AMENDMENT NO. 1 TO RESELLER AGREEMENT

   1
                                                                 EXHIBIT 10.20.1

                                AMENDMENT NO.  1
                                       TO
                               RESELLER AGREEMENT

           This Amendment No. 1 to Reseller Agreement ("Amendment No. 1") is
made and entered into as of this 2nd day of September, 1997 by and among
ORBCOMM USA, L.P. ("ORBCOMM USA") and Orbital Sciences Corporation ITS Group
("Reseller").

                                   WITNESSETH

           WHEREAS, ORBCOMM USA and Reseller previously entered into a Reseller
Agreement dated as of March 3, 1997 (the "Reseller Agreement"); and

           WHEREAS, ORBCOMM USA and Reseller desire to amend and modify certain
terms of the Reseller Agreement;

           NOW, THEREFORE, the parties agree as follows:

           SECTION 1 Terms used but not otherwise defined herein shall have the
meanings assigned thereto in the Reseller Agreement.

           SECTION 2 Exhibit A - Authorized Territory of the Reseller Agreement
shall be deleted in its entirety and replaced with the following:

           The Reseller is granted the non-exclusive right to resell ORBCOMM
           Products and Services for Intelligent Transportation System
           monitoring, tracking and messaging applications to Federal, State
           and local Government and commercial accounts.  Excluded from this
           territory definition is the right to resell ORBCOMM Products and
           Services (a) for barge tracking and monitoring applications on the
           inland waters of the United States, and (b) to United States-based
           rail companies for the specific purposes of monitoring and/or
           tracking rail cars used exclusively for the transportation of
           automobiles and trucks, which rail cars are know as "Autorack
           Railcars".

           IN WITNESS WHEREOF, the parties have executed this Amendment No. 1
as of the day and year first above written.

                               ORBCOMM USA, L.P.

                                      By:
                                         -----------------------------
                                          Name: Xxxxxx X. Xxxxxx
                                          Title: President

                               ORBITAL SCIENCES CORPORATION ITS GROUP

                                      By:
                                         ------------------------------
                                          Name: Xxxx Xxxxx
                                          Title: Contracts Manager, ITS Group