How do the Moon and Sun affect GPS satellite orbits?

The Moon and the Sun exert gravitational pulls that act as external forces on GPS satellites, causing variations in their orbits. These gravitational influences are classified as perturbations, which are deviations from the ideal elliptical motion a satellite would otherwise maintain.123

Because these gravitational forces can cause satellites to drift from their intended configurations over time, the GPS control segment must actively manage these effects. Monitoring stations track the satellites to detect these orbital changes, and the Master Control Station processes this data to calculate necessary corrections. These updates are then relayed to the satellites, which use onboard thrusters to nudge themselves back into their correct positions. This maintenance is essential for ensuring the accuracy and reliability of the global navigation system.1