The GPS system is divided into three segments:
The Space Segment
GPS uses twenty-one operational satellites, with an additional three satellites in orbit as redundant backup.
GPS uses NAVSTAR satellites manufactured by Rockwell International. Each NAVSTAR satellite is approximately 5 meters wide (with solar panels extended) and weighs approximately 900Kg.
GPS satellites orbit the earth at an altitude of approximately 20,200Km.
Each GPS satellite has an orbital period of 11 hours and 58 minutes. This means that each GPS satellite orbits the Earth twice each day.
These twenty-four satellites orbit in six orbital planes, or paths. This means that four GPS satellites operate in each orbital plane.
Each of these six orbital planes is spaced sixty degrees apart. All of these orbital planes are inclined fifty-five degrees from the Equator.
The Control Segment
The Master Control Station (MCS) of the GPS system is operated at Schriever Air Force Base in Colorado Springs, Colorado. The United States Air Force maintains redundant Master Control Stations in Rockville, Maryland and Sunnyvale, California.
The Air Force also maintains monitoring stations in Colorado Springs, Hawaii, The Ascension Islands, Diego Garcia, and Kwajalein.
Communications with the space segment are conducted through ground antennas in the Ascension Islands, Diego Garcia, and Kwajalein.
The User Segment
The GPS user segment is any person with a GPS receiver.
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