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The July Galileo Outage: What happened and why

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Re: The July Galileo Outage: What happened and why

#61

Post by makomk »

ahubert wrote: post #50
makomk wrote: post #12

Earlier quoted context omitted.

The 60 day long-term ephemerides were the older sytem. Autonav on the current GPS satellites is considerably fancier - basically, the satellites carry out ranging measurements between each other and compute their own updated clock and ephemeris solutions on the satellites themselves in a distributed fashion. Specced to provide essentially full accuracy for something like six months, minus ionosphere estimates which c…

Hi makomk, (author here) Indeed, Galileo has nothing like this. The GPS solution sounds exceptionally fancy, and it may go a long way to explaining where all those billions of USD/year go :-) Do you know if it has ever been tried for real? Thanks!

I'm not actually sure if it's been used for real, and I don't think it's really been needed - apparently it's rare for GPS ephemeris data uploads to be late by even an hour or two. In principle the idea is that it would be operating all the time and give slight accuracy and integrity monitoring improvements, but that doesn't seem to be a priority.

Incidentally, it seems like the EU is looking at developing their own version of Autonav for the next generation of Galileo, quite possibly with optical rather than radio links between the satellites.

Re: The July Galileo Outage: What happened and why

#62

Post by mistrial9 »

dzhiurgis wrote: post #21

Is 1cm accuracy part of Galileo system already operational? If so, why our phones and other devices cannot utilise it yet?

orbits in space are geometrically perfect, you can reasonably talk about 1cm accuracy there.. On earth, variations in a long list of things, including physically moving land (due to seismic activity), make "1cm accuracy" something that does not actually hold.. no doubt it has a lot of positive measuring ability .. but the real truth gets messy..

Re: The July Galileo Outage: What happened and why

#63

Post by bradknowles »

nwallin wrote: post #39
outworlder wrote: post #31

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 applic…

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 b…

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....
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