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How do ground monitoring stations keep GPS satellite orbit information accurate?

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Cruise ship captain in uniform studies navigational charts with a compass on a table in the ship's bridge. — navigation Officers on a passenger ship using charts for navigation.

Ground monitoring stations maintain the accuracy of GPS satellite orbits through a coordinated process managed by the system's control segment.1

Four uncrewed monitoring stations located globally track all satellites within their view to detect orbital variations. These fluctuations are primarily caused by the gravitational influence of the Moon and Sun, the nonspherical shape of Earth, and the pressure exerted by solar radiation.1

Once these variations are identified, the data is processed at the Master Control Station. Corrected orbital information is then relayed back to the satellites using large ground antennas. Additionally, if satellites drift too far from their intended configuration over time, ground control commands them to fire onboard thrusters to nudge them back into their proper positions.1