GPS-2F (Global Positioning System) or Navstar-2F (Navigation System using Timing And Ranging) satellites are the fourth evolution stage of the second generation of the GPS satellites. Improvements included an extended design life of 12 years, faster processors with more memory, and a new civil signal on a third frequency.
The GPS-2F satellites do not need to carry an apogee kick motor, in contrast to the earlier generations, as the launch vehicles provide direct insertion into the GPS orbit. Originally the Delta-4M version was to be used for the Delta launches, but a mass growth of the satellites required a switch to the more powerful Delta-4M+(4,2) version. For Atlas launches, the Atlas-5(401) version is used.
Boeing was contracted with options for up to 33 Block-IIF satellites in 1996, but in 2001 the contract was reduced 12 Block-IIF satellites. In July 2006, satellites 10, 11 and 12 were contracted. The first Block-IIF satellite was originally scheduled to launch in 2006, but was finally launched in 2010. The final launch was in February 2016.
Also carried as a secondary payload were nuclear detonation detection sensors (NDS).
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