Global Positioning System

The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide geolocation and time information to a GPS receiver anywhere on or near the Earth where signal quality permits. It does not require the user to transmit any data, and operates independently of any telephone or Internet reception, though these technologies can enhance the usefulness of the GPS positioning information. It provides critical positioning capabilities to military, civil, and commercial users around the world. Although the United States government created, controls, and maintains GPS, it is freely accessible to anyone with a GPS receiver.

Overview

The GPS project was started by the U.S. Department of Defense in 1973. The prototype spacecraft was launched in 1978 and the full constellation of 24 satellites became operational in 1993. After Korean Air Lines Flight 007 was shot down when it mistakenly entered Soviet airspace, President Ronald Reagan determined that the GPS system would be made available for civilian use as of 1988; however, initially this civilian use was limited to an average accuracy of 100 meters (330 ft) by use of Selective Availability (SA), a deliberate error introduced into the GPS data for which military receivers could correct.

As civilian GPS usage grew, there was increasing pressure to remove this error. The SA system was temporarily disabled during the Gulf War, as a shortage of military GPS units meant that many US soldiers were using civilian GPS units sent from home.