They are reset every time they pass over a ground station. But the drift rate due to SR and GR is substantially higher than the error in the clocks themselves, so they do make an excellent test-bed for Relativity.TheAntiRelative said:One other note of interest is that while the large GR effects are very pronounced and GPS would nearly immediately be off by a mile (no pun intended) if those considerations were not in the timing, the fact that the satellites are in elliptical orbits, combined with the random drift of the clocks themselves (3 us/day I think it was?)along and other small effects (sagnac and perhaps lense-thirring) requires that they be re-synchronized with earth clocks on a regular basis.
So while it is a beautiful GR test, I believe the level of error actually exceeds the kinematic effects over time and so it is not the best SR lab from what I hear.
Does anyone know how frequently they are reset? I thought I heard daily.