12.16.2004

So what logic defying plan is coming out of Washington today?


It seems like every day I am left scratching my head saying "What are they thinking?" Every single day something new is reported that I simply can't get my mind around.

Today we read that Bush has "ordered plans for temporarily disabling the U.S. network of global positioning satellites during a national crisis to prevent terrorists from using the navigational technology."

Supposedly this will only happen within "the most remarkable circumstances" and will only affect a certain area where the terrorist act is happening at the time.

The question on my mind is, how would they do it? Why would they want to do this? And what good is it?

Ok, if you are not aware, the GPS system operates like this. A constellation of 24 satellites in geosyncronous orbit are constantly sending signals to the earth. Those signals are picked up by GPS devices and with a bit of mathematical wizardry the position of the GPS device is calculated by, more or less, triangulation.

GPS devices operate by gathering the signals from as many sattelites as possible. The more satellites you receive, the better your position can be plotted.

Then there's the Wide Area Augmentation System, or WAAS. WAAS stations are ground based stations that also transmit information in order to get an even more exact reading. Ok so that's a kindergarten explanation of GPS, but hopefully you get the idea.

So how do you shut down GPS access to, say, New York? Obviously you could simply shut enough of the GPS system down so no one in New York could get any readings. But look at it this way, it takes a minimum of two or three to satellites to get a decent reading of your position. My GPS unit receives about 7 or 8 satellite and WAAS stations on any given day, so to take down one city you'd probably have to take down 5 or more satellites and/or WAAS stations. You could probably plot the coverage areas of the satellites to know precisely which ones to shut down, but you'd still have to shut down a bunch of them. The problem with this is that it would probably knock out GPS service on a good fraction of the eastern seaboard, and GPS is fundamental in many facets of modern life, from air and rail transportation to telecommunications systems to the rescue and military operations that will be mobilizing during any terrorist attack.

So how else could you knock out GPS servce in a localized area? The only alternative I can think of is by using GPS jammers, which are widely considered to be ineffective. But that gives us another problem. You either have to know where a terrorist attack is going to happen and get a jammer there before it takes place or you have to have jammers in every city in the country.

But there's an even larger fundamental problem with this whole idea. How do they expect it be effective? What is the threat model in which they think this will come in handy?

Most terrorist acts involve blowing something up with a car bomb, doing something with airplanes, or just shooting some people. None of these require GPS. What's more, even if they did, you'd have to know the attack was being carried out beforehand in order to flip on the jammers. You'd also have to know that the attack relied on the GPS system in some way. You wouldn't hafta know for sure, you could just disable GPS anyway, but in the history of mankind there's never once been a terrorist attack that the loss of GPS would have stopped, so why screw everyone else up based on the remote possibility? This is still assuming, of course, that they knew about the plot beforehand any damn way.

If any GPS disabling system were invented before 9-11, it would have had zero effect. Presumably, aircraft without GPS would have a harder time navigating, but the terrorist pilots on 9-11 flew visually, and maps work almost as well as GPS in a lot of circumstances.

In short, I can think of no good way and no good reason to implement a system to disable GPS in case of an terrorist attack.

"What are they thinking?"



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