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Comment by londons_explore | Hacker News Reader

I'm surprised there are quite so many single satellite outages, and no whole-system outages.

What causes satellites to suffer single satellite unplanned outages? Uploading bad software? Bad data? Wrong commands for orbit adjustment?

One would think that after the 20th time these mistakes had been made, automated tests would be in place to prevent them happening again.

Yet it's impressive no whole-network outage has happened. Presumably after uploading data/commands to one satellite, it gets uploaded to the rest. Yet there has never been a time that everything looked okay till after it was deployed worldwide?

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The majority of those outages are listed as single-minute, (or as planned downtime).

And there are 31 GPS satellites in orbit when global coverage is possible with only 24.

This, combined with a fully redundant control segment on the ground and a satellite 'autonav' feature that lets them run (with degraded accuracy) for up to 60 days without the control segment provides reasonably good protection against whole-system outages.

There's a bunch of maintenance stuff that happens regularly that's on that list... FCSTDV (stationkeepng burns), FCSTMX (scheduled maintenance, like switching to a different atomic clock or the like), that sort of thing.

There's a lot of recent UNUNOREF on the agi.com link in this thread's grandparent, which is basically "it broke and came back before we could send out a note". If you look closely at that list, though, you'll see that almost all of the recent events are a single satellite -- PRN18. I have no idea what's wrong with it (and AFAIK there's no way for the public to get the details), but it's been going unhealthy for ~2 minutes at a time for months now.

(I'm guessing they keep it live because either don't have another satellite positioned so they can put it into that slot easily, or because they don't consider whatever is wrong with it to be a huge problem.)

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