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GPS Block II F

The Block IIF satellite, the latest generation of GPS vehicles that are planned to begin replacing older satellites in 2001 and are managed by the NAVSTAR GPS Joint Program Office. Boeing North American Space Systems Division is the prime contractor for the Block IIF, which incorporates current technology to sustain the GPS utility for military and commercial use.

The NAVSTAR Global Positioning System (GPS) Joint Program Office procurement of the NAVSTAR Global Positioning System Sustainment (Block IIF) will sustain the quality GPS signal as a worldwide utility well into the next century at the lowest technical risk and acquisition and life-cycle costs. Under a single contract, the system level prime contractor is responsible for consolidating the satellite and operational control subsystems into one optimized package, and integrating this package with a government furnished launch vehicle, secondary payload(s), and the Air Force Satellite Control Network. GPS Block IIF does not include the acquisition or production of any user equipment. The contractor will deliver this Block IIF System to the Government, and Air Force Space Command will launch and operate the system on a daily basis. The system will be backward compatible with previous GPS satellite, control facilities, and user equipment.

The proposed procurement for a constellation of 51 GPS Block 2F series satellites has been reduced to 33 satellites.

The Block IIF system allows affordable technology insertion and block upgrades, while emphasizing compatibility and interoperability with the current space vehicles, ground control system, and user equipment. The system will interface with the new GPS Operational Control System (OCS) architecture currently under development, and with the Air Force Satellite Control Network (AFSCN).

Air Force will use the Evolved Expendable Launch Vehicle (EELV) as the booster.

The requirement to maintain a worldwide navigation service provided by a 24 satellite constellation for military and civilian users drives the Block IIF program.

The Block IIF spacecraft will feature advanced atomic clocks to greatly improve performance and give the control segment greater visibility into the health of the units. With four frequency standards composed of both cesium and rubidium technologies, these extremely accurate GPS atomic clocks must keep time to within 8 nanoseconds a day.

The improvement involves converting the GPS cesium clocks from analog to digital the first ever use of the commercially available digital cesium standard technology on spacecraft and are a result of long-standing development work on frequency standard technologies by the U.S. Naval Research Laboratory in Washington, D.C.

The processor-controlled cesium clocks continuously optimize their performance by adjusting internal parameters and compensating for environmental effects. They will also perform self-checkout diagnostics. The current analog clocks are optimized during manufacturing. As components age, the clock performance becomes less predictable and the output frequency of the clocks varies with changes in temperature or the magnetic field. The digital cesium standard represents the next step in the evolution of frequency standards in space and promises to result in better accuracy for military and civilian GPS users alike.

The market for atomic clocks is shrinking as GPS replaces atomic clocks in a number of their former applications. To preserve the industrial base and advance clock technology, the JPO, through NRL, funds development of new clock technologies.


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Implemented by Charles P. Vick, Sara D. Berman, and
Christina Lindborg, 1997 Scoville Fellow
Maintained by Robert Sherman
Originally created by John Pike
Updated Thursday, June 05, 1997 8:54:42 AM