Euro space agency's Galileo satellites stricken by mystery clock failures Europe's GPS-alike system Galileo is suffering a number of unexplained clock failures on its satellites, the European Space Agency has admitted. Each of the 18 Galileo satellites currently in orbit carries four maser*-based atomic clocks. Two clocks are hydrogen-based, while the other pair use rubidium. The ESA says the clocks …
"Could a hamster-powered reaction wheel work in microgravity?"
Yes of course, you just strap the hamster in, which is the same way astronauts use the treadmill on ISS. Unfortunately the poor bugger won't be unable to unstrap himself for a bit of R&R after a hard day and couldn't be trusted to strap himself back in again independently either. So you'd need a hamster with a bit of longevity in it and preferably a backup hamster too.
The usual acronym for a generic satellite positioning service is GNSS (global navigation satellite system). The one provided by the US Navstar satellites is called GPS. Yes, it is a Global Positioning System and the acronym would do perfectly well as a catch-all term, but is has become so strongly associated with the US Navstar system (like Hoover with Vacuum cleaners) that GPS on its own is usually taken to mean the US one.
[The term "GPS"] has become so strongly associated with the US Navstar system (like Hoover with Vacuum cleaners) that GPS on its own is usually taken to mean the US one.
No, actually, what you're saying is the exact opposite. You are arguing that the generic term "GPS" has come to be used to refer specifically to the US Navstar system, which would be like the generic term "vacuum cleaner" coming to be used to refer specifically to devices made by e.g. Hoover.
If people were starting to use the specific term "Navstar" when talking about just any GPS system then your analogy would be correct, but that's not what's happening.
"I think you will find that Joe Public has never heard of GNSS, and whilst he probably thinks the US are the only providers, he doesn't actually care as long as his smartphone can tell him where the nearest pub is."
That same Joe Public probably doesn't have a smartphone. He has an IPhone. He may have bought it from Samsung or some other vendor, but it's still his iPhone, And GPS is that device he sticks on the dashboard to tell him where to drive (or an app on the phone) Either way, he probably doesn't ever think about how it works and may have heard the word "satellite" at some point in his life.
But thumbs up for using all available tech to find the pub!
Actually this is a good point.
I think that a lot of systems might lock onto about what, 8? sources. But lets assume it only tracks perhaps 5.
How many of those 5 could be wrong, and how far off would the offset be?.
I am fairly sure data is regularly thrown out anyhow because it doesn't fit the standard of the other averages, it would still be interesting to know what type of issues it could cause.
I suspect that's incorrect and each needs at least three to be considered reliable enough to use.
With one the satellite has no idea in isolation if it's right or not, so it shouldn't offer its services for a fix. With three, if two agree and one does not it can be sure that the two are correct.
Hence four per sat, providing a redundant spare.
If I'm right, this is a real "brown trousers" problem for the ESA.
"
Indeed, both are GPS, but only one of them has reliable clocks.... the other will put punters off by 100's of km if this is not fixed.
"
Only if the clock does not keep accurate time. However in this case the issue is that the clocks are completely failing. If all clocks fail the punters will get no position at all. If some clocks remain working, the punters will get accurate positions. The nature of the clocks is such that they are likely to either be accurate or not work at all. Thus inaccurate position fixes (which is far worse than no fix at all) is not likely to occur.
A clock that keeps inaccurate time is failed as far as its purpose goes, so it would probably be disabled and considered 'failed' at that point. That's easy to tell via 'majority rules' until you get down to two working clocks.
Even then perhaps there is some sort of signal being sent from the ground to the satellites which provides a time reference sufficiently accurate for it to tell when one of the two working clocks is no longer keeping accurate time and must be 'failed'.
I don't know the circumstances of these particular failures, and what mechanism would exist for an atomic clock to run slow or fast, but I have to think they've built in something to detect that and 'fail' any clocks that cease to maintain accurate time for obvious reasons.
Speaking of 3rd clocks (for avoiding indeterminacy when both of your clocks are telling different time) and assuming you're referencing the 3rd man:
http://www.imdb.com/title/tt0041959/faq#.2.1.4
TL;DR: no, the Swiss didn't invent cuckoo clocks
(Galileo, Galileo, Bee-el-zi-bug's got a daemon set aside for me)
Sort of.
Each GPS satellite downloads an "almanac" of data that accelerates the process of finding other satellites. These include the orbital elements of those satellite. These drift slightly over quite a short period of time. That is why they have to be updated.
Sort of.
Each GPS satellite downloads an "almanac" of data that accelerates the process of finding other satellites. These include the orbital elements of those satellite. These drift slightly over quite a short period of time. That is why they have to be updated.
Being pedantic: the satellite broadcasts the almanac. It's the GPS receivers that download it.
Galileo's clocks were probably designed to be redundant. A small number of failures were expected. So if one fails you have a backup. Even if there's a design or manufacturing flaw affecting all the clocks of one type then you still have 2 clocks of the other type.
This is because the cost of launching a satellite is so high, and it takes so long, so it's cheaper and better to have redundant systems in place.
However, if clocks of *both* types are failing at a much higher rate than expected, that's a serious problem.
Comes to that, why not just learn to read a flippin' map?
The UK's OS maps are (or were, in '84 when I last bought one) elegant and eminently fit-for-purpose. Wish we had the same kind of maps in the USA.
>The UK's OS maps are (or were, in '84 when I last bought one) elegant and eminently fit-for-purpose. Wish we had the same kind of maps in the USA.
Well it's your own fault, if you insist on having a tantrum and storming out then you don't get to have nice things.
If you wish to invite the Ordnance Survey to tramp over your land armed with theodolites, marmite sandwiches and maps in little plastic cases around their necks then I'm sure they will be happy to do so.
"Well it's your own fault, if you insist on having a tantrum and storming out then you don't get to have nice things."
Eh? I'm an ex-pat but I didn't "storm off" anywhere.
[VOICEMODE=DALEK_RING_MODULATOR] Explain! Explain! [/VOICEMODE]
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