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asynchronous13 656 days ago | link | parent

Egads, the news coverage of this is horrible fear mongering.

The researchers from UT built a system to protect against GPS spoofing. In order to prove that their protection system works, they had to demonstrate that GPS spoofing is feasible. Without exception, every news item on this only mentions the spoofing part, and not the protection part.

Military unmanned systems use encrypted GPS that is not vulnerable to the attack demonstrated.

Its possible to make a vehicle fly erratically, or even cause it to crash by spoofing GPS. But to take control requires a lot more than what was demonstrated. An error of 1us in the spoofed signal corresponds to 1000ft -- that's why the actual descriptions of the vehicle say 'banked hard' or 'veered' off course.

GPS jamming is so much easier than spoofing and results in the same thing.



rabidsnail 656 days ago | link

> GPS jamming is so much easier than spoofing and results in the same thing.

Does it? Can't the drone tell that the GPS input that it's getting is inconsistent and fall back to flying home using dead reckoning?

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asynchronous13 656 days ago | link

Technically, yes it is possible for an autopilot to use dead reckoning for navigation without GPS at all. (we didn't use GPS to navigate to the moon, right?) However, all commercial autopilots that I know of rely on GPS to some degree. The difference is the use of low-cost gyros and accelerometers. They are good enough when augmented with GPS, but not good enough all alone.

Edit: the low-cost sensors can be augmented with sensors other than GPS too, like vision processing. This has been demonstrated but is not yet in widespread usage. I expect to see this become more common due to demonstrated vulnerabilities in GPS.

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jandrewrogers 656 days ago | link

State-of-the-art inertial navigation technology has approximately the same precision as state-of-the-art GPS. Even modern run-of-the-mill interferometer-based inertial systems are precise enough for most purposes.

The unique value of inertial navigation is that it requires neither receiving nor sending a signal that can be jammed or spoofed, hence why the military uses it for everything.

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asynchronous13 656 days ago | link

1960's inertial navigation systems have better resolution than today's consumer GPS. The issue is not the technology, it's the cost, size, and weight. The small, light, and low-cost sensors fueling the current wave of UAVs are not the most accurate technology available, but that doesn't mean they aren't useful.

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einhverfr 656 days ago | link

The concern I would have with inertial navigation over long distances is the possibility of drift. You might have good resolution over short distances, but what about hours and hours? What if your vectors are not quite right, or you get drift in your gyros (and LR gyros are prone to drift in certain circumstances)?

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runjake 656 days ago | link

Which is why aircraft normally have multiple INS units. INS has been used as primary nav for endurance missions (>24hrs) in the US military for decades.

Citation: Myself, I worked on a variety of systems including INS and GPS in the military.

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einhverfr 656 days ago | link

But redundant INS units protect against failure of LR gyros. They don't protect against the case where an extremely slow turn by the plan can induce drift in an LR gyro. In that case all your redundant systems will all drift together.

LR gyros are also limited by physics to a certain limit of precision, and this is the specific mechanism by which they can drift (from what I understand though building larger gyros might help). So flying for a long time.... I don't know to what extent we know how much drift might occur. It would certainly be possible to build in some checks here though since landing in Iran instead of Afghanistan would seem to show some discrepancy between the two systems.

I am just not sure you can be sure that relative position will be as accurate as absolute position over an extended period of airtime.

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jessriedel 655 days ago | link

> But redundant INS units protect against failure of LR gyros. They don't protect against the case where an extremely slow turn by the plan can induce drift in an LR gyro. In that case all your redundant systems will all drift together.

I'm am pretty sure this is very wrong, although I'm not an expert enough to downvote you. Having multiple systems allows one to average out (statistically independent) drifts; it's not just a protection from failure. I don't think there's anything special about a "slow turn" which will cause military-quality INSs to have correlated drifts.

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einhverfr 655 days ago | link

As I understand it with LR gyros, if you rotate them sufficiently slowly so that they move less than half a wavelength in the time the light transits, they re-lock on the new orientation without interference. This is a limit based on quantum physics and it's why I said that larger gyros might reduce the problem.

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jessriedel 654 days ago | link

Well, if so I think this is an issue that designers of military systems have been well aware of for years. Drones don't seem any more at risk than submarines, which have used INSs successfully for decades. Drones seems much less likely to go through large stretches of time without access to GPS than submarines, so I'd be surprised if it's an issue.

I think the real problem is that INSs are simply to bulky and heavy for drones, rather than anything to do with drift.

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runjake 654 days ago | link

This is incorrect. They aren't just there for redundancy, they are there to account for gyro 1 vs 2 anomalies (drift).

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anothermachine 655 days ago | link

Why is this HN thread the only Google result for "LR gyro" ?

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einhverfr 655 days ago | link

The full term is laser ring, or ring laser gyroscope.

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JabavuAdams 655 days ago | link

There was a fratricide in Desert Storm where a bunch of Apaches drifted behind friendly lines. INS is mentioned as a contributing factor. IIRC they were hovering, but a slight wind didn't register with the INS.

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rdtsc 656 days ago | link

Extra bonus points : if you get above the cloud cover, can also use constellations to correct accumulated errors.

I heard some Russian ICBMs had a special window so that cameras can see constellations for that purpose.

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wazoox 655 days ago | link

And the SR71 had it from the start, too.

http://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird#Astro-...

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sneak 655 days ago | link

Oh wow, this is why I keep coming back to HN again and again. Thank you for teaching me something amazing!

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Cushman 656 days ago | link

Out of curiosity, how precise are we talking? I assume the top-level military tech is classified, but if I buy off-the-shelf parts, how far can I fly and still land on the runway using pure dead reckoning?

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philip1209 656 days ago | link

I would expect a secondary form of navigation. Submarines and even Google Maps cars use an inertial guidance system - if GPS is lost or clearly spoofed, you can rely on the inertial guidance system long enough to set a trajectory for a safe zone.

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erikb 656 days ago | link

Do you have some reasonable sources about GPS jamming? From what I know, GPS should be protected against jamming through signal spreading, which means you should be only able to do it with investing unreasonable amounts of resources.

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asynchronous13 656 days ago | link

Is this good enough? http://www.jammerall.com/categories/GPS-Jammers/

Low-cost GPS jammers are $30-$50 dollars, though they are illegal to sell or to use. Jamming is a simple matter of sending out a signal more powerful than the signal received from the satellites. 100mW transmitter is more than adequate in close range.

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lallysingh 656 days ago | link

> GPS jamming is so much easier than spoofing and results in the same thing.

If that drone is in a homogenous-looking area, say a desert with litte habitation, it wouldn't be hard to slowly get the drone to a different target than desired, possibly having it think another car or house is its target.

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