Global Positioning System (GPS)

The United States Global Positioning System (GPS) is a satellite-based system used for navigation, position determination, and time-transfer applications, that meets the ICAO Global Navigation Satellite System (GNSS) requirements. The system consists of a 24-satellite constellation plus associated ground-based monitoring and control facilities; it is operated and maintained by the Department of Defense. The satellites radiate precisely timed signals coded so that a receiver on or near the surface of the earth can determine both the transmission time delay (or equivalently, distance) from the satellite to the receiver and the precise satellite position. By simultaneously receiving such signals from at least four satellites, the receiver can determine its position and time.
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GLONASS is a Russian satellite navigation system similar to GPS. GLONASS status information is originally provided by the University of Leeds, Institute of Electronic and Electrical Engineering, UK - the Coordinational Scientific Information Center CSIC (Moscow), Russian Space Forces, Ministry of Defense - and the Intergovernmental Navigation and Information Center (INIC, Moscow).

GPS Documents may be downloaded on the ICASC's Documents for Downloading page.