The Global Positioning System (GPS) satellite network is operated by the U.S. Air Force to provide highly accurate navigation information to military forces around the world. The network is also being used by a growing number of commercial products. 

The GPS space segment consists of into six orbital planes, requiring a minimum of four satellites in each, to operate. The GPS control segment consists of five monitoring stations (Hawaii, Kwajalein, Ascension Island, Diego Garcia, Colorado Springs), three ground antennas, (Ascension Island, Diego Garcia, Kwajalein), and a Master Control station located at Schriever AFB in Colorado. The NAVSTAR Global Positioning System is managed by the NAVSTAR GPS Joint Program Office at the Space and Missile Systems Center, Los Angeles Air Force Base, California.

Table 1: GPS Satellite Planes/Slots

The idea for a global positioning/navigation system was first proposed in 1940. There are four generations of the GPS satellite: the Block I, Block II/IIA, Block IIR and Block IIF. Block I satellites were used to test the principles of the system, and lessons learned from those 11 satellites were incorporated into later blocks. Block II and IIA satellites make up the current constellation. The third generation Block IIR satellites are currently being deployed as the Block II/IIA satellites reach their end-of-life and are retired. Block IIF satellites will be the fourth generation of satellites and will be used for operations and maintenance (O&M) replenishment.