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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

#11

Post by vel0city »

toyg wrote: post #7
jtwaleson wrote: post #6

When was the last time GPS had issues like this? I can imagine that during the early years this happened there as well? Or maybe not, as military quality engineering requirements were stricter.

Or rather silence requirements were stricter. The military is not in the business of publicising failure and weaknesses.

This is a bit of the interesting aspect to this failure. Official channels have overall been pretty weak on details on what all happened in this error. Most public knowledge of what happened has been gleaned from the signals coming off the satellites themselves which anyone can see. This live data combined with understandings of how the system should work is most of the public knowledge of what has been going on.

I don't have a ton of knowledge into the deep technical aspects to GPS, but I imagine we would probably have some similar clues of an outage of this scale in GPS. Maybe a little less technical details of what is happening behind the scenes, but knowing a high percentage of satellites entering a no guarantee precision mode should be possible.

Re: The July Galileo Outage: What happened and why

#12

Post by makomk »

michaelt wrote: post #8
ahubert wrote: post #2

author here - if anyone has any questions or remarks, let me know!

I gather the US GPS system has "Autonav mode" where each satellite has long-term ephemerides, allowing 60 days of reduced-precision operation if the ground segment fails. Does Galileo have no such thing, or had the errors propagated into such data by the time someone sounded the alarm?

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 can only be measured from the ground.

As far as I can tell, Galileo has nothing like this. They have a small buffer of future ephemeris data, but the ground segment failure here was so long that it completely ran out. Their approach seems to be full accuracy or why even bother.

Re: The July Galileo Outage: What happened and why

#13

Post by michaelt »

9nGQluzmnq3M wrote: post #9
efm wrote: post #4

Earlier quoted context omitted.

Thanks for writing this. The title doesn't mention that Galileo is a Global Navigation System (GPS).

GPS refers specifically to the US system.

Unfortunately, anyone who knows what the acronym GNSS stands for probably also already knows Galileo is such a system. So changing the title to 'Galileo GNSS outage' probably wouldn't clarify matters :(

Re: The July Galileo Outage: What happened and why

#14

Post by cyanoacry »

ahubert wrote: post #2

author here - if anyone has any questions or remarks, let me know!

Nice article! I used to work in this space (was formerly in charge of GNSS hardware at my company), and it's neat to see Galileo being put through its paces.

I see now that the US gets to take GPS (and the fact that the Air Force pretty much runs it single-handedly) for granted. We are seeing _some_ problems (like the GPS III block upgrade and OCX, ahah), but the org chart seems to be considerably simpler than what Galileo's got to deal with.

Re: The July Galileo Outage: What happened and why

#16

Post by myself248 »

9nGQluzmnq3M wrote: post #9
efm wrote: post #4

Earlier quoted context omitted.

Thanks for writing this. The title doesn't mention that Galileo is a Global Navigation System (GPS).

GPS refers specifically to the US system.

Which is funny, because I've heard it both ways.

For a while, as new systems were coming online, GPS was being used as a generic term, and the US system was being referred to by its original name, NAVSTAR.

But only purists would do that, and everyone else kept saying GPS to refer to the US system, so the new term GNSS was invented as the generic.

I try to say NAVSTAR and GNSS to avoid the ambiguous GPS, just like I say "gridiron" and "soccer" to avoid "football".

Re: The July Galileo Outage: What happened and why

#17

Post by toomuchtodo »

makomk wrote: post #12
michaelt wrote: post #8

Earlier quoted context omitted.

I gather the US GPS system has "Autonav mode" where each satellite has long-term ephemerides, allowing 60 days of reduced-precision operation if the ground segment fails. Does Galileo have no such thing, or had the errors propagated into such data by the time someone sounded the alarm?

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…

Any chance we'll see WAAS reference stations with more autonomy for uploading ionsphere correction data directly to the constellation, instead of having to aggregate at master stations, which then forwards to ground uplinks?

Re: The July Galileo Outage: What happened and why

#18

Post by reaperducer »

myself248 wrote: post #16
9nGQluzmnq3M wrote: post #9

Earlier quoted context omitted.

GPS refers specifically to the US system.

Which is funny, because I've heard it both ways. For a while, as new systems were coming online, GPS was being used as a generic term, and the US system was being referred to by its original name, NAVSTAR. But only purists would do that, and everyone else kept saying GPS to refer to the US system, so the new term GNSS was invented as the generic. I try to say NAVSTAR and GNSS to avoid the ambiguous GPS, just like I s…

But only purists would do that

Perhaps the same sort of space nerds who still call Dish Network "Echostar."

/Waves hand.

Re: The July Galileo Outage: What happened and why

#19

Post by myself248 »

reaperducer wrote: post #18
myself248 wrote: post #16

Earlier quoted context omitted.

Which is funny, because I've heard it both ways. For a while, as new systems were coming online, GPS was being used as a generic term, and the US system was being referred to by its original name, NAVSTAR. But only purists would do that, and everyone else kept saying GPS to refer to the US system, so the new term GNSS was invented as the generic. I try to say NAVSTAR and GNSS to avoid the ambiguous GPS, just like I s…

But only purists would do that Perhaps the same sort of space nerds who still call Dish Network "Echostar." /Waves hand.

Or track the ISS as Zarya.

/waves a trusty Omnipoint phone

Re: The July Galileo Outage: What happened and why

#20

Post by marcosdumay »

michaelt wrote: post #13
9nGQluzmnq3M wrote: post #9

Earlier quoted context omitted.

GPS refers specifically to the US system.

Unfortunately, anyone who knows what the acronym GNSS stands for probably also already knows Galileo is such a system. So changing the title to 'Galileo GNSS outage' probably wouldn't clarify matters :(

"Galileo" can stand for a lot of things.
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