GPS 'close to breakdown'

[Chris N]

         GPS system 'close to breakdown' |
            Technology |
            guardian.co.uk
   

Does seem unlikely that the US government will let it fail, but it might provide an opening for Galileo.

[Charlotte]

That's a bit scary.  From ambulances failing to get to blue-light calls, to bombs coming down in the wrong place in Afghanistan.

Surely they're on it?

[Really Ancien]

Oh good, I've always wanted a sextant and I need an excuse.

Damon.

[Chris S]

It's rather a shame, in this "Global Village" we're supposed to be living in, that Europe had to "rival" the US system.

I'm sure it would have been better if it had been a true international effort between all major powers, working together for the general good. Still too tribal and military for that I guess. Pity.

[simonp]

*Failing to get excited by a possible loss of some position accuracy*

[nuttycyclist]

Although I now run GPS and like the ease of use, the reliance on somebody else maintaining the satellites was one of the reasons why I was so late in taking it up, and also why I maintain my map reading skills.

[border-rider]

There's not a chance they'll let this fail whilst the US military still needs it.

Even Iridium is still up there, now funded by certain US agencies.

They seem to have cocked up on the support & maintenance front, but I don't doubt that asses will be kicked and heads rolled now it's in the public domain.  Which might have been the point.

[Greenbank]

It'll never go completely. The market for GPS devices is simply too big for it to just collapse (as the media put it).

Even if it drops to 50m accuracy (from about 5m at best now) it'll still be perfectly usable, although the devices with badly written firmware will suffer (and so will their owners).

I still carry a routesheet holder and pages from a 1:250,000 road atlas in my bag, and I'm quite happy to use either/both to get me round any route. There's always been the possibility that my GPS unit will just suddenly randomly fail on me.

[TimC]

This was a story a year or more ago, when the US Air Force's GPS satellite replacement program [sic] was in tatters, and Gallileo looked like falling apart. Both programmes are now more or less back on track, and GPS looks safe for a good while yet. I've no doubt the story was floated just to keep one or two parties on their toes, but I think the crisis suggested by the story is long past.

[frankly frankie]

the reliance on somebody else maintaining the satellites was one of the reasons why I was so late in taking it up

Its just infrastucture.  You might as well be concerned that someone else maintains the roads you ride on, or generates the electricity you use to boil your kettle.

[Chris S]

Its just infrastucture.  You might as well be concerned that someone else maintains the roads you ride on, or generates the electricity you use to boil your kettle.

From my perspective, nobody is currently maintaining the roads we ride on  .

[andygates]

It's no closer to breakdown than we are close to blackouts and Jesus is close to coming back.  IIRC, the constellation can work with a fair few satellites missing.  And modern GPSs are really good at finding plenty of birds, too, and getting a good position from a lot of shonky weak data. 

And all they need to do is launch more.  The problems aren't real ones, they're silly business-related ones (like hiring monkeys). 

[onb]

The thing thats always struck me about GPS is just whats wrong with the good old fashioned map and compass.

[Jaded]

Yup, absolutely. They are flawed, but can work well, as long as it isn't windy or wet.

[Greenbank]

The thing thats always struck me about GPS is just whats wrong with the good old fashioned map and compass.

Nothing.

But that's like saying "The thing that's always struck me about bicycles is just what's wrong with good old fashioned walking".

A GPS means I can put a fair bit of effort in before the ride, and the get the benefit of that effort during the ride by hardly having to think about navigation whilst moving. Simply look at the screen and follow what you've told it to tell you to do at that point.

Note that I don't let it do much thinking on its own. I don't have any mapping, and therefore don't rely on its non-existent auto-routing capabilities. When I get within 100m of a point I want it to tell me what to when I get to that point, that's it.

[TimO]

The GPS system is meant to have in-orbit spares, I think generally the idea was to have one spare per plane, of which there are six.  Normally you would have four operational satellites in each plane, so plus one spare, so that would be thirty satellites in orbit with twenty four operational.

As it is, they actually have thirty one in orbit and operational.  They've modified the orbits somewhat, so that more than twelve are likely to be visible at any one time, and if your receiver is capable of tracking that many satellites simultaneously it can use them to improve the accuracy.

If they lost a satellite, they would probably just respace the remaining satellites in that orbital plane, which is relatively cheap to do (in fuel terms).

They also have a couple of functional, but retired satellites in orbit, which could probably be re-enabled if they were desperate.  The older satellites tended to use less accurate atomic clocks, so they would probably not provide as good a fix, but they would be better than nothing.

The story sounds a bit like scare-mongering, and you can't help wondering if it's been souped up a bit by the writer.

[simonp]

Galileo should not be tied into the GPS system because of the US govt's desire to interfere with the accuracy when it suits them (e.g. when fighting pointless wars).

So I'm quite glad that the EU have gone their own way.  There should be no reason why you can't build a receiver that can pick up both sets of signals anyway (and Galileo promises far greater accuracy than GPS as well).

[rogerzilla]

The recent satellites don't have the SA circuitry, so that option is dead.  The US military have other ways of denying an enemy access to GPS, though.

[TimO]

Yes, if I remember correctly, they've been developing receivers that don't use the C/A (Coarse/Acquisition) signal at all, and rely entirely upon the P (Precision) signal.  Since C/A is what commercial receivers use, I believe the intent would be to disable the C/A signal entirely or just jam it locally, so encrypted P-signal only receivers would work (actually that's an over simplification and the terms aren't quite right, but it's close enough).

Of course, the reason why they didn't use SA (Selective Availability) during the Gulf War was because they had to use a mass of commercial receivers since they didn't have enough military ones.  You wonder if a similar thing could happen in some future conflict if they couldn't get enough P-code only receivers.

[TimC]

There is and was a little more to it than that, but essentially you're correct Tim. In fact, the vast majority of military GPS receivers aren't P-code capable, and don't need to be and, as Roger said, the option of degrading the signal at the satellite is no longer available to the overall system. There are indeed other ways of denying service selectively. On top of that, the US Government is acutely aware of the commercial importance of GPS and is unwilling to risk the avalanche of writs that would come their way if they disabled the system (notwithstanding that all civilian users effectively use it at their own risk).

[andygates]

There is and was a little more to it than that, but essentially you're correct Tim. In fact, the vast majority of military GPS receivers aren't P-code capable, and don't need to be and, as Roger said, the option of degrading the signal at the satellite is no longer available to the overall system. There are indeed other ways of denying service selectively. On top of that, the US Government is acutely aware of the commercial importance of GPS and is unwilling to risk the avalanche of writs that would come their way if they disabled the system (notwithstanding that all civilian users effectively use it at their own risk).

Aye, it's trivially easy to set up local GPS jammers for commercial kit.  I believe such devices are in common use in t'Middle East.  GPS signals are so weak that all you need to do is overlay them with a little noise.

While the Gubmint could, theoretically, turn it off for everyone, they have shown restraint in doing this: basically, they do it once and the trust will fall out of the system.  So it's only folks who already have a deep investment in distrusting the US gov who really think this is likely. 

The rest of us know that a lot of gov, military and essential civilian services use the commerical signal.  I've heard tell of hiker's Garmins being used a lot where the mil kit isn't available.

GPS is an essential part of modern infrastructure, right up there with electricity and roads.  Where it's denied, it's denied very selectively. 

[frankly frankie]

There are indeed other ways of denying service selectively.

Fast-growing patches of rain forest?

[Jaded]

loose battery compartments...

[Bledlow]

I wonder when Glonass & Beidou receivers will be commercially available.

Really, we shouldn't call Navstar "GPS". All the other systems are also GPS.

[andygates]

Hoover. Google. Coke.

There are indeed other ways of denying service selectively.

Fast-growing patches of rain forest?

Visions of US troops mooching through Baghdad being followed by trees in Roomba-style robot flowerpots.

Triffids!