The other factor for the US GPS system is that there are actually over 24 ground stations, one for each time zone plus at least a couple of spares. A local fail

The other factor for the US GPS system is that there are actually over 24 ground stations, one for each time zone plus at least a couple of spares. A local failure in one time zone doesn’t take out the whole fleet — they can fall over to a backup ground station, and backups for the backups, etc....