NAVSTAR Global Positioning System

NAVSTAR Global Positioning System (GPS)

The global positioning system (GPS) is based on a constellation of twenty-four satellites at 12,625 miles (20,200 km) above the earth in six orbits. Each of these satellites completes one orbit of the earth in 11 h and 58 min (i.e., two orbits in 23 h and 56 min). The acronym NAVSTAR stands for navigation by satellites and ranging. Any vehicle using the system must be equipped with a suitable receiver. The system uses time and ranging for determining precise navigational information. GPS signals are available at all points on the earth and provide 24-h navigation services, which include 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; and support to civilian users at a slightly less accurate level.