How GPS Works

The Global Positioning System consists of 24 Earth-orbiting satellites, called Navstars, that allow anyone with a GPS receiver to determine his or her longitude and latitude accurate to within 50 feet. Since the U.S. made it available for public use in the 1980s, the system has been used for everything from tracking freight trucks to helping hikers stay on course. Generally, eight satellites are “visible” to a GPS receiver at any time; the more signals a GPS receiver picks up the more accurate it is. In January 1999, the Clinton administration announced a $400-million initiative to add civilian signals to replacement GPS satellites scheduled for launch in the next decade.

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Researched by VICKI GALLAY / Los Angeles Times