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Global Positioning System

GPS History
Originally established by the Department of Defense, the global positioning system (GPS) is a satellite navigation system. It consists of approximately 24 satellites in orbit around the Earth, several ground tracking stations, and a receiver in the aircraft, other vehicle, or held by an individual. The ground control sites watch where the satellites are in orbit and continually correct their reported location and time-of-day signals. This is done so that when the satellite communicates with a receiver, it gives the best possible position it can to help navigate.

The GPS receiver converts the signals coming from the satellites into position coordinates. It can give a pilot his latitude, longitude, elevation, and current time as long as the receiver can "see" any four of the 24 satellites.

Position accuracy is very important to military operations. As of the year 2000, GPS signals are encoded so that only U.S. military forces can use it. This is called the Precise Positioning System (PPS). So that the civilian community can also use GPS, the GPS satellites send out an additional signal for position data that is accessible by non-military users. This is called the Standard Positioning System (SPS).

Global Positioning System
Global Positioning System