Elements of GPS

GPS has three parts: the space segment, the user segment, and the control segment. The space segment consists of a constellation of 24 satellites plus some spares, each in its own orbit 11,000 nautical miles above Earth. The user segment consists of receivers, which you can hold in your hand or mount in a vehicle, like your car. The control segment consists of ground stations (five of them, located around the world) that make sure the satellites are working properly. The master control station at Schriever Air Force Base, near Colorado Springs, Colorado, runs the system.