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GPS IIR/IIR-M


MISSION

Deliver sustained, reliable GPS capabilities to America's warfighters, our allies and civil users. GPS provides positioning, navigation and timing service to civil and military users worldwide.

BACKGROUND

In 1989, the GPS IIR contract was awarded to Lockheed Martin for the development and production of 21 space vehicles. In August 2000, the United States Air Force awarded Lockheed Martin a contract to modernize eight existing GPS IIR satellites. On Aug.17 2009, the last GPS IIR-M (modernized) satellite was launched from Cape Canaveral Air Force Station, Fla.

DESCRIPTION

The GPS IIR/IIR-M program has entered into the sustainment phase with closeout of the original GPS IIR contract pending.

· Current contract: Sustainment
Monitor GPS IIR satellites from Schriever Air Force Base
Support 2nd Space Operations Squadron in day-to-day control and maintenance
Provide trending analysis
Provide expertise in resolving anomalies/out-of-family conditions

· Production Contract: Closeout Contract Line Numbers
Disposition of all GPS IIR/IIR-M material
Verify and close remaining CLINs
Continue to execute the on-orbit incentive plan
Final contract actions

CAPABILITIES
· Legacy signals: L1 C/A, L1/2 P(Y)
· Modernized signals: L2C (GPS IIR-M only), L1/2 M-Code (GPS IIR-M only)

GENERAL CHARACTERISTICS
· Orbit: Six orbit planes at 55 degree inclination
· Altitude: 10,898 nautical miles
· Design life: 7.5 years, 6-years MMD
· On-orbit weight: 2484 lb
· Size: 62 in wide, 77 in deep, 87 in high
· Position accuracy: 3 meters, with daily updates from the control segment

Electrical Power Subsystem
· Solar array: 144 ft2; high-efficiency silicon cells, 1040-watt capacity
· Battery system: NiH2, rechargeable
· Electronics: Central controller with redundant discharge converters and battery chargers

Attitude Determination and Control
· Design approach: Zero momentum, 3-axis stabilized, Earth-oriented, Sun-nadir pointing
· Attitude reference control: Static Earth sensor, Sun sensor, reaction wheels/magnetic coils

Propulsion Subsystem
· Design approach: Monopropellant N2H4
· Propellant capacity: 208 lbs
· Thrusters: Twelve 0.2-lb REAs and four 5.0-lb REAs

Navigation Payload
·
Timekeeping subsystem: Multiple atomic frequency standards: Rubidium clocks, radiation-hardened design, high stability timing, automated integrity monitoring
· Mission Data Unit: 1750A central processor, ADA HOL, integral baseband processor, full message encoding and processing, real-time Kalman filter
· Crosslink transponder data: RF receive and transmit, precision inter-satellite ranging, full-frame modulation and mode control
· New IIR-M signals: M-Code (L1/2), Selectable C or C/A on L2

Structure and Thermal
·
Modular design: Six aluminum honeycomb panels mounted to a central aluminum core
· Passive thermal control: Blankets, thermal coatings, radiators, and electrically controlled heaters, new L-band panel with heat pipes for GPS IIR-M SVs

Tracking, Telemetry, and Command
·
RF links: Six S-band, SGLS transponder
· Security architecture: Encrypted data links, redundant 1750A control processor, centralized command decoding and telemetry communications
· Autonomy: On-board power and key component redundancy management

Prime Contractor: Lockheed Martin