to each  Option or
Bonus  Stock  award,  and the terms  upon  which  Options  may be  acquired  and
exercised and the terms and conditions of Bonus Stock awards;

         B. to determine  all other terms and  provisions of each  Agreement,
which need not be identical;

         C. without limiting the generality of the foregoing, to provide in its
discretion in an Agreement:

                 (a) for an  agreement  by the  Optionee  or  Grantee  to render
services to the  Corporation  upon such terms and conditions as may be specified
in the Agreement, provided that the Committee shall not have the power to commit
the Corporation to employ or otherwise retain any Optionee or Grantee;

                 (b) for restrictions on the transfer, sale or other disposition
of Shares  issued to the  Optionee  upon the  exercise of an Option or for other
restrictions permitted by Article 9 with respect to Bonus Stock;

                 (c) for an  agreement  by the  Optionee or Grantee to resell to
the Corporation,  under specified conditions, Shares issued upon the exercise of
an Option or awarded as Bonus Stock;

                 (d)  for  the  right  of  the  Optionee  to  surrender  to  the
Corporation  an Option (or a portion  thereof) that has become  exercisable  and
receive  upon such  surrender,  without  any  payment  to the  Corporation  or a
Subsidiary (other than amounts necessary to satisfy  Withholding Tax Liabilities
with  respect to the Option) that number of Shares  (equal to the highest  whole
number  of  Shares)  having an  aggregate  Fair  Market  Value as of the date of
surrender  equal to that  number of Shares  subject to the  Option  (or  portion
thereof)  being  surrendered  multiplied by an amount equal to the excess of (i)
the Fair Market Value of a Share on the date of  surrender  over (ii) the Option
Price,  plus an amount of cash equal to the Fair Market Value of any  fractional
Share to which the  Optionee  might be  entitled;  any such  surrender  shall be
treated as the exercise of the Option (or portion thereof); and

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                 (e)   for the automatic issuance of a Reload Option covering
a number of Shares equal to the number of any Shares used to pay the Option
Price;

         D. to construe and interpret the Agreements and the Plan;

         E. to require,  whether or not provided for in the pertinent Agreement,
of any person  exercising an Option or acquiring  Shares of Bonus Stock,  at the
time of such  exercise  or  acquisition,  the making of any  representations  or
agreements  which the  Committee  may deem  necessary  or  advisable in order to
comply with the securities laws or the United States or of any state; and

         F.  to make all other determinations  and  take  all  other actions
necessary or advisable for the administration of the Plan.

         Any  determinations or actions made or taken by the Committee  pursuant
to this  Article  shall,  subject to the  express  provisions  of this Plan,  be
binding and final.

4.       Eligibility

         Options  and Bonus Stock may be granted or awarded  only to  Employees,
provided,  however,  that members or the  Committee  are not eligible to receive
Options or Bonus Stock.  Subject to the  limitations of Section 5.A, an Employee
who has been granted an Option or Bonus Stock may be granted  additional Options
or Bonus Stock.

5.       Stock Subject to the Plan

         A.  Subject to  adjustment  as provided in Article 11, an  aggregate of
2,000,000  authorized and unissued Shares,  reissued  treasury Shares, or Shares
otherwise  acquired by the  Corporation,  may be issued  under the Plan upon the
exercise  of Options or pursuant to awards of Bonus  Stock,  provided,  however,
that no Employee may be granted  Options and awarded  Bonus Stock  covering more
than 50% of the number of Shares issuable under the Plan.

         B. If an Option  expires or terminates  for any reason  without  having
been fully exercised, or if Shares of Bonus Stock are forfeited, the unpurchased
Shares  which had been  subject to the Option at the time of its  expiration  or
termination,  or the forfeited Shares of Bonus Stock, shall become available for
the grant of other Options or for the award of additional Shares of Bonus Stock,
provided,  that in the case of forfeited  Shares and to the extent  necessary to
satisfy the  provisions  of Rule 16b-3 under the  Exchange  Act, the Grantee has
received no dividends prior to forfeiture with respect to such Shares.

6.       Options

         A. Subject to  the provisions  of this Plan,  the Committee  is hereby
authorized to grant Options to Employees.

         B. All Agreements  granting  Options shall contain a statement that the
Option is intended to be a nonstatutory  stock option and not an incentive stock
option as defined in section 422 of the Code.

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         C.  The  Option  Period  shall  be  determined  by  the  Committee  and
specifically set forth in the Agreement, provided, however, that an Option shall
not be  exercisable  before six months from the Date of Grant  (except that this
limitation  need not apply in the event of the death of the Optionee  within the
six-month  period) and no Option shall be exercisable  after ten years after the
Date of Grant.

         D. By accepting  the grant of an Option under the Plan,  each  Optionee
agrees,  for the Optionee and his or her successors,  that the Option may not be
exercised  at  any  time  that  the  Corporation  does  not  have  in  effect  a
registration statement under the Securities Act of 1933, as amended, relating to
the offer of Common Stock to the Optionee under the Plan, unless the Corporation
agrees to permit such exercise,  and that,  upon the issuance of any Shares upon
the  exercise  of the  Option,  the  Optionee  will,  upon  the  request  of the
Corporation,  agree in  writing  that he or she is  acquiring  such  Shares  for
investment only and not with a view to resale, and that he or she will not sell,
pledge or  otherwise  dispose of such Shares so issued  unless and until (i) the
Corporation  is  furnished  with  an  opinion  of  counsel  to the  effect  that
registration  of such Shares pursuant to the Securities Act of 1933, as amended,
is not required by that Act and the rules and regulations  thereunder;  (ii) the
staff of the Securities and Exchange  Commission has issued a "no-action" letter
with respect to such disposition;  or (iii) such registration or notification as
is, in the  opinion  of counsel  for the  Corporation,  required  for the lawful
disposition  of such  Shares  has been filed by the  Corporation  and has become
effective;  provided,  however,  that the Corporation  shall not be obligated to
file any such registration or notification.  The Option shall further agree that
the Company may place a legend  embodying such  restriction on the  certificates
evidencing such shares.

         E.  All  other  terms  of  Options  granted  under  the  Plan  shall be
determined by the Committee in its sole  discretion,  as exercised  consistently
with  the  terms of the  Plan,  and  specifically  set  forth in the  Optionee's
agreement.  Any terms of Options  determined by the Committee that vary from the
express terms set forth in the Plan also shall be specifically  set forth in the
Optionee's Agreement.


7.       Exercise

         A. An Option may,  subject to the  provisions  of the  Agreement  under
which it was  granted,  be  exercised in whole or in part by the delivery to the
Corporation of written notice of the exercise, in such form as the Committee may
prescribe,  accompanied  by full payment of the Option Price for the Shares with
respect to which the Option is exercised in accordance  with Section 7.B, and by
satisfaction  by the Optionee of Withholding  Tax Liabilities in accordance with
Article 10.

         B. The  Option  Price  may be paid in the form of (i)  cash,  which may
include an  assignment  of the right to  receive  cash  proceeds  of the sale of
Common  Stock  subject to the Option  pursuant to a "cashless  exercise"  of the
Option  through a transaction  with a broker,  (ii) duly  endorsed  certificates
representing Shares (other than Shares that are subject to a substantial risk of
forfeiture) having a Fair Market Value on the Date of Exercise aggregating

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not more than the  portion of the Option  Price  being paid by  delivery of such
Shares, or (iii) a combination of cash and Shares as provided in Sections 7.B(i)
and (ii).

         C.  To  the  extent   required  to  comply  with  Treasury   Regulation
ss.1.401(k)-  1(d)(2)(iv)(B)(4),  or any  amendment  or  successor  thereto,  an
Optionee's  "elective  and employee  contributions"  (within the meaning of such
Treasury  Regulation)  under the Plan shall be suspended  for a period of twelve
months  following such  Optionee's  receipt of a hardship  distribution  made in
reliance on such Treasury Regulation from any plan containing a cash or deferred
arrangement  under Section 401(k) of the Code maintained by the Corporation or a
related  party within the  provisions  of  subsections  (b),  (c), (m) or (o) of
Section 414 of the Code.

8.       Nontransferability

         Options granted under the Plan shall not be transferable otherwise than
(a) by will or the  laws of  descent  and  distribution,  or (b)  pursuant  to a
qualified  domestic  relations order as defined in Section 414(p) of the Code or
Title I of the Employee  Retirement Income Security Act or the rules thereunder,
and an Option may be  exercised,  during the  Optionee's  lifetime,  only by the
Optionee or, in the case of the Optionee's legal  disability,  by the Optionee's
legal representative.

9.       Bonus Stock

         A. Subject to the  provisions of this  Plan, the Committee  is  hereby
authorized to award Bonus Stock to Employees.

         B. Bonus  Stock  shall be Shares  that  shall be issued at such  times,
subject to  achievement  of such  performance  or other  goals and on such other
terms and conditions as the Committee shall deem appropriate.

10.      Satisfaction of Withholding Tax Liabilities

         Each Optionee or Grantee must provide the Corporation with the means to
satisfy the  Corporation's  Withholding  Tax  Liabilities,  with  respect to any
income  recognized  by the Optionee or Grantee as a result of the exercise of an
Option or award of Bonus Stock. Unless otherwise determined by the Committee and
specifically  set forth in the Optionee's or Grantee's  Agreement,  an Option or
Grantee may satisfy  Withholding  Tax  Liabilities by (i) delivering cash to the
Corporation,  (ii)  electing to have the  Corporation  retain  Shares  otherwise
issuable  on the  exercise of the Option or pursuant to the award of Bonus Stock
(other than Shares that are subject to a substantial risk of forfeiture),  (iii)
delivering  shares (other than Shares that are subject to a substantial  risk of
forfeiture)  to the  Corporation,  or (iv) electing to satisfy  Withholding  Tax
Liabilities  through a combination of clauses (i), (ii) or (iii) of this Article
10. Satisfaction of Withholding Tax Liabilities also shall be accomplished under
such  additional   reasonable  terms  and  conditions  as  the  Committee  deems
appropriate.  Unless otherwise  determined by the Committee and specifically set
forth in the  Optionee's or Grantee's  Agreement,  in the case of an Insider who
elects to satisfy  Withholding Tax Liabilities by having the Corporation  retain
Shares otherwise issuable on the exercise of an Option or pursuant to an award

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to Bonus Stock,  the Insider shall have the right to so satisfy  Withholding Tax
Liabilities  through  (a) an  irrevocable  election  made at least six months in
advance of the date on which the Withholding Tax Liabilities  arise,  and (b) if
the  Withholding  Tax  Liabilities  arise  during  the ten  business  day period
beginning  on the  third  business  day  following  the  public  release  of the
Corporation's  quarterly or annual earnings  ("Window  Period"),  an irrevocable
election made during such Window Period.




11.      Capital Adjustments

         The number and class of Shares  subject to each  outstanding  Option or
award of Bonus  Stock,  the Option Price and the  aggregate  number and class of
Shares for which  grants or awards  thereafter  may be made  shall be  equitably
adjusted  by the  Committee  to reflect  such events as stock  dividends,  stock
splits, extraordinary cash dividends, adoption of stock rights plans, split-ups,
split-offs,  spin-offs,  liquidations,   combinations  or  exchange  of  shares,
recapitalizations,  mergers,  consolidations,  reorganizations  or  any  similar
transaction of or by the Corporation.

12.      Termination or Amendment

         The Board shall have the power to terminate the Plan and to amend it in
any respect, provided that, after the Plan has been approved by the shareholders
of the Company,  the Board may not,  without the approval of the shareholders of
the Company if such approval is then required by applicable  law or in order for
the Plan to  continue  to  satisfy  the  requirements  of Rule  16b-3  under the
Exchange Act,  amend the Plan so as to increase  materially the number of Shares
that may be issued  under the Plan (except as provided in Article 11), to modify
materially the requirements as to eligibility for  participation in the Plan, or
to increase  materially the benefits accruing to participants under the Plan. No
termination  or amendment of the Plan shall,  without his or consent,  adversely
affect the rights or obligations of any Optionee or Grantee.

13.      Modification, Extension and Renewal of Options and Bonus Stock

         Subject to the terms and conditions  and within the  limitations of the
Plan, the Committee may modify,  extend or renew outstanding  Options, or accept
the surrender of outstanding  Options (to the extent not theretofore  exercised)
granted under the Plan or under any other plan of the Corporation,  or a company
or similar entity acquired by the Corporation or a Subsidiary, and authorize the
granting of new Options (to the extent not theretofore  exercised),  pursuant to
the Plan in  substitution  therefor  and the  substituted  Options may specify a
lower  exercise  price  than the  surrendered  Options,  a longer  term than the
surrendered  Options or have any other  provisions  that are  authorized  by the
Plan.  Subject to the terms and  conditions  and within the  limitations  of the
Plan, the Committee may modify the terms of any outstanding  Agreement providing
for an  award  of  Bonus  Stock.  Notwithstanding  the  foregoing,  however,  no
modification  of an Option  granted  under the Plan, or an award of Bonus Stock,
shall,  without the consent of the  Optionee or Grantee,  alter or impair any of
the Optionee's or Grantee's right or obligations.

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14.      Effectiveness of the Plan

         The Plan and any amendments requiring  shareholder approval pursuant to
Article  12  are  subject  to  approval  by  vote  of  the  shareholders  of the
Corporation within 12 months after their adoption by the Board.  Subject to that
approval,  the Plan and any  amendments  are effective on the date on which they
are  adopted by the  Board.  Options  and Bonus  Stock may be granted or awarded
prior to shareholder approval of the Plan or amendments, but each such Option or
Bonus  Stock  grant or award  shall be  subject to the  approval  of the Plan or
amendments  by the  shareholders.  Except to the extent  required to satisfy the
requirements  of Rule 16b-3 under the Exchange Act, the date on which any Option
or Bonus Stock granted or awarded prior to  shareholder  approval of the Plan or
amendment  is granted or awarded  shall be the Date of Grant for all purposes as
if the Option or Bonus Stock had not been subject to approval.  No Option may be
exercised prior to such shareholder approval,  and any Bonus Stock awarded shall
be forfeited if such shareholder approval is not obtained.

15.      Term of the Plan

         Unless sooner  terminated by the Board pursuant to Article 12, the Plan
shall  terminate  on  December  6, 2003,  and no  Options or Bonus  Stock may be
granted after termination.  The termination shall not affect the validity of any
Options or Bonus Stock may be granted after  termination.  The termination shall
not affect the validity of any Option or Bonus stock  outstanding on the date of
termination.

16.      Indemnification of Committee

         In addition to such other rights of indemnification as they may have as
Directors or as members of the Committee,  the members of the Committee shall be
indemnified  by the  Corporation  against  the  reasonable  expenses,  including
attorneys' fees, actually and reasonably incurred in connection with the defense
of any action, suit or proceeding,  or in connection with any appeal therein, to
which  they or any of them  may be a party  by  reason  of any  action  taken or
failure to act under or in connection with the Plan or any Option or Bonus Stock
granted or awarded hereunder, and against all amounts reasonably paid by them in
settlement  thereof  or paid by them in  satisfaction  or  judgment  in any such
action, suit or proceeding,  if such members acted in good faith and in a manner
which they  believed  to be in, and not opposed  to, the best  interests  of the
Corporation.

17.      General Provisions

         A. The establishment of the Plan shall not confer upon any Employee any
legal or equitable  right against the Corporation, any  Subsidiary  or  the
Committee, except as expressly provided in the Plan.

         B. The Plan does not  constitute  inducement or  consideration  for the
employment of any Employee,  nor is it a contract  between the  Corporation or a
Subsidiary  and any  Employee.  Participation  in the  Plan  shall  not  give an
Employee  any  right  to be  retained  in  the  service  of the  Corporation  or
Subsidiary.

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         C. The Corporation and is Subsidiaries may assume options, warrants, or
rights to purchase stock issued or granted by other  corporations whose stock or
assets shall be acquired by the  Corporation or a Subsidiary,  or which shall be
merged into or consolidated  with the  Corporation or a Subsidiary.  Neither the
adoption of this Plan, nor its submission to the shareholders, shall be taken to
impose any  limitations  on the powers of the  Corporation  or its affiliates to
issue,  grant, or assume options,  warrants,  rights, or bonus stock,  otherwise
than under this Plan,  or to adopt other stock option stock or bonus stock plans
or to impose any requirement of shareholder approval upon the same.

         D. The interests of any Employee under the Plan are not subject to the
claims of creditors  and  may  not, in any  way, be assigned, alienated or
encumbered except as provided in Article 8.

         E. The Plan  and each  Agreement shall  be governed, construed  and
administered in accordance with the laws of the State of Delaware.

         F. The adoption of the Plan,  the grant and exercise of Options and the
award of Bonus  Stock  shall be subject to  receipt of all  required  regulatory
approvals,  including without  limitation any required  approvals of the Federal
Communications Commission.

         G. Should any provision of the Plan that is intended to comply with the
provisions  of Rule 16b-3 under the  Exchange Act at the date of the adoption of
the Plan by the Board not be necessary for such compliance,  or become no longer
necessary for such compliance, such provision of the Plan shall have no force or
effect  under the Plan as of the date that such  provision  is not  required for
purpose of satisfying the provisions of Rule 16b-3 under the Exchange Act.


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