Global Positioning System

The Global Positioning System is a satellite navigation system owned by the United States and operated by the Space Force. Its roots lie in 1960s programs such as the Navy's Transit system, which tracked ships using satellites, and the Department of Defense formally began the NAVSTAR GPS program in the early 1970s. The first satellite was launched in 1978, and the constellation of around two dozen satellites was complete in the mid-1990s. Each satellite broadcasts its position and a precise time signal from atomic clocks, and a receiver calculates its own location from the signals of at least four of them. Though built for the military, it was opened to civilian use and from 2000 the deliberate degradation of accuracy was switched off, leading to its use in phones, cars, aviation and surveying.

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