A Global Positioning System is a satellite-based navigation system that uses a network of 24 U.S. Department of Defense satellites orbiting the earth at about 12,000 miles. The system was originally designed for military purposes, but in the 1980's the system was made available for civilian use. The GPS satellites circle the earth twice a day in a very exact orbit. They transmit signals to GPS receivers that use the information to triangulate the user's precise location. These days GPS can be found in cars, boats, airplanes, construction equipment, and even laptop computers.
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