Explain the GPS control system and what it consists of.

• A. A network of ground based monitoring and control stations including 5 monitoring stations, 3 ground antennas, and 1 master station
• B. A network of satellites and on-board receivers only
• C. A set of airborne beacons and ground repeaters
• D. An entirely autonomous satellite system

Answer: (A)

The GPS control system is the ground-based portion that maintains the satellites and the navigation data they broadcast. It consists of three main elements: a master control station, multiple monitor stations, and ground antennas. The master control station is the central processor that analyzes observations from the monitor stations, calculates the precise satellite ephemerides (orbital data) and clock corrections, and prepares updates that are uploaded to the satellites. The monitor stations around the world continuously track the satellites, collect ranging data, monitor satellite health, and relay that information to the master control station. The ground antennas are the uplink/downlink sites used to communicate with the satellites, transferring the updated navigation messages and corrections to the space segment.

The typical configuration includes five monitor stations, three ground antennas, and one master station, which together form the control segment that keeps the GPS constellation accurate and reliable for users on the ground. This ground-based system is what distinguishes GPS control from just the satellites and user receivers; it provides the ongoing maintenance, data updates, and health monitoring that the satellites and users depend on.