Global Positioning System (GPS) serves as a worldwide radio system and was originally developed and implemented by the U.S. Department of Defense. GPS is a satellite-based navigation system comprised of 24 orbiting satellites. GPS works on the principle that if you know an object's distance from several known locations, you can then calculate its location. The "known" locations are the GPS satellites, and the distance to the object is measured using the transit time of an encoded signal. The satellites also broadcast a data stream along with the encoded signal to transmit information about their location.