Exhibit 10.64b
                                                            --------------

                           AMSC SUBSIDIARY CORPORATION
                                    Term Note


$10,000,000                                                   New York, New York
                                                               December 30, 1997


                  FOR VALUE RECEIVED,  the undersigned,  a Delaware  corporation
dually  incorporated as a Virginia Public Service  corporation (the "Borrower"),
hereby PROMISES TO PAY to the order of HUGHES COMMUNICATIONS SATELLITE SERVICES,
INC., a Delaware  company (the "Lender"),  its successors or assigns,  in lawful
money of the United States of America and in immediately  available  funds,  the
amount of TEN MILLION DOLLARS  ($10,000,000)  (or, if less, the unpaid principal
amount of Loans made by Lender to the Borrower under the Loan Agreement referred
to  below)  on the  Maturity  Date and to pay  interest  from and after the date
hereof  on the  unpaid  principal  amount  hereof  at the rates and on the dates
provided in the Loan Agreement referred to below.

                  This Note is  issued  pursuant  to that  certain  Bridge  Loan
Agreement,  dated as of December 30, 1997, by and among the  Borrower,  American
Mobile  Satellite  Corporation  and Lender,  (as such  agreement may be amended,
modified or otherwise supplemented from time to time, the "Loan Agreement"), and
is  entitled to the benefit and  security  as  provided  for  therein,  to which
reference  is hereby  made for a  statement  of all of the terms and  conditions
under which the loans evidenced hereby are made. All capitalized  terms,  unless
otherwise  defined herein,  shall have the meanings ascribed to them in the Loan
Agreement.

                  If any  payment on this Note  becomes due and payable on a day
other than a Business  Day, the maturity  thereof  shall be extended to the next
succeeding  Business Day and,  with respect to payments of  principal,  interest
thereon shall be payable at the then applicable rate during such extension.

                  Upon and after the occurrence of an Event of Default,  without
demand,  notice or legal  process of any kind,  this Note may be  declared,  and
immediately shall become, or may automatically  (without any notice) become, due
and payable.

                  Demand,  presentment,  protest  and notice of  nonpayment  and
protest are hereby waived by the Borrower.





                  This Note has been  delivered  and  accepted at New York,  New
York and shall be interpreted, governed by and construed in accordance with, the
laws of the State of New York.

                                            AMSC SUBSIDIARY CORPORATION




                                            By:/s/Gary M. Parsons
                                               Name:  Gary M. Parsons
                                               Title: CEO, President