The Global Positioning System is a constellation of orbiting satellites that provides navigation data to military and civilian users all over the world. The system is operated and controlled by the Air Force 50th Space Wing, located at Schriever Air Force Base, Colo.
GPS satellites, which weigh over 4,000 pounds each, orbit the earth every 12 hours, emitting continuous navigation signals. With the proper equipment, users can receive these signals to calculate time, location and velocity. The signals are so accurate, time can be figured to within a millionth of a second, velocity within a fraction of a mile per hour and location to within 100 feet. Receivers have been developed for use in aircraft, ships and land vehicles, as well as for hand carrying.
GPS provides 24-hour navigation services including:
- Extremely accurate, three-dimensional location information (latitude, longitude and altitude), velocity and precise time
- A worldwide common grid that is easily converted to any local grid
- Passive all-weather operations
- Continuous real-time information
- Support to an unlimited number of users and areas
- Support to civilian users at a slightly less accurate level
The GPS constellation is designed and operated as a 24-satellite system, consisting of six planes, with a minimum of four satellites per plane.
The GPS satellites are launched from Cape Canaveral, Fla. into nearly 11,000-mile circular orbits. While circling the earth, the systems transmit signals on two different L-band frequencies. Their design life is about 7.5 years.
The GPS Master Control Station, operated by the 50th Space Wing's 2nd Space Operations Squadron at Schriever AFB, Colo., is responsible for monitoring and controlling the GPS satellite constellation. The GPS-dedicated ground system consists of five monitor stations and four ground antennas located around the world. The monitor stations use GPS receivers to passively track the navigation signals on all satellites. Information from the monitor stations is then processed at the master control station and used to update the satellites' navigation messages.
The master control station crew sends updated navigation information to GPS satellites through ground antennas using an S-band signal. The ground antennas are also used to transmit commands to satellites and to receive state-of-health data (telemetry).
The GPS Joint Program office enhances many of the capabilities provided by the current satellite based position and navigation equipment. Applications such as mapping, aerial refueling and rendevous, geodetic surveys, and search and rescue operations will benefit from these enhancements.
Air Force Space Command's Space and Missile Systems Center at Los Angeles AFB, Calif., acts as the executive agent for the Department of Defense lead for acquiring GPS satellites and user equipment.
The USCG operates and maintains the Navigation Information Service for civilian GPS users; it can be reached at (703) 313-5900, 24 hours a day.
For more information on GPS, contact Air Force Space Command, Public Affairs Office; 150 Vandenberg, Suite 1105; Peterson AFB, Colo. 80914-4500; (719) 554-3731.
For information on the management of GPS, go to http://pnt.gov/ .
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