GPS-2R (Global Positioning System) or Navstar-2R (Navigation System using Timing And Ranging) are the third evolution stage of the second generation of the GPS satellites.

The GPS-IIR replenishment satellites are produced by General Electric Astrospace (later Martin Marietta and Lockheed Missiles & Space) under a contract issued in 1989, which included 21 satellites based on the commercial AS-4000 bus. These provided improved navigation accuracy and longer autonomous satellite operation than earlier model GPS satellites. The satellites were three-axis stabilized and operated at downlink frequencies of 1572.42 MHz and 1227.6 MHz (L-Band) and 2227.5 MHz (S-Band). Lockheed was responsible for launch and flight operations support of the GPS-IIR through 2006.

Block IIR satellites provided dramatic improvements over previous blocks. They could determine their own position by performing inter-satellite ranging with other IIR vehicles. They also had reprogramable satellite processors enabling problem fixes and upgrades in flight, increased satellite autonomy, and radiation hardness.

The Air Force Research Laboratory (AFRL) is building and demonstrating a new class of low-cost satellites – referred to as “micro-satellites” – weighing less than 100 kilograms. These new satellites are being flown under the XSS (Experimental Small Satellite) Microsatellite Demonstration Project. In conjunction with the Air Force Space Command, Air Force Space and Missiles Systems Center, the Naval Research Laboratory, and industry, missions are underway to actively evaluate future applications of micro-satellite technologies to include: inspection; rendezvous and docking; repositioning; and techniques for closein proximity maneuvering around on orbit assets.

XSS-10 (Experimental Small Satellite 10), a 28 kilogram microsatellite, was launched as a secondary payload aboard a Delta-7925 launch vehicle carrying a Global Positioning Satellite (GPS) satellite. This mission demonstrated the complex interactions of line-of-sight guidance with basic inertial maneuvering. It was launched on January, 29. 2003.