Tom Clancy Drool-Fest
Cool little report from Jim Dunnigan:
A new method of defeating GPS jamming was used in Iraq. The method puts GPS signal boosters on UAVs or other aircraft that can stay in the air for a long time. These boosters take the GPS signals from satellites and amplify them, often enough to overcome GPS jamming. These “artificial satellites” are called “psuedolites” and will work as long as the using side has air supremacy.
An amazingly simple fix. Simple, that is, until you consider everything behind it. GPS requires launching an entire constellation of satellites in orbit, keeping them there, and launching improved replacements as needed. It requires receivers able to discern weak signals from multiple feeds over a hundred miles in the sky. The jamming fix requires an Air Force able to build, maintain, and fly remote-piloted drones. Those drones have to be small enough to be somewhat stealthy, but large enough to carry effective radio signal-amplification gear.
In short, you need a world-class space industry, advanced micro-electronics, and an imaginative, well-funded military.
Sorry, did I say something about a “simple fix?”
Actually, I’m going to have to think about it some but I don’t think Jim’s explanation makes sense given my understanding of how GPS works.
GPS Jamming? What are these people smoking? The only way to jam GPS in the context of guided weapons is to get between them and the satellites. That requires a fairly large plane; one which is putting out enough EM noise to light it up light a christmas tree for anyone who happens to be looking for such things.
Like, say, F15′s. Anything that was silly enough to try would be taking the express route to zero altitude really quick like.
Further, military GPS operates on an entirely different system than the civilian version. It’s virtually impossible to Jam to begin with, much less doing so with bombs that are looking UP for sat data.
Re: Mr. Lion
Actually, we learn ahead of schedule that the GPS jamming is not science fiction during the last round of Greek armament precurement process. Several countries were invited for weapons demostration. British and American official were puzzled on the sudden inaccuracy of their equipements. The German won that round of contracts. It was later disclosed that the French government, in an act of sabotage, uses GPS jamming to try to ‘even the playingfield’. Tood bad they didn’t win the contract either.
I believe it is from that experience that the current round of GPS signal boosting technology was developed.
Weapons that were made prior to the advent of antijam/antispoof are vulnerable; those made after much less so.
Airborne signal amplifiers won’t work. First, anything you do to the signal is going to change the timing. Second, no matter how hard you try, you’re going to change the timing because you’ve changed the path the signal travels through. Third, anything with CRPA antennas is going to attenuate anything that’s not on line of sight to the satellite.
That said, I’d have to crunch the numbers to see how bad things could get. Light travels 300 meters per microsecond, so you can assume that the propagation delay on these things has to be quite small. I’m thinking on the order of ten nanoseconds. The alteration in path itself is definitely a factor; the GPS satellite basically sends a signal that says “my current time is this”; when you get it you can figure out how far it is away using the speed of light. Any deflection of the path away from direct adds the perpendicular distance from the pseudolite to the path, to the distance that gets calculated. Even if this distance is only a mile, you get a mile of position error.
I’m not sure airborne conventional GPS can support a weapons mission. Even if you pretend you’re a satellite, the ephemeris data rate is extremely slow, and nothing airborne has slowly moving ephemeris parameters.
I’m not a GPS expert by any stretch, but I’d have to see a whole lot more about how this was mechanized to believe it.
BigFire: Sorry, I don’t buy it.
Even in the highly unlikely event of jamming the military GPS system locally, all of the GPS-guided weapons in the US arsenal have accomodations for a loss of direct GPS signal to the weapon. It is generally in the form of an internal navigation system that will develop a navigation formula based on an information handoff from the plane it is dropped from.
I suggest you read what Sparkey over on Sgt. Stryker’s site has to say on the matter. He’s actually worked with the weapons.
David was discussing what I was thinking about the way GPS works. You can’t just repeat the signal.
Yes, Robin.
One caveat: this is in fact the way GPS works. The thing I’m being very careful about is that there may be some new things in the aided navigation field that I’m not aware of. It may just be possible that what they’re doing is setting up differential GPS or some other alternative to GPS. What I don’t understand is how to make such a setup work with conventional weapon GPS receivers.
pl tell how gps can be jammed