US to turn off GPS if naughty people use it

I stumbled across this article which I wanted to comment on, but needed to log in. That's all far too tedious, so I'm writing here instead.

Apparently, the US wants supreme GPS control of the world (what a suprise). They reserve the right to switch off GPS if their enemies are using it against them. That sounds fair enough, after all, they put it up there and they maintain it. However, they also reserve the right to shoot down European GPS satellites if US enemies use them against the US. Hmm... now I'm not so happy.
We must remember the supreme stupidity of the US on this issue though. When GPS first started, they had something called Selective Availbility (SA) switched on. That meant that the civilian GPS channel had deliberate "noise" added, so one could only approximate one's position to around 10 metres (the military channel was of course unaffected).

Naturally, everyone working on GPS at the time spent enormous amounts of time and money working out ways to reduce the effect of SA. Indeed, some of the worlds most brilliant mathematicians and engineers worked out very clever ways to work around SA. One of the most effective means was by Differential GPS. A fixed point, which knew precisely where it was would simply broadcast the error it was experiencing due to SA. Any GPS receiver in the vacinity would simply subtract that error from what ever it was receiving and then would have it's position pretty precisely. There was even a plan to broadcast this information across the UK on Classic FM's RDS data. And so we see vast amounts of infrastructure being introduced to circumvent SA.

Around about this time, the US walked into Haiti. At that time, not many people were interested in military GPS systems, so the US army didn't have enough of them. Instead, they emptied the shelves at Walmart of all the civilian ones they could find. For the couple of weeks while "major combat operations" took place, they switched off SA. The rest of the world feverishly worked on analysing GPS signals so that they could work around SA when it came back on.

Sometime afterwards, the US realised that they should never have switched SA on in the first place. The world was becomming SA-imune. And thus, it was switched off.

Some anti-SA technology still exists in GPS receivers. The normal errors you get when receiving GPS signals are just like SA. Even a cheap GPS receiver will perform complex mathematical calculations to "smooth" out the errors and give you a (seemingly) precise location. Of course, real SA will swamp such calculations if it's ever re-introduced.

So the US wants to be able to control GPS capablities. I suppose you can't blame them, but remember, Europe wouldn't feel the need to have it's own GPS system if the US was more reliable with theirs. I suspect the US is not letting European forces use the military (SA free) GPS channels. It's precisely because the US wants to be able to stop/start GPS at will that Europe feels the need to have a system of it's own. So much for allies.

So we see the US behaving as it always does (and mimicked by it's corporations): "We have superiority. If you try to userp us, we will attack you." ("Peace through superior firepower"). So much for capitalist competition. No wonder some people have a problem with globalisation.

One bend in the road may be space-junk. If the US did ever shoot down European satellites, there would be an unprecidented amount of space-junk hurtling around in orbit. GPS satellites are in high earth orbit, so this would not likely affect things like the ISS, but would affect other GPS satellites. Given the US has a constellation of 26, what are the chances of one of them floating into a cloud of fast moving (uncontrollable, and unstoppable!) space-junk? (and don't forget - each GPS satellite contains two atomic clocks) Each one destroyed exaserbates the problem. Carefully placed European satellites could render US anti-satellite technology pointless - destroy one, destroy them all.

Submitted by coofercat on Thu, 2004-12-30 01:16



I agree with you wholeheartedly about the arrogance of American policy. But I think you overstate the (relative) danger of "space junk". There are already thousands of old satellites and things cluttering up the sky, so another couple of dozen wouldn't make the "unprecedented" impact you suggest.

I wonder what the posible legal repercussions would be if the US attacked European GPS satallites. You could certainly argue that a great many emergency services will be relying upon the system and that civilian lives would thus be endangered. However, the precedent set by the nuclear non-proliferation policy of both the United States AND Great Britain would make our state a hypocritical one at the very least if we objected to such a strike.

On top of that, you have Guantanamo Bay, the Iraq invasion, etc, showing that the US doesn't give a flying f--- about international law anyway.

Submitted by Greg (not verified) on Tue, 2006-10-10 10:19.
GPS switch off

One worrying aspect of this is the possible effects on emergency communication systems. I personally maintain a quasi-synch radio scheme where the transmitter frequencies are stabilised by comparison to the 1pps signal extracted from GPS receivers, the voice and data channels of this radio scheme are carried by VOIP on land lines and the audio phasing is also corrected utilising GPS timing.

I can survive without my "Tom-Tom" in the car but many radio and cellphone operators need to produce a contingency solution before the GPS network goes offline, word from reliable sources is that it WILL be switched off very soon, I have no idea of the duration of the switch off.

Sadly I was always cynical about DEPENDING on GPS, for the above applications a useful amount of stability is obtainable from conventional ceasium reference oscillators.

Submitted by g0fvt (not verified) on Thu, 2007-11-15 13:25.