GPS - Space Segment
The space segment includes the satellites and the Delta rockets that launch the satellites from Cape Canaveral, in Florida. GPS satellites fly in circular orbits at an altitude of 10,900 nautical miles (20,200 km) and with a period of 12 hours. The orbits are tilted to the earth's equator by 55 degrees to ensure coverage of polar regions. Powered by solar cells, the satellites continuously orient themselves to point their solar panels toward the sun and their antenna toward the earth. Each of the 24 satellites, positioned in 6 orbital planes, circles the earth twice a day.
The satellites are composed of:
Solar Panels. Each satellite is equipped with solar array panels. These panels capture energy from the sun, which provides power for the satellite throughout its life.
External components such as antennas. The exterior of the GPS satellite has a variety of antennas. The signals generated by the radio transmitter are sent to GPS receivers via the L-band antennas. Another component is the radio transmitter, which generates the signal. Each of the 24 satellites transmits it's own unique code in the signal.
Internal components such as atomic clocks and radio transmitters. Each satellite contains four atomic clocks. These clocks are accurate to at least a billionth of a second or a nanosecond. An atomic clock inaccuracy of 1/100th of a second would translate into a measurement (or ranging) error of 1,860 miles to the GPS receiver.