The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System. Using a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system allows the receiver to GPS, to determine its location, speed/direction and time.
Developed by the Department of Defense, it was officially named NAVSTAR GPS (Contrary to popular belief, NAVSTAR is not an acronym, but simply a name given by Mr. John Walsh). Satellite group is managed by the U.S. Air Force 50th Space Wing. The cost of maintaining the system is about $ 750 million per year, including the replacement of aging satellites, and research and development. Despite these costs, GPS is free for civilian use as a public good.
GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, and scientific uses. GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks.