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                                                                  EXHIBIT 10.5.2


                               AMENDMENT NO.2 TO
                      ORBCOMM SYSTEM PROCUREMENT AGREEMENT


         This Amendment No. 2 ("Amendment No. 2") to ORBCOMM System Procurement
Agreement is entered into this 24th day of March, 1997 between ORBCOMM Global,
L.P. ("ORBCOMM Global") and Orbital Sciences Corporation ("Orbital").

                                   WITNESSETH

         WHEREAS, the parties previously entered into ORBCOMM System
Procurement Agreement dated as of September 12, 1995 (the "Procurement
Agreement"); and

         WHEREAS, the parties with to amend certain terms and conditions
regarding the payment of certain milestones set forth therein;

         NOW THEREFORE, the parties agree as follows:

                            ARTICLE 1 - DEFINITIONS

         Terms used herein and not otherwise defined shall have the meanings
assigned thereto in the Procurement Agreement.

                             ARTICLE 2 - AMENDMENTS

         Section 2.1      The first sentence of Section 4.1(b) of the
Procurement Agreement shall be deleted in its entirety and replaced with the
following:

         Orbital shall invoice ORBCOMM Global on a monthly basis for a maximum
         of 90% of its costs incurred during such month plus, to the extent
         permitted by Section 4.1(f), such portion of the cost in excess of the
         maximum amount to be invoiced to ORBCOMM Global in accordance with
         such Section 4.1(f) and not previously invoiced and paid; provided
         however that Orbital shall not be entitled to invoice ORBCOMM Global
         under Section 4.1(a) and this Section 4.1(b) in a cumulative total
         amount greater than $125,884,929.

         Section 2.2      Section 4.1(c) of the Procurement Agreement shall be
deleted in its entirety and replaced with the following:

         The remaining 10% of costs incurred in any month through December 1997
         may be invoiced incrementally on completion of the Category B
         Milestone for that month as set forth in Exhibit B; provided however
         that Orbital shall not be entitled to invoice ORBCOMM Global under
         this Section 4.1(c) in an amount greater than $13,987,214.
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         Section 2.3      Section 4.1(e) of the Procurement Agreement shall be
deleted in its entirety and replaced with the following:

         The total amount paid under Section 4.1(a), (b) and (c) shall not
         exceed $139,872,143 (the "Total Costs").  In the event costs incurred
         through December 31, 1997, are less than the Total Costs, the parties
         shall negotiate additional Category B Milestones for payment of the
         remaining balance of the Total Costs.

         Section 2.4      Exhibit B to the Procurement Agreement shall be
deleted in its entirety and replaced with Exhibit B attached to this Amendment
No. 2.

                           SECTION 3 - MISCELLANEOUS

         Section 3.1      This Amendment No. 2 shall be construed in accordance
with and governed by the laws of the Commonwealth of Virginia, without giving
effect to the provisions, policies or principles thereof related to choice or
conflict of laws.

         Section 3.2      No changes to the Procurement Agreement are
authorized hereby except as otherwise specified in this Amendment No. 2.

         IN WITNESS WHEREOF, the parties have executed this Amendment No. 2 as
of the day and year first above written.


                                    ORBCOMM GLOBAL, L.P.
                                    
                                    
                                    By:                                        
                                       -------------------------
                                    Name:
                                    Title:
                                    
                                    
                                    
                                    ORBITAL SCIENCES CORPORATION
                                    
                                    
                                    By:                                        
                                       -------------------------
                                    Name:
                                    Title:






                                       2
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                                   EXHIBIT B

                        ORBCOMM PROGRAMMATIC MILESTONES

<TABLE>
<CAPTION>
         -----------------------------------------------------------------------------------------------------
         #                                        DESCRIPTION                                            DATE
         -----------------------------------------------------------------------------------------------------
         <S>   <C>                                                                                      <C>
         1     Determine FM1&2 antenna performance deficiencies                                         Sep-95
         -----------------------------------------------------------------------------------------------------
         2     Preliminary Launch Vehicle ICD Distributed                                               Oct-95
         -----------------------------------------------------------------------------------------------------
         3     Preliminary Electrical ICD Distributed                                                   Nov-95
         -----------------------------------------------------------------------------------------------------
         4     Avionics Box CDR                                                                         Dec-95
         -----------------------------------------------------------------------------------------------------
         5     Comm EDU (SRX,STX,G/W) Characterization Test                                             Jan-96
         -----------------------------------------------------------------------------------------------------
         6     EDU System Comprehensive Performance Test                                                Feb-96
         -----------------------------------------------------------------------------------------------------
         7     Electrical ICD Release                                                                   Mar-96
         -----------------------------------------------------------------------------------------------------
         8     EDU System Environmental Test Complete                                                   Apr-96
         -----------------------------------------------------------------------------------------------------
         9     Qual Unit Testing Complete on Structure, Avionics Box, BCR, SRX, STX, Gateway,           May-96
               and Antenna
         -----------------------------------------------------------------------------------------------------
         10    First Plane Flight Structures Delivered to OSC                                           Jun-96
         -----------------------------------------------------------------------------------------------------
         11    Preliminary Flight Checklist Released                                                    Jul-96
         -----------------------------------------------------------------------------------------------------
         12    Qual Vehicle Thermal Vacuum Test complete                                                Aug-96
         -----------------------------------------------------------------------------------------------------
         13    First 4 sets of Bus Flight units including Harness Ready for Integration                 Sep-96
         -----------------------------------------------------------------------------------------------------
         14    Acceptance Test - First Pegasus Motor Set                                                Oct-96
         -----------------------------------------------------------------------------------------------------
         15    HAPS Integration & Test Completed Successfully                                           Nov-96
         -----------------------------------------------------------------------------------------------------
         16    First Pegasus Launch - Separation from Pegasus Carrier Aircraft                          Dec-96
         -----------------------------------------------------------------------------------------------------
         17    First 8 sets of Flight STX, SRX, Gateway & Antenna units Ready for Integration           Jan-97
         -----------------------------------------------------------------------------------------------------
         18    24 sets of BCR, Avionics Box, SRX, STX & Gateway units Ready for Integration.            Feb-97
         -----------------------------------------------------------------------------------------------------
         19    12th spacecraft completes Integration and Test                                           Mar-97
         -----------------------------------------------------------------------------------------------------
         20    Plane 1 Preliminary Test Report Submitted                                                Apr-97
         -----------------------------------------------------------------------------------------------------
         21    First Pegasus Launch - Separation from Pegasus Carrier Aircraft.                         May-97
         -----------------------------------------------------------------------------------------------------
         22    Third Motor Set Flight Sim 1 Performed                                                   Jun-97
         -----------------------------------------------------------------------------------------------------
         23    20th spacecraft completes Integration and Test                                           Jul-97
         -----------------------------------------------------------------------------------------------------
         24    First Pegasus Launch - Separation from Pegasus Carrier Aircraft                          Aug-97
         -----------------------------------------------------------------------------------------------------
         25    26 sets of Solar Arrays complete                                                         Sep-97
         -----------------------------------------------------------------------------------------------------
         26    26 Structures complete preparation                                                       Oct-97
         -----------------------------------------------------------------------------------------------------
         27    Second HAPS completes Integration and Test                                               Nov-97
         -----------------------------------------------------------------------------------------------------
         28    26 Antenna Assemblies ready for Integration                                              Dec-97
         -----------------------------------------------------------------------------------------------------
</TABLE>
         Note : Milestones 16, 21 & 24 are identical and should be invoiced
         simultaneously upon First Pegasus Launch.  All milestones are 
         expected to be completed prior to the Third Pegasus Launch.