GPS Block IIF
Interim GPS satellites bridging to Block III, final Block II series.
GPS Block IIF is an interim class of GPS satellite that bridged the gap between earlier Navstar Global Positioning System generations and the GPS Block III satellites. Built by Boeing and operated by the United States Air Force, these spacecraft were launched by the United Launch Alliance using Evolved Expendable Launch Vehicles. They are the final component of the Block II GPS constellation to be launched, with the last satellite successfully launched on 5 February 2016, completing the series.
Quick Facts
- Names list
- GPS IIF
- Manufacturer
- Boeing
- Country
- United States
- Applications
- Satellite navigation
- Orbits
- Semi-synchronous MEO
- Operator
- United States Air Force
- Lifetime
- 12 years (planned)
- Preceded
- GPS Block IIR
Facts from the source article.
Lore & Background
The original contract for Block IIF, signed in 1996, called for 33 spacecraft, but this was later reduced to 12. Program delays and technical problems pushed the first launch from 2006 to 2010. Because the Evolved Expendable Launch Vehicles are more powerful than the Delta II used for earlier Block II satellites, they can place the satellites directly into their operational orbits, so Block IIF satellites do not carry apogee kick motors.
These satellites supplement and partially replace the GPS Block IIA satellites launched between 1990 and 1997, which had a design life of 7.5 years. The final Block IIA satellite was decommissioned on 9 October 2019. The operational constellation now includes Block IIR, IIRM, IIF and III variants.
New characteristics include broadcasting the L5 "safety of life" navigation signal (first demonstrated on USA-203), broadcasting a new M-code signal, doubling in predicted accuracy, better resistance to jamming, and reprogrammable processors that can receive software uploads. They are the first GPS satellites not to have Selective Availability hardware installed, which had degraded civilian accuracy when turned on in the original satellite fleet.
Reader's Guide
The GPS Block IIF satellites represent a transitional generation that introduced several key technical advances while maintaining compatibility with the existing GPS infrastructure. Their most notable contribution is the introduction of the L5 "safety of life" signal, which was first demonstrated on satellite USA-203 and is designed for aviation and other safety-critical applications. The addition of the M-code signal enhances military use with improved security and anti-jamming capabilities.
The doubling of predicted accuracy and better jamming resistance marked a significant improvement over earlier blocks. The reprogrammable processors allow for software updates after launch, enabling the satellites to adapt to evolving requirements without hardware changes. The removal of Selective Availability hardware was a permanent shift away from the intentional degradation of civilian signals that had been possible in earlier satellites.
Of the 12 GPS Block IIF satellites launched, 11 are currently operational. Their direct injection into operational orbits by more powerful launch vehicles eliminated the need for apogee kick motors, simplifying the spacecraft design. The series completed the Block II constellation, bridging the gap until GPS Block III satellites became operational, and their signals continue to form part of the modernized GPS architecture alongside Block IIR, IIRM, and III variants.
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