What You Want To Know About GPS

GPS is a satellite-based radio navigation system developed and operated by the U.S. Department of Defense (DOD). GPS consists of three segments: space, control, and user.

The Space Segment consists of a minimum of 24 operational satellites in six circular orbits 20,200 km (10,900 NM) above the earth at an inclination angle of 55 degrees with a 12 hour period. The satellites are spaced in orbit so that at any time a minimum of 6 satellites will be in view to users anywhere in the world. These solar powered satellites continuously broadcast position and time data. There are currently 32 satellites to allow maintenance and repairs to be done while still maintaining the minimum 24 satellites in orbit.

The Control Segment consists of a master control station, with five monitor stations and three ground antennas located throughout the world. The monitor stations track all GPS satellites in view and collect ranging information from the satellite broadcasts. The monitor stations send the information they collect from each of the satellites back to the master control station, which computes extremely precise satellite orbits. The information is then formatted updated navigation messages for each satellite. The updated information is transmitted to each satellite via the ground antennas, which also transmit and receive satellite control and monitoring signals.