Global Positioning System (GPS)

A navigation system that receives and processes signals from several satellites in geostationary orbit. A GPS device analyzes the time taken for a signal to arrive from a satellite whose precise coordinates are known and compares data from several measurements to calculate its own position on Earth. For the system to cover the entire surface of the planet, 24 navigation satellites are required; however, for improved accuracy and reliability, there are currently 31 such spacecraft in the GPS constellation.