Finding the repeat times of the GPS constellation

Single-epoch estimates of position using GPS are improved by removing multipath signals, which repeat when the GPS constellation does. We present two programs for finding this repeat time, one using the orbital period and the other the topocentric positions of the satellites. Both methods show that the repeat time is variable across the constellation, at the few-second level for most satellites, but with a few showing much different values. The repeat time for topocentric positions, which we term the aspect repeat time, averages 247 s less than a day, with fluctuations through the day that may be as much as 2.5 s at high latitudes.