The Global Positioning System (GPS) is currently the only fully functional Global Navigation Satellite System. Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise radio signals, the system enables a GPS receiver to determine its location, speed and direction. GPS is free for civilian use as a public good and these days one can find GPS incorporated in watches, cars, digital maps etc.
People often wonder how much GPS functionality can be packed into a wristwatch form factor. There are so many questions which keep popping one's mind. Some think if it would really tell them where they were? Some wonder if they would be able to use the positioning data to get directions to their desired location. Would they be able to download maps and watch the progress? And of course then, how much would this thing cost?
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 precisetime reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks. It may be interesting to note that the cost of maintaining the GPS system is approximately US$750 million per year, including the replacement of aging satellites, and research and development. The satellite constellation is managed by the United States Air Force 50th Space Wing.
