The knowledge of a satellite's orbit is taken by using the prior parameters of the orbit, predicting where the satellite will be, and pointing a combination of telescopes (for precise angular measurements) and radars (for precise distance measurements) at this location, and measuring the error between where the satellite is and where it is expected to be. A set of these observations are then used to update the "known" orbit.
This known orbit is then provided back to the satellite so that it can be broadcast. If this system of updates stopped working, the quality of GPS position estimates would degrade pretty quickly (think weeks, not years).
This also means that if a GPS satellite were to need to maneuver for some reason -- either periodically boosting back into its assigned orbit or for debris avoidance -- the normal system of updates will catch this and users will never have to know or care that the satellite moved.
This known orbit is then provided back to the satellite so that it can be broadcast. If this system of updates stopped working, the quality of GPS position estimates would degrade pretty quickly (think weeks, not years).
This also means that if a GPS satellite were to need to maneuver for some reason -- either periodically boosting back into its assigned orbit or for debris avoidance -- the normal system of updates will catch this and users will never have to know or care that the satellite moved.