Global Positioning Satellite system
Developed, funded and controlled by the U.S. Department of Defense.
24 satellites orbit 11,000 miles above Earth, sending signals to civilian and military receivers below.
A receiver measures travel time of signal transmitted from each satellite and uses that data to calculate distance from that satellite. Receiver uses satellite positions as precise reference points to determine the location of a receiver.
Using that data from at least four satellites, a receiver can determine latitude, longitude, altitude, and time.
Refined technology has put GPS systems into cars, cell phones and even watches.
Basic GPS service provides users with approximately 100 meter accuracy 95 percent of the time anywhere on or near the surface of the Earth.
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