What country has ASATs? They'd need to be able to take out several satellites (I confess I don't know how many) to degrade the GPS constallation significantly. I think we'd see them making that level of preparation before it happened. Perhaps a message to whatever country this is, telling them that attacking our satellites would be an act of war, and we'll be gunning for them if they continue preparing, would suffice. Displacedjim

quote: [They'd need to be able to take out several satellites (I confess I don't know how many) to degrade the GPS constallation significantly] Theyb would also need to disable a high number of them concurrently as depending on location, there are satellites that overlap their paths for redundancy issues. Losing one won't kill off the capability to "see". 30 minutes later a remap will have happened if its a vital area.

Jim is right. We can not 'stop' them. But a realization of the consequences can deter them. Actually there are few countries technologically capable.

A backup system, based on orbiting sattelites with known orbits, could be developed. It's mathematically more complex and the receivers would need to be made for it, with a highly precise clock tied to it and the ability to know that at this instant, the sattelites should be here, here and here. But it seems very doable, though possibly somewhat less precise.

I don´t think you really need a especial ASAT system to destroy GPS sattellites(they are not so many). As you know most sattellites travel at a predeterminated orbit, and it won´t be so dificult to build something to colide with then or just fragment in their path(even if it is ground controled). A country that can put men in space could simply go there an kick your GPS sats away. Sure, it will be a very expensive hard work , but everything would be better than having thousands of JDAMs or JASSMs falling on your head. I think China and russia already have somethings secret that we do not imagine. They are not so stupids!

Well, you'd need to knock out the US GPS sat's but also (soon) the EU sat's. So you'd need to knock down a lot of them. And even than, they'd be quickly repositioned. Somebody said that you could put something in orbit and let the sats crash into them. well good luck. The sats are not all exactly on the same height. they differ a few km. Anybody want to put an object a few km wide into space?

Rendezvousing in space was first accomplished in the early '60s with computers made out of vacuum tubes and magnetic core memories. An orbital rendezvous is easier than a direct intercept because the interceptor approaches much, much slower providing lots of time to adjust trajectory. The direct intercept is like hitting a speeding bullet with another speeding bullet. It's been done, but it's hard. Problem for bad guys with orbital intercept is that the space tracking folks in Hawaii and other places will have a chance to detect the ruse and sound the alarm. There are a number of spare GPS satellites in orbit, so a minimum number have to be taken out before service starts to degrade. As more satellites go down, there will be larger and larger windows of no service. The near simultaneous intercept of a dozen or more satellites may not be technically feasable for some time. The fact that attacking the GPS constellation would be perceived by the US as an act of war would not be a deterent. If a country has decided to attach the GPS system, they have already declared war on the US. Attacking the satellites is just the opening round.

Who would be foolish enough to try and destroy US GPS sattelites???? I mean: The US forces would drop into backup mode with oldfashioned methods (mapreaing perhaps) other PGM from the toolbox. GPS is used because it is convinient. AND UPSETTING THE CONVIENIENCE OF US FORCES IS UNWISE. You might be forgiven for shooting at them (if you live that long), but upsetting their beer is tantamount to asking for severe trouble.

Yes, it will be an act of war. The Folks in Hawaii and other places could easly see what is happening but, there will be nothing they could do about it. There are a half dozen GPS spare sattelites in space and using then will let you without reserves and vulnerable to technical failures. The americans still can win most wars without their GPSs, but it would be much harder and slower than previous tought, and they will have many more losses and casualities.

"Somebody said that you could put something in orbit and let the sats crash into them. well good luck. The sats are not all exactly on the same height. they differ a few km. Anybody want to put an object a few km wide into space " Uhm, it would not need to be one solid block - it would be sufficient to fragment something comparatively large in space and the fragments would take care of all the satellites including any spares.