[outworlder]

The most interesting part of the whole write up is that it sheds light on how dependent of the base stations these constellations are. I used to think that, other than sending orbital corrections and the occasional fixes, the constellation would run itself. Apparently this is not the case.

So a localized outage can in fact affect the entire planet. This has also implications in disaster scenarios.

Not sure how applicable this is for GPS.

[nwallin]

The GPS constellation is considerably more robust to a ground station outage. If the ground station goes out, the satellites themselves are a distributed network and they use each others' data to correct themselves. It can operate in this mode for something like 60 days before it's unable to continue correcting itself.

Of course, if the ground station failure was a soft failure, and instead of ceasing to upload, it began uploading incorrect data, the GPS location results would be arbitrarily bad to unusable. It's not clear to me whether the Galileo outage was because of a hard ground station failure or a soft one. But given that one of the contributing factors was that the backup system was not online, it would indicate to me that this was a hard failure that GPS would have been able to correct.

[bradknowles]

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....

[walrus01]

This is one of the reasons for the ridiculously high perimeter security around Schriever AFB in Colorado, which runs the GPS network, and a number of other critical DoD satellite programs. It's guarded as thoroughly as the Pantex plant in Texas.