NAVSTAR (Navigation Satellite Time and Ranging)
A global positioning system (GPS), often referred to (particularly in the U.S.) as the GPS or NAVSTAR-GPS, which is based on a global system of 24 Department of Defense navigational satellites (21 operational plus 3 spares), completed in 1993 and designed to provide time, position, and velocity data for ships, planes, and land-based vehicles, and for many other purposes. The NAVSTAR satellites are arranged in six planes, each in a 12-hour, 20,000-km-high orbit. They transmit signals that allow the determination, to great accuracy, of the locations of special receivers. These receivers can be fixed on Earth, or in moving vehicles, aircraft, or in satellites in low Earth orbit. NAVSTAR is used in navigation, mapping, surveying, and other applications where precise positioning is necessary. Each satellite broadcasts two L-band (see frequency bands) radio signals containing ranging codes, ephemeris parameters, and Coordinated Universal Time (UTC) synchronization information. Both military and civilian users can use NAVSTAR-GPS receivers to receive, decode, and process the signals to gain 3-D position, velocity, and time information. Civilian receivers are somewhat less accurate than their military counterparts, owing to their inability to read the coded portions of the satellite transmissions.
The NAVSTAR system is managed by the NAVSTAR GPS Joint Program Office, located at Los Angeles Air Force Base. The civilian point of contact for NAVSTAR information is the U.S. Coast Guard's Navigation Center (NAVCEN). The NAVCEN provides system status information in the form of a document called a Notice Advisory to Navstar Users (NANU). Civil users have input to NAVSTAR system issues through the Civil GPS Service Interface Committee (CGSIC), which is organized by the Coast Guard.
The Russian counterpart of NAVSTAR is GLONASS.
Related entry GNSS
Related category SATELLITES AND SPACE PROBES
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