##### 



Exhibit 10.5.1
 
 
      Additional Payload #3:
    
    October 4, 2007Additional Payload (& antenna) #4:
    
    October 11, 2007 (also includes antenna for PL #3)Additional Payload (& antenna) #5:
    
    October 21, 2007Additional Payload (& antenna) #6:
    
    The date that is 75 days from the receipt by Orbital of the payload plate.
    Orbital Sciences Corporation  Space Systems Group  21839 Atlantic Blvd., Dulles, VA 20166  703-948-8300




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##### 



ORBCOMM INC.
    
    
    
    ORBITAL SCIENCES CORPORATIONBy:
    
    /s/ John J. Stolte
    
    
    
    By:
    
    /s/ Rob Cramer
 Name:
    
    John J. Stolte
    
    
    
    Name:
    
    Rob CramerTitle:
    
    EVP TECH & OPS
    
    
    
    Title:
    
    Director of ContractsDate:
    
    10/15/07
    
    
    
    Date:
    
    10/16/07
 Orbital Sciences Corporation  Space Systems Group  21839 Atlantic Blvd., Dulles, VA 20166  703-948-8300




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##### 



ITEM
    
    DESCRIPTION
    
    PART NUMER
    
    QTY.#1
    
    EGSE PAYLOAD RACK A ASSEMBLY
    
    S15872030000-01
    
    
    12
    
    GPS RECEIVER  SYMMETRICOM
    
    XL-AK
    
    
    13
    
    PRECISION C/N GENERATOR  NOISE/COM
    
    UFX-BER-IF1
    
    
    14
    
    FREQUENCY COUNTER  FLUKE
    
    PM6685
    
    
    15
    
    POWER METER  AGILENT
    
    E4418B
    
    
    16
    
    POWER HEAD  AGILENT
    
    E9301H
    
    
    17
    
    SPECTRUM ANALYZER  HP/AGILENT
    
    8560B
    
    
    18
    
    SIGNAL GENERATOR  AGILENT
    
    E4434B
    
    
    19
    
    SIGNAL GENERATOR  AGILENT
    
    E4438C
    
    
    110
    
    ACE-360 COMM INTERFACE  ORBITAL
    
    4AA80000132-01
    
    
    111
    
    VME RACK MOUNT CHASSIS  SYNERGY
    
    N/A
    
    
    112
    
    TORREY MODEM CARD  TORREY SCIENCE
    
    N/A
    
    
    113
    
    DSP CARD  SYNERGY
    
    DSP-440
    
    
    114
    
    VTI CARD 48V  SYNERGY
    
    N/A
    
    
    115
    
    POWER SUPPLY CHASSIS  AGILENT
    
    N6700B
    
    
    116
    
    POWER SUPPLY CHASSIS  AGILENT
    
    N6700B
    
    
    117
    
    POWER SUPPLY CHASSIS  AGILENT
    
    N6700B
    
    
    118
    
    POWER MODULE 0-20V  AGILENT
    
    N6743B
    
    
    119
    
    POWER MODULE 0-20V 15A  AGILENT
    
    N6773A
    
    
    120
    
    POWER MODULE 0-8V  AGILENT
    
    N6732B
    
    
    121
    
    PAYLOAD MONITOR PANEL  ORBITAL
    
    S15872030100-01
    
    
    122
    
    EGSE PAYLOAD RACK B ASSEMBLY
    
    S15872030000-01
    
    
    123
    
    SIGNAL GENERATOR  HP/AGILENT
    
    8643A
    
    
    124
    
    RF SWITCH MATRIX  ORBITAL
    
    S158720303Y0-01
    
    
    125
    
    ANTENNA SIMULATOR  ORBITAL
    
    S158720304Y0-01
    
    
    126
    
    RF MONITOR PANEL  ORBITAL
    
    S15872030200-01
    
    
    127
    
    Sun Workstation w/pasissim and atlas card software
    
    TBD
    
    
    128
    
    Sun Keyboard
    
    TBD
    
    
    1
 Orbital Sciences Corporation  Space Systems Group  21839 Atlantic Blvd., Dulles, VA 20166  703-948-8300




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##### 



29
    
    Sun Mouse
    
    TBD
    
    
    130
    
    Sun Monitor
    
    TBD
    
    
    131
    
    Desktop PC w/Labview license and Orbital Labview software
    
    TBD
    
    
    132
    
    PC Keyboard
    
    TBD
    
    
    133
    
    PC Mouse
    
    TBD
    
    
    134
    
    PC Monitor
    
    TBD
    
    
    135
    
    PAYLOAD EXTERNAL POWER INTERFACE CABLE
    
    S15872036200-01
    
    
    136
    
    PAYLOAD EXTERNAL DATA INTERFACE CABLE
    
    S15872036000-01
    
    
    137
    
    [Removed]38
    
    RF TEST PORT CABLES
    
    TBD
    
    
    3
 Orbital Sciences Corporation  Space Systems Group  21839 Atlantic Blvd., Dulles, VA 20166  703-948-8300