Registration No. 333-_____


                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                            ------------------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------

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

                                    Delaware
                         (State or other jurisdiction of
                         incorporation or organization)

                                   93-0976127
                      (IRS employer identification number)

                            10802 Parkridge Boulevard
                           Reston, Virginia 20191-5416
                                 (703) 758-6000
               (Address, including zip code, and telephone number,
                 including area code, of registrant's principal
                               executive offices)
                            ------------------------
                      American Mobile Satellite Corporation
               1999 Stock Option Plan for Non-employee Directors
                            (Full title of the Plan)
                            ------------------------

                                 Randy S. Segal
              Senior Vice President, General Counsel and Secretary
                      American Mobile Satellite Corporation
                            10802 Parkridge Boulevard
                           Reston, Virginia 20191-5416
                                 (703) 758-6000
            (Name, address and telephone number of Agent for Service)
                            ------------------------

                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
                                                 Amount           Proposed Maximum       Proposed Maximum       Amount of
           Title of securities                    to be            Offering Price       Aggregate Offering     Registration
             to be registered                Registered (1)        per Share (2)            Price (2)              Fee

<S>                                              <C>                  <C>                    <C>                  <C>
              Common Stock                       50,000               $13.3125               $665,625             $185.04

==========================================  =================  ====================== ======================  ==============
</TABLE>

(1)  With respect to the Plan, an additional  50,000 shares of the  registrant's
     common stock were registered on the registrant's  registration statement on
     Form  S-8  (File  No.  33-91714).

(2)  Estimated  solely  for the  purpose of  calculating  the  registration  fee
     pursuant to Rule 457(h) of the Securities Act of 1933, as amended.





<PAGE>



                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

         The documents containing the information  specified in Part I have been
and/or will be sent or given to  participants  as specified by Rule 428(b)(1) of
the Securities  Act of 1933, as amended (the  "Securities  Act").  In accordance
with the  instructions  to Part I of Form S-8, such  documents will not be filed
with the Securities and Exchange Commission (the "Commission") either as part of
this  Registration  Statement  or  as  prospectuses  or  prospectus  supplements
pursuant to Rule 424 of the Securities  Act.  These  documents and the documents
incorporated  by  reference  pursuant to Item 3 of Part II of this  registration
statement,  taken  together,  constitute  the  prospectus as required by Section
10(a) of the Securities Act.


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

         This registration statement registers additional shares of Common Stock
of  American  Mobile   Satellite   Corporation   (the  "Company")  for  which  a
registration  statement on Form S-8 relating to the Company's  Stock Option Plan
for  Non-employee  Directors is effective.  This  registration  statement hereby
incorporates by reference the contents of such earlier registration statement on
Form S-8 (File No.
33-91714).

Item 3.           Incorporation of Documents by Reference.

         The Company hereby  incorporates  by reference  into this  registration
statement the following documents filed by it with the Commission:

         (a)  The  Company's  Registration  Statement  on  Form  S-8  (File  No.
              33-91714);

         (b)  The  Company's  annual report  on Form  10-K  for the  year  ended
              December 31, 1998;

         (c)  The Company's quarterly  report on Form 10-Q for the quarter ended
              March 31, 1999;

         (d)  The Company's quarterly  report on Form 10-Q for the quarter ended
              June 30, 1999;

         (e)  The  Company's  current  report on Form 8-K dated June 7, 1999 and
              filed with the Commission on June 9, 1999;

         (f)  The  Company's  current  report on Form 8-K dated July 9, 199  and
              filed with the Commission on July 9, 1999;

         (g)  The  Company's  current  report on  Form  8-K  dated July 23, 1999
              and filed with the Commission on July 26, 1999;

         (h)  The Company's current report on Form 8-K dated October 5, 1999 and
              filed with the Commission on October 6, 1999; and

         (i)  The description of the Company's  common stock, par value $.01 per
              share ("Common  Stock"), contained  in  the Company's registration
              statement  on  Form 8-A, dated December 9, 1993 and on Form 8-A/A,
              dated December 13, 1993.





<PAGE>



         In addition,  all documents and reports filed by the Company subsequent
to the date  hereof  pursuant  to Sections  13(a),  13(c),  14, and 15(d) of the
Securities  Exchange Act of 1934, as amended (the "Exchange Act"),  prior to the
filing of a post-effective amendment which indicates that all securities offered
have been sold or which deregisters all securities  remaining  unsold,  shall be
deemed to be incorporated by reference in this registration  statement and to be
part hereof from the date of filing of such documents or reports.  Any statement
contained in a document  incorporated  or deemed to be incorporated by reference
herein  shall be  deemed to be  modified  or  superseded  for  purposes  of this
registration statement to the extent that a statement contained herein or in any
other  subsequently filed document which also is or is deemed to be incorporated
by reference herein modifies or supersedes such statement. Any such statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this registration statement.

Item 4.           Description of Securities.

         A  description  of  the  Company's  Common  Stock  is  incorporated  by
reference under Item 3.

Item 5.           Interests of Named Experts and Counsel.

         The legal  opinion with respect to the legality of the shares of Common
Stock being registered hereby, which opinion is being filed as Exhibit 5 to this
registration  statement,  is  being  provided  by Randy S.  Segal,  Senior  Vice
President,  General Counsel and Secretary of the Company. Ms. Segal owns 163,032
shares of common stock.  Her ownership  also includes  shares  issuable upon the
exercise of options  granted under the Company's Stock Option Plan which options
are vested and exercisable,  or which may be vested and exercisable within sixty
(60) days of the date of this registration statement.


Item 6.           Indemnification of Directors and Officers.

         The  Company's  Bylaws  provide  that the Company  will  indemnify  its
directors  and officers to the fullest  extent  permitted  by Delaware  law. The
Company  may  be  required  to  advance  litigation  expenses  in  the  case  of
stockholder  derivative actions or other actions,  against an undertaking by the
indemnified party to repay such advances if it is ultimately determined that the
indemnified party is not entitled to indemnification.

         In addition,  the Company's Certificate of Incorporation provides that,
pursuant to Delaware law, its directors shall not be liable for monetary damages
for breach of the directors'  fiduciary duty of care to the  corporation and its
stockholders.  This  provision  in the  Certificate  of  Incorporation  does not
eliminate the duty of care, and in appropriate  circumstances equitable remedies
such as injunctive or other forms of  nonmonetary  relief will remain  available
under  Delaware  law. In addition,  each director will continue to be subject to
liability for breach of the  director's  duty of loyalty to the Company for acts
or omissions not in good faith or involving intentional misconduct,  for knowing
violations  of law,  for  actions  leading to improper  personal  benefit to the
director,  and for payment of  dividends  or approval  of stock  repurchases  or
redemptions  that are unlawful  under  Delaware law. The provision also does not
affect a director's  responsibilities  under any other law,  such as the federal
securities laws.

         At present,  there is no pending litigation or proceeding  involving an
officer or director of the Company as to which  indemnification is being sought,
nor is the Company aware of any threatened  litigation that may result in claims
for indemnification by any officer or director.




<PAGE>





Item 7.           Exemption from Registration Claimed.

         Not applicable.

Item 8.                    Exhibits.

Exhibit Number                      Description

4.1                 Restated  Certificate  of  Incorporation  of the Company (as
                    restated effective September 7, 1999) (filed herewith).

4.2                 Amended and  Restated  Bylaws of the Company (as amended and
                    restated effective September 23, 1999) (filed herewith).

4.3                 Specimen  of  Common  Stock   Certificate   of  the  Company
                    (incorporated  by  reference  to  Exhibit  No.  4.1  to  the
                    Company's  Registration  Statement  on Form  S-1  (File  No.
                    33-70468)).

4.4                 American Mobile Satellite Corporation 1999 Stock Option Plan
                    for Non- Employee Directors (filed herewith).

4.5                 Form of Non-employee  Director Stock Option Agreement (filed
                    herewith).

5                   Opinion of Randy S. Segal,  Senior Vice  President,  General
                    Counsel  and  Secretary,   regarding  the  legality  of  the
                    securities being registered.

23.1                Consent of Randy S. Segal (included in Exhibit 5).

23.2                Consent  of  Arthur   Andersen   LLP,   independent   public
                    accountants.

23.3                Consent   of  KPMG   LLP,   independent   certified   public
                    accountants.

24                  Powers of Attorney (included on the signature pages hereof).



Item 9.                    Undertakings.

         The undersigned Registrant hereby undertakes:

                         (1) To file, during any period in which offers or sales
                  are   being  made,   a   post-effective   amendment   to  this
                  registration statement:

                               (i)  To  include  any   prospectus  required   by
                  Section 10(a)(3) of the Securities Act;

                               (ii) To reflect in  the  prospectus  any facts or
                  events arising after the  effective date  of the  registration
                  statement   (or  the   most  recent  post-effective  amendment
                  thereof)  which, individually or  in the aggregate,  represent
                  a  fundamental  change  in the  information  set  forth in the
                  registration statement;



<PAGE>




                                (iii)  To include any material information  with
                  respect to the plan of distribution  not previously  disclosed
                  in the  registration  statement or any material change to such
                  information in the registration statement.

                           provided,  however,  that  paragraphs  (a)(1)(i)  and
                  (a)(1)(ii)  do not apply if the  registration  statement is on
                  Form  S-3,  or Form  S-8 or  Form  F-3,  and  the  information
                  required to be included in a post-effective amendment by those
                  paragraphs  is  contained  in periodic  reports  filed with or
                  furnished  to the  Commission  by the  Registrant  pursuant to
                  Section  13 or  Section  15(d)  of the  Exchange  Act that are
                  incorporated by reference in the registration statement.

                           (2)  That,  for  the  purpose  of   determining   any
                  liability under the Securities  Act, each such  post-effective
                  amendment shall be deemed to be a new  registration  statement
                  relating to the securities  offered therein,  and the offering
                  of such  securities  at that  time  shall be  deemed to be the
                  initial bona fide offering thereof.

                           (3)  To  remove  from  registration  by  means  of  a
                  post-effective   amendment   any  of  the   securities   being
                  registered  which  remain  unsold  at the  termination  of the
                  offering.

     The  undersigned   Registrant  hereby  undertakes  that,  for  purposes  of
determining  any  liability  under  the  Securities  Act,  each  filing  of  the
Registrant's  annual  report  pursuant to Section  13(a) or Section 15(d) of the
Exchange Act (and, where  applicable,  each filing of an employee benefit plan's
annual  report   pursuant  to  Section  15(d)  of  the  Exchange  Act)  that  is
incorporated by reference in the Registration  Statement shall be deemed to be a
new registration  statement relating to the securities offered therein,  and the
offering of such  securities at that time shall be deemed to be the initial bona
fide offering thereof.

     Insofar as  indemnification  for liability arising under the Securities Act
may  be  permitted  to  directors,  officers  and  controlling  persons  of  the
Registrant pursuant to the foregoing  provisions,  or otherwise,  the Registrant
has been advised that in the opinion of the Commission such  indemnification  is
against  public  policy as expressed in the  Securities  Act and is,  therefore,
unenforceable.  In the  event  that a claim  for  indemnification  against  such
liabilities  (other than the payment by the  Registrant or expenses  incurred or
paid by a director,  officer or controlling  person in successful defense of any
action  ,  suit  or  proceeding)  is  asserted  by  such  director,  officer  or
controlling  person in connection  with the  securities  being  registered,  the
Registrant  will,  unless in the  opinion  of its  counsel  the  matter has been
settled by controlling precedent,  submit to a court of appropriate jurisdiction
the question of whether such  indemnification  by it is against public policy as
expressed in the Securities  Act and will be governed by the final  adjudication
of such issue.





<PAGE>



                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the undersigned
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized,  in the County of Fairfax,  Commonwealth  of Virginia,  on   October
12, 1999.

                                     AMERICAN MOBILE
                                     SATELLITE CORPORATION



                                      By:  /s/Walter V. Purnell, Jr.
                                           -------------------------
                                           Walter V. Purnell, Jr.
                                           President and Chief Executive Officer


                                POWER OF ATTORNEY

Know all men by these  presents,  that each individual  whose signature  appears
below  constitutes  and appoints  Gary M. Parsons,  Walter V. Purnell,  Jr., and
Randy S.  Segal,  and each of them,  his true and  lawful  attorney-in-fact  and
agent, with power of substitution and  resubstitution,  for him and in his name,
place and stead,  in any and all  capacities,  to sign a registration  statement
(the  "Registration  Statement")  relating to a registration of shares of common
stock on Form S-8 and to sign any and all amendments  (including  post-effective
amendments)  to the  Registration  Statement,  and to file  the  same,  with all
exhibits and other  documents in connection  therewith,  with the Securities and
Exchange Commission,  granting unto said  attorneys-in-fact and agents, and each
of them, full power and authority to do and perform each and every act and thing
requisite and  necessary to be done in and about the  premises,  as fully to all
intents and  purposes as he might or could do in person,  hereby  ratifying  and
confirming all that said  attorneys-in-fact and agents, or any of them, or their
or his substitutes or substitute,  may lawfully do or cause to be done by virtue
hereof.


         Pursuant  to the  requirements  of the  Securities  Act of  1933,  this
Registration  Statement  has been signed below by the  following  persons in the
capacities and on the dates indicated:


Signature                       Title                              Date


/s/Walter V. Purnell, Jr.       President and                October 12, 1999
-------------------------
Walter V. Purnell, Jr.          Chief Executive Officer


/s/W. Bartlett Snell            Senior Vice President and    October 12, 1999
--------------------
W. Bartlett Snell               Chief Financial Officer
                                (principal financial and
                                accounting officer)





<PAGE>





/s/Gary M. Parsons              Chairman of the              October 12, 1999
------------------
Gary M. Parsons                 Board of Directors


/s/Douglas I. Brandon           Director                     October 12, 1999
---------------------
Douglas I. Brandon


/s/Billy J. Parrott             Director                     October 12, 1999
-------------------
Billy J. Parrott

/s/Andrew A. Quartner           Director                     October 12, 1999
---------------------
Andrew A. Quartner

/s/Jack A. Shaw                 Director                     October 12, 1999
---------------
Jack A. Shaw
[{"type": "S-8", "sequence": "1", "description": "1999 NON-EMPLOYEE DIRECTOR STOCK OPTION PLAN", "secsgml_size_bytes": 19400}]
{"company-data": {"conformed-name": "AMERICAN MOBILE SATELLITE CORP", "cik": "0000913665", "assigned-sic": "4899", "irs-number": "930976127", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-88807", "film-number": "99726888"}, "business-address": {"street1": "10802 PARKRIDGE BLVD", "city": "RESTON", "state": "VA", "zip": "22091", "phone": "7037586000"}, "mail-address": {"street1": "10802 PARKRIDGE BLVD", "city": "RESTON", "state": "VA", "zip": "22091"}}
Registration No. 333-_____

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                            ------------------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------

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

                                    Delaware
                         (State or other jurisdiction of
                         incorporation or organization)

                                   93-0976127
                      (IRS employer identification number)

                            10802 Parkridge Boulevard
                           Reston, Virginia 20191-5416
                                 (703) 758-6000
               (Address, including zip code, and telephone number,
                 including area code, of registrant's principal
                               executive offices)
                            ------------------------
                      American Mobile Satellite Corporation
               1999 Stock Option Plan for Non-employee Directors
                            (Full title of the Plan)
                            ------------------------

                                 Randy S. Segal
              Senior Vice President, General Counsel and Secretary
                      American Mobile Satellite Corporation
                            10802 Parkridge Boulevard
                           Reston, Virginia 20191-5416
                                 (703) 758-6000
            (Name, address and telephone number of Agent for Service)
                            ------------------------

                         CALCULATION OF REGISTRATION FEE
Amount           Proposed Maximum       Proposed Maximum       Amount of
           Title of securities                    to be            Offering Price       Aggregate Offering     Registration
             to be registered                Registered (1)        per Share (2)            Price (2)              Fee
Common Stock                       50,000               $13.3125               $665,625             $185.04

==========================================  =================  ====================== ======================  ==============
(1)  With respect to the Plan, an additional  50,000 shares of the  registrant's
     common stock were registered on the registrant's  registration statement on
     Form  S-8  (File  No.  33-91714).

(2)  Estimated  solely  for the  purpose of  calculating  the  registration  fee
     pursuant to Rule 457(h) of the Securities Act of 1933, as amended.
PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

         The documents containing the information  specified in Part I have been
and/or will be sent or given to  participants  as specified by Rule 428(b)(1) of
the Securities  Act of 1933, as amended (the  "Securities  Act").  In accordance
with the  instructions  to Part I of Form S-8, such  documents will not be filed
with the Securities and Exchange Commission (the "Commission") either as part of
this  Registration  Statement  or  as  prospectuses  or  prospectus  supplements
pursuant to Rule 424 of the Securities  Act.  These  documents and the documents
incorporated  by  reference  pursuant to Item 3 of Part II of this  registration
statement,  taken  together,  constitute  the  prospectus as required by Section
10(a) of the Securities Act.

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

         This registration statement registers additional shares of Common Stock
of  American  Mobile   Satellite   Corporation   (the  "Company")  for  which  a
registration  statement on Form S-8 relating to the Company's  Stock Option Plan
for  Non-employee  Directors is effective.  This  registration  statement hereby
incorporates by reference the contents of such earlier registration statement on
Form S-8 (File No.
33-91714).

Item 3.           Incorporation of Documents by Reference.

         The Company hereby  incorporates  by reference  into this  registration
statement the following documents filed by it with the Commission:

         (a)  The  Company's  Registration  Statement  on  Form  S-8  (File  No.
              33-91714);

         (b)  The  Company's  annual report  on Form  10-K  for the  year  ended
              December 31, 1998;

         (c)  The Company's quarterly  report on Form 10-Q for the quarter ended
              March 31, 1999;

         (d)  The Company's quarterly  report on Form 10-Q for the quarter ended
              June 30, 1999;

         (e)  The  Company's  current  report on Form 8-K dated June 7, 1999 and
              filed with the Commission on June 9, 1999;

         (f)  The  Company's  current  report on Form 8-K dated July 9, 199  and
              filed with the Commission on July 9, 1999;

         (g)  The  Company's  current  report on  Form  8-K  dated July 23, 1999
              and filed with the Commission on July 26, 1999;

         (h)  The Company's current report on Form 8-K dated October 5, 1999 and
              filed with the Commission on October 6, 1999; and

         (i)  The description of the Company's  common stock, par value $.01 per
              share ("Common  Stock"), contained  in  the Company's registration
              statement  on  Form 8-A, dated December 9, 1993 and on Form 8-A/A,
              dated December 13, 1993.
In addition,  all documents and reports filed by the Company subsequent
to the date  hereof  pursuant  to Sections  13(a),  13(c),  14, and 15(d) of the
Securities  Exchange Act of 1934, as amended (the "Exchange Act"),  prior to the
filing of a post-effective amendment which indicates that all securities offered
have been sold or which deregisters all securities  remaining  unsold,  shall be
deemed to be incorporated by reference in this registration  statement and to be
part hereof from the date of filing of such documents or reports.  Any statement
contained in a document  incorporated  or deemed to be incorporated by reference
herein  shall be  deemed to be  modified  or  superseded  for  purposes  of this
registration statement to the extent that a statement contained herein or in any
other  subsequently filed document which also is or is deemed to be incorporated
by reference herein modifies or supersedes such statement. Any such statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this registration statement.

Item 4.           Description of Securities.

         A  description  of  the  Company's  Common  Stock  is  incorporated  by
reference under Item 3.

Item 5.           Interests of Named Experts and Counsel.

         The legal  opinion with respect to the legality of the shares of Common
Stock being registered hereby, which opinion is being filed as Exhibit 5 to this
registration  statement,  is  being  provided  by Randy S.  Segal,  Senior  Vice
President,  General Counsel and Secretary of the Company. Ms. Segal owns 163,032
shares of common stock.  Her ownership  also includes  shares  issuable upon the
exercise of options  granted under the Company's Stock Option Plan which options
are vested and exercisable,  or which may be vested and exercisable within sixty
(60) days of the date of this registration statement.

Item 6.           Indemnification of Directors and Officers.

         The  Company's  Bylaws  provide  that the Company  will  indemnify  its
directors  and officers to the fullest  extent  permitted  by Delaware  law. The
Company  may  be  required  to  advance  litigation  expenses  in  the  case  of
stockholder  derivative actions or other actions,  against an undertaking by the
indemnified party to repay such advances if it is ultimately determined that the
indemnified party is not entitled to indemnification.

         In addition,  the Company's Certificate of Incorporation provides that,
pursuant to Delaware law, its directors shall not be liable for monetary damages
for breach of the directors'  fiduciary duty of care to the  corporation and its
stockholders.  This  provision  in the  Certificate  of  Incorporation  does not
eliminate the duty of care, and in appropriate  circumstances equitable remedies
such as injunctive or other forms of  nonmonetary  relief will remain  available
under  Delaware  law. In addition,  each director will continue to be subject to
liability for breach of the  director's  duty of loyalty to the Company for acts
or omissions not in good faith or involving intentional misconduct,  for knowing
violations  of law,  for  actions  leading to improper  personal  benefit to the
director,  and for payment of  dividends  or approval  of stock  repurchases  or
redemptions  that are unlawful  under  Delaware law. The provision also does not
affect a director's  responsibilities  under any other law,  such as the federal
securities laws.

         At present,  there is no pending litigation or proceeding  involving an
officer or director of the Company as to which  indemnification is being sought,
nor is the Company aware of any threatened  litigation that may result in claims
for indemnification by any officer or director.
Item 7.           Exemption from Registration Claimed.

         Not applicable.

Item 8.                    Exhibits.

Exhibit Number                      Description

4.1                 Restated  Certificate  of  Incorporation  of the Company (as
                    restated effective September 7, 1999) (filed herewith).

4.2                 Amended and  Restated  Bylaws of the Company (as amended and
                    restated effective September 23, 1999) (filed herewith).

4.3                 Specimen  of  Common  Stock   Certificate   of  the  Company
                    (incorporated  by  reference  to  Exhibit  No.  4.1  to  the
                    Company's  Registration  Statement  on Form  S-1  (File  No.
                    33-70468)).

4.4                 American Mobile Satellite Corporation 1999 Stock Option Plan
                    for Non- Employee Directors (filed herewith).

4.5                 Form of Non-employee  Director Stock Option Agreement (filed
                    herewith).

5                   Opinion of Randy S. Segal,  Senior Vice  President,  General
                    Counsel  and  Secretary,   regarding  the  legality  of  the
                    securities being registered.

23.1                Consent of Randy S. Segal (included in Exhibit 5).

23.2                Consent  of  Arthur   Andersen   LLP,   independent   public
                    accountants.

23.3                Consent   of  KPMG   LLP,   independent   certified   public
                    accountants.

24                  Powers of Attorney (included on the signature pages hereof).

Item 9.                    Undertakings.

         The undersigned Registrant hereby undertakes:

                         (1) To file, during any period in which offers or sales
                  are   being  made,   a   post-effective   amendment   to  this
                  registration statement:

                               (i)  To  include  any   prospectus  required   by
                  Section 10(a)(3) of the Securities Act;

                               (ii) To reflect in  the  prospectus  any facts or
                  events arising after the  effective date  of the  registration
                  statement   (or  the   most  recent  post-effective  amendment
                  thereof)  which, individually or  in the aggregate,  represent
                  a  fundamental  change  in the  information  set  forth in the
                  registration statement;
(iii)  To include any material information  with
                  respect to the plan of distribution  not previously  disclosed
                  in the  registration  statement or any material change to such
                  information in the registration statement.

                           provided,  however,  that  paragraphs  (a)(1)(i)  and
                  (a)(1)(ii)  do not apply if the  registration  statement is on
                  Form  S-3,  or Form  S-8 or  Form  F-3,  and  the  information
                  required to be included in a post-effective amendment by those
                  paragraphs  is  contained  in periodic  reports  filed with or
                  furnished  to the  Commission  by the  Registrant  pursuant to
                  Section  13 or  Section  15(d)  of the  Exchange  Act that are
                  incorporated by reference in the registration statement.

                           (2)  That,  for  the  purpose  of   determining   any
                  liability under the Securities  Act, each such  post-effective
                  amendment shall be deemed to be a new  registration  statement
                  relating to the securities  offered therein,  and the offering
                  of such  securities  at that  time  shall be  deemed to be the
                  initial bona fide offering thereof.

                           (3)  To  remove  from  registration  by  means  of  a
                  post-effective   amendment   any  of  the   securities   being
                  registered  which  remain  unsold  at the  termination  of the
                  offering.

     The  undersigned   Registrant  hereby  undertakes  that,  for  purposes  of
determining  any  liability  under  the  Securities  Act,  each  filing  of  the
Registrant's  annual  report  pursuant to Section  13(a) or Section 15(d) of the
Exchange Act (and, where  applicable,  each filing of an employee benefit plan's
annual  report   pursuant  to  Section  15(d)  of  the  Exchange  Act)  that  is
incorporated by reference in the Registration  Statement shall be deemed to be a
new registration  statement relating to the securities offered therein,  and the
offering of such  securities at that time shall be deemed to be the initial bona
fide offering thereof.

     Insofar as  indemnification  for liability arising under the Securities Act
may  be  permitted  to  directors,  officers  and  controlling  persons  of  the
Registrant pursuant to the foregoing  provisions,  or otherwise,  the Registrant
has been advised that in the opinion of the Commission such  indemnification  is
against  public  policy as expressed in the  Securities  Act and is,  therefore,
unenforceable.  In the  event  that a claim  for  indemnification  against  such
liabilities  (other than the payment by the  Registrant or expenses  incurred or
paid by a director,  officer or controlling  person in successful defense of any
action  ,  suit  or  proceeding)  is  asserted  by  such  director,  officer  or
controlling  person in connection  with the  securities  being  registered,  the
Registrant  will,  unless in the  opinion  of its  counsel  the  matter has been
settled by controlling precedent,  submit to a court of appropriate jurisdiction
the question of whether such  indemnification  by it is against public policy as
expressed in the Securities  Act and will be governed by the final  adjudication
of such issue.
SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the undersigned
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized,  in the County of Fairfax,  Commonwealth  of Virginia,  on   October
12, 1999.

                                     AMERICAN MOBILE
                                     SATELLITE CORPORATION

                                      By:  /s/Walter V. Purnell, Jr.
                                           -------------------------
                                           Walter V. Purnell, Jr.
                                           President and Chief Executive Officer

                                POWER OF ATTORNEY

Know all men by these  presents,  that each individual  whose signature  appears
below  constitutes  and appoints  Gary M. Parsons,  Walter V. Purnell,  Jr., and
Randy S.  Segal,  and each of them,  his true and  lawful  attorney-in-fact  and
agent, with power of substitution and  resubstitution,  for him and in his name,
place and stead,  in any and all  capacities,  to sign a registration  statement
(the  "Registration  Statement")  relating to a registration of shares of common
stock on Form S-8 and to sign any and all amendments  (including  post-effective
amendments)  to the  Registration  Statement,  and to file  the  same,  with all
exhibits and other  documents in connection  therewith,  with the Securities and
Exchange Commission,  granting unto said  attorneys-in-fact and agents, and each
of them, full power and authority to do and perform each and every act and thing
requisite and  necessary to be done in and about the  premises,  as fully to all
intents and  purposes as he might or could do in person,  hereby  ratifying  and
confirming all that said  attorneys-in-fact and agents, or any of them, or their
or his substitutes or substitute,  may lawfully do or cause to be done by virtue
hereof.

         Pursuant  to the  requirements  of the  Securities  Act of  1933,  this
Registration  Statement  has been signed below by the  following  persons in the
capacities and on the dates indicated:

Signature                       Title                              Date

/s/Walter V. Purnell, Jr.       President and                October 12, 1999
-------------------------
Walter V. Purnell, Jr.          Chief Executive Officer

/s/W. Bartlett Snell            Senior Vice President and    October 12, 1999
--------------------
W. Bartlett Snell               Chief Financial Officer
                                (principal financial and
                                accounting officer)
/s/Gary M. Parsons              Chairman of the              October 12, 1999
------------------
Gary M. Parsons                 Board of Directors

/s/Douglas I. Brandon           Director                     October 12, 1999
---------------------
Douglas I. Brandon

/s/Billy J. Parrott             Director                     October 12, 1999
-------------------
Billy J. Parrott

/s/Andrew A. Quartner           Director                     October 12, 1999
---------------------
Andrew A. Quartner

/s/Jack A. Shaw                 Director                     October 12, 1999
---------------
Jack A. Shaw