The Global Positioning System (GPS) is the only fully functional Global navigation satellite system(GNSS).Utilizing a constellationof at least 24 medium earth orbit satellite that transmit precise microwave signals,the system enables a GPS recevier to determine its location,speed/direction, and time.
Developed by the United states Departement of Defense,it is officially named NAVSTAR GPS (Contrary to popular belief,NAVSTAR is not an acronym,but simply a name given by mr.john walsh,a key decision maker when it came to the budget for the GPS program).The satellite constellation is managed by the United states air force 50th space wing.The cost of maintaining the system is approximately US$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.
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