The Global Positioning System (GPS) is a space-based radio-navigation system that provides precise information on position, velocity, and time. GPS uses a constellation of satellites in orbit to transmit signals that a GPS receiver on the ground uses to calculate its position. Each satellite carries an atomic clock that broadcasts time information in the signals it sends. The satellites also carry a record of their own position and time. The receiver uses the time difference between when it receives a signal and when it was broadcast to calculate the distance from the satellite. The receiver can then use this information to calculate its own position.