I can never quite wrap my head around it or figure out if they are all the same idea, or what, and what exactly the idea is.
In particular, the article soften describe something that “could replace GPS.” But then they start taking about compasses, and things that sound a lot like IMUs. Integrating accelerations is well known as a bad way of keeping track of position over longer timescales due to catastrophic cancellation. A more accurate IMU might let you do it for a little longer, but eventually you need an absolute reference point to correct your drift.
But then, sometimes there are references to making very careful measurements of the change in the gravitational field. So maybe those could act as landmarks or something?
I wish there was an article for people who, like, had a control theory or signal processing class, but it was too early in the morning and not very interesting.
This used to be mostly a military problem. No longer.
GPS is no longer reliable enough for civilian aerial navigation in much of eastern Europe and the Middle East.[1] "Most recently, for the one-month period from July 15 - August 15, 2024, a total of
41,000 flights experienced spoofing.
Because modern aircraft have incorporated GPS into a large number of aircraft
systems, the impact of a spoofed GPS signal has had severe and cascading
effects. These include the FMS, Hybrid IRS, the aircraft clock, GPWS, Weather
Radar, CPDLC, ADS-B and ADS-C, as well as numerous other systems."
GPS is so low power that spoofing signals now take out a large area of service.
> Because modern aircraft have incorporated GPS into a large number of aircraft systems
Aviation is slow. It wasn’t until recently that GPS-based landing approach became common, and even then you’re double checking with ground radar. No commercial airliner would use IMU—if ground-based radar is not operating or coöperating, you get out of that airspace.
There are many frequent flyers travelling on routes going through those regions, dozens of times each in the last year.
And they haven’t reported any noticeable issues caused by GPS spoofing, at least not that I’ve heard of.
So I’d be surprised if modern planes are designed such that the loss of GPS for an hour or two would cause issues severe enough to be noticed by even seasoned travellers.
Not to be a jerk, but you would be wrong. GPS spoofing is a growing problem in commercial aviation. So far it has not led to any fatalities, but it has led to a significant number of system malfunctions which degrade the safety features available to pilots.
One example that made the rounds on social media a few months back was a crew flying above 30,000 ft receiving "Terrain - Pull Up!" advisories. They ignored them, because there is no terrain on earth at 30k ft. If that had happened at a lower altitude, they would have likely had to do a terrain escape maneuver, which would definitely be felt by passengers, though it would likely not introduce a lot of additional safety risk.
The real risk comes when pilots begin to doubt that their safety systems are working correctly and thus ignore true warnings. Or when a bungled GPS leads pilots to fly into military airspace and get shot down.
Pilots can be instructed to ignore GPS related warnings and not trust GPS based systems for the one or two hour duration while they are transiting the jammed airspace.
Better yet they can be disabled temporarily since presumably the same proof can be shown to the relevant regulators, airline HQ, etc…
They aren’t automatons that must obey every single system installed in the plane regardless of how absurd the outputs are.
Yeah, I would guess that a spoofed signal wouldn't be that hard to detect - though you'd presumably need the GPS receiver to be capable of this. A spoofed signal would have to be stronger than the real thing in order to drown it out, no? So as a first guess - if a signal is unreasonably strong, the signal is probably spoofed, so warn the operator.
My understanding is that by using "the magic of quantum", accelerations can be measured with 0 error (for practical purposes), so it's an incredibly accurate dead reckoning positioning system. In that way, it's "GPS, but better" because you can't be jammed or lose signal. It would also work under water or under ground.
That's the gist of it, yes. The big advantage atom interferometers have over classical IMUs is that they do not need to be recalibrated every so often. They are thus often called "drift free". That still means that you need to compare your position with a reference after a certain time, but the position uncertainty is much lower and only determined by the error accumulating from integration, not due to the instrument itself degrading over time and introducing systematic errors. The reason here is not really "quantum magic" but rather the fact that the reference for the measurement is a laser beam which can be controlled with remarkable precision and accuracy.
Inertial navigation can be paired with GPS (and friends), terrain recognition, etc. to keep it accurate, and it can be used to detect jamming attacks on GPS. You can even use fairly low accuracy IMUs to detect jamming attacks on GPS, so it's certainly worth using.
With enough accuracy the frequency at which an IMU needs to be recalibrated with GPS or other systems can be low enough that a ship need only do it when at port, or a plane need only do it when parked or at an airport gate. I.e., at places where differential GPS can be available and/or where location can be known statically since the location only changes due to continental drift (i.e., very slowly).
Only when you're on the ground in the first place. Otherwise, you have a circular problem: past a certain point your IMU needs a gravity map to remain accurate, else the drift from variations in gravity is larger than the drift in your sensor. And you need to know where you are and how you're moving to measure gravity.
They also vary over time or something, right? So even a more precise measurement device, to get better gravity maps, doesn’t solve the problem… maybe? This is all based on half-remembered other comments.
So I would like to learn more about gravity map matching. I've seen offhand references to it in context of placing an ICBM on target (can't find ref now) but that's it. I imagine it is, (or was for long enough to make info sparse) a classified piece of know-how.
For sufficiently accurate IMUs, like the ones found in ICBMs, you need a gravity map because otherwise the variations in gravity cause your position estimate to drift
There's also the tides, and variations in the tides with 2nd and 3rd order effects on gravity. Absolute references based on variable references is ugly!
> Motion sensors in wearable devices are usually sensitive to accelerations in the range of [milli-gs]. Bigger, more expensive accelerometers ... on the order of [0.1 mill-gs]
> More accurate than either of these mobile accelerometers are cold-atom interferometers. These currently have sensitivities of [nano-gs], with future potential for [femto-gs], Kodigala says.
If Sandia is revealing this, they probably have a secret version that is already being loaded into cruise missiles and ICBMs. Seeing what’s happening over in Ukraine, it has to be clear to every military in the world that GPS is no longer of much practical use on its own.
US military systems have always been based primarily on inertial guidance as a matter of policy. They may take optional GPS corrections for small improvements in precision but they don't rely on them. GPS was never really designed to be a navigation system, even though you can use it for that; the military designed it to be a measurement system. The Soviets could have destroyed it the day it was built, it was strictly a peacetime tool.
Also, what gets exported to Ukraine is intentionally downgraded in many cases, at least from the US side. Much of what they receive was state-of-the-art circa 1990s or earlier.
So, remembering the exact location once, and then tracking all movement with almost absolute precision, thus calculating all future locations? Did I get it right?
Basically yes. If you want to get technical about it, it's not tracking movement it's tracking acceleration, which you can then integrate twice to update position.
Technically, acceleration is movement in an inertial system... Anyway, I was wondering for a long time, why phones/watched don't attempt to do it (at least, I never saw useful results of it). Surely it would be more useful to me than nothing, when lost in a labyrinth underground. I always assumed, that results are so horrible (close to random) that nobody even bothers. But then it doesn't tell me much if there is an accelerometer 1000 or 1M times more accurate, in a shoe-box or otherwise. Like, how often does it have to re-calibrate after all?
Are there any records of how currently available consumer devices measure up in this regard?
I read a paper some time ago which suggested that mobile devices are still nowhere near good enough to use this e.g. for navigation around a shopping mall.
While ships are big, there is a lot they want in them so space tends to be limited if the ship wasn't designed to do that. Military places the big things and the rest in between
They've been in use for years now in that war. The Shahed drone, for example, was used by Russia. About two years ago Ukraine was using autonomous drones to down Shahed drones.
AI targeting came out in the Gulf war, friend. 35 years ago, Tomahawks could use rudimentary AI to match preprogrammed terrain profile and target imagery to get more precise targeting.
The Shahed drone can't use it's INS system to communicate with a ground operator or reprogram itself. As the other comment says, it's basically a glorified cruise missile that has the autonomy of a Roomba. Disabling a Shahed with another drone may have happened, but it's certainly not the primary threat to the Shahed when compared to CIWS or SAMs.
AI targeting was debuted in the Patriot missile system, which does technically field the required elements of a hands-off kill chain. But TERCOM is not AI nor was it debuted in the 90s with the TLAM. The original BLOCK-I variants of the Tomohawk (and many versions released afterwards) were no more autonomous than the Shahed-136.
Thankfully, the same measurement technique can be used to measure e.g. gravitational fields, and there are already devices available on the market which surpass classical gravimeters in accuracy and precision. There are also satellite missions in the planning to map Earth's gravitational field with atom interferometry.
More specifically, nuclear arms, where the budget is "there is no budget." Just the inertial guidance system of a 90's-era ICBM cost over six figures per missile. The ability to precisely place a missile without any external navigation (except for stars.)
Once it gets cheap enough, it'll probably go into cruise missiles; it could eliminate or reduce the need for terrain contour matching, which requires radar transmission.
I'm not 100% certain but I believe when MEMS accelerometers first came out, the better ones were subject to arms controls because of fears they could be used in missiles.
In Russia's case, there does appear to be "no budget". The weapons were intended as a last resort, and so they are a great target for diverting maintenance funds.
It's not quite so bad as "we are certain that they will not successfully launch any nukes" and so they're still being treated with caution. But the US keeps upping what it allows Ukraine to do as it loses its fear of World War III.
As it applies to the US... yeah, the sky is the limit for military spending.
There is no fear of WWIII, that's part media invention, part political excuse, part useful idiots. A "World War" requires an opponent worthy of a world-wide conflict, and Russia is anything but, being stuck in Ukraine for three years and losing most of its army in the process. Conventionally, Russia is no match for NATO, with enough political will it'd be a Desert Storm-like curb stomp. The only way it's not is the US abandoning NATO, then it can be quite painful, but even then Russian economy is no match for the EU.
As for nuclear weapons, they are practically useless. Anything but strategic use would have little impact on the battlefield, but will immediately alienate China and India. They have their own border conflicts and do NOT want the nuclear taboo to be broken, and they are holding the leash, being the only economic and technological lifeline Russia has. A strike against the US would be suicidal for obvious reasons.
Also, notice how Putin and his officials talk about nuclear use a lot, but there is still zero evidence of any action (such as dispersal of road-based ICBMs or 12th GUMO taking warheads out of storage). Rhetoric is cheap and not credible.
The only real fear of escalation here is "horizontal" escalation: Russia stirring shit elsewhere. Advanced anti-ship missiles to Houthis, handing nuclear technology to North Koreans or submarine technology to China, that kind of thing. But that's already seem to be happening, and there isn't much more that Russia can do.
To drive this home, India and China have a moderately high probability of engaging in armed conflict with a nuclear power in the next decades. (India with Pakistan and China, China with America.)
They do not want tactical nukes to be normalised in prelude to those conflicts.
There is no fear of WWIII, that's part media invention, part political excuse, part useful idiots.
Not true at all. The risk may be overstated by some, but it's a perfectly possible outcome that must be considered.[0]
A "World War" requires an opponent worthy of a world-wide conflict, and Russia is anything but
Also simply not true. It just requires one side to start using nukes, which can also happen entirely by accident (and has come close to happening multiple times, even without a multi-year and incredibly nasty hot proxy conflict on the ground between two of the planet's largest mutual adversaries).
As for nuclear weapons, they are practically useless.
True of course, but it doesn't matter. What matters is that certain people might start to think that they're useful and/or their only choice. Which gets into the fact that we can't assume these people are acting rationally.
Also, notice how Putin and his officials talk about nuclear use a lot, but there is still zero evidence of any action
Right, but that can change at any time. It doesn't even have to be a tactical battlefield strike (which of course would be useless, and their people know it). For example, once their backs are pushed against the wall with sufficient firmness, Putin or his successors might start to think that a demonstrative high-altitude detonation over an ocean somewhere might be a pretty neat idea. Especially if they've reached a point where they have nothing more to lose, and have a reasonable fear of being outright killed sooner or later if the current situation on the ground starts to move strongly and rapidly against them.
I don't think there is any conceivable scenario in which Russia using nuclear weapons would lead to anything resembling "World War", except Russia launching a counter-value strike against continental US, which is just not happening. A high-altitude detonation is not a "World War".
Russia is a China's client state at this point, and China is very interested in keeping nukes taboo. They are so worried their own army is only allowed melee weapons in border skirmishes with India. There is no way a demonstrative breaking of the taboo would not get Putin's leash yanked, so even that remote possibility (that has nothing to do with WW3) is extremely improbable and would only hasten Russia's defeat. Unless, of course, our politicians use it as an excuse to abandon Ukraine.
Also, no one is "pushing Russia's back against the wall" in Ukraine, there are no M1A2s speeding to Moscow. Russia understands it perfectly well, too, denuding their borders with NATO to throw more soldiers into the meat grinder.
> the fact that we can't assume these people are acting rationally
I think this meme is largely a cop-out. A person just doesn't get to be a leader of a country by acting irrationally. They might interpret things differently or have different priorities, they might even put on an act of irrational buffoonery, but it's different from being "irrational". However, to see the rationality of their actions requires putting yourself in theirs shoes, which is uncomfortable and/or requires a deeper understanding, so it's easier to just write their behaviour as "irrational".
Putin is perfectly rational. The empty threats are working (as evidenced by this thread), there is no risk of a strategic exchange (because the actual signalling on the ground is one of business as usual), and Western politicians are successfully convincing their voters that they drag their feet because WW3, not because actually stopping the war (eg deploying a NATO peace keeping force) would incur a substantially higher domestic cost.
We don't really talk about potential North Korean aggression in WW3 terms, do we? We shouldn't do that in Russian case either.
Obviously (as in very obviously) this wouldn't be the big one in itself, but an entirely possible provocation that could shove things in that direction.
China is a significant inhibiting factor, but one factor among many. "Client state" is a caricature, the relationship is more complex than that.
Also, no one is "pushing Russia's back against the wall" in Ukraine, there are no M1A2s speeding to Moscow
It doesn't need to be tanks speeding to Moscow. A major shift in the ground situation Ukraine's favor (effectively signaling an eventual Russian defeat) could do the trick.
Also no one said this was presently happening, so your use of the present tense is puzzling here.
Putin is perfectly rational.
He isn't simply "irrational", but he definitely isn't "perfectly rational" either. Otherwise, he wouldn't have bullied his own advisors to a point where they were afraid to express their own opinions (or even provide rational assessments) in regard the neat little plan he decided to roll into action in the Fall of '21. And what he apparently does in all seriousness believe about his own manifest destiny (as the restorer of the Motherland's natural position of greatness) definitely isn't rational.
There's also the matter of his successors, who won't be nearly as smart, and will likely be far less rational.
The empty threats are working (as evidenced by this thread),
I guess everyone who doesn't agree with your assessments is either paralyzed by irrational fears, and/or a useful idiot, or just looking for a cop-out.
> an entirely possible provocation that could shove things in that direction
How? What plausible pathway do you see between Russia exploding a nuke over Novaya Zemlya and their suicide by American nuclear response?
> A major shift in the ground situation Ukraine's favor (effectively signaling an eventual Russian defeat) could do the trick.
I don't understand what trick. Russia directly attacking NATO? They'd get pulverised, and they have no forces left. Russia committing a suicide by launching a strategic attack on the US over Donbas? That's implausible. They just lost a chunk of Russia proper and took it on the chin.
> I guess everyone who doesn't agree with your assessments is either paralyzed by irrational fears, and/or a useful idiot, or just looking for a cop-out.
I see how it's easy to interpret the earlier reply personally, my bad, sorry. I was referring to the people establishing the narrative (media, politicians, and people with large platforms). It's self evidently working! A direct confrontation with Russia (a country with an economy smaller than Italy's, glaring manpower problems, and largely depleted army) evokes the idea of WW3, but I see very few people talking about the very likely war over Taiwan (with a much, much, much more powerful country) in "WW3" terms. This narrative doesn't make any logical sense, we just got used to it, even though it's not grounded in reality.
Nuclear arms doesn't need as much accuracy as other weapons though: when using a cruise missile or a glide bomb with a few hundreds of kilograms of explosives, you need metric precision to get the military effect, when the payload is a 100kt bomb, then 100m is accurate enough.
Unlike other bombs it must absolutely be 100% resilient to any kind of spoofing though, for obvious reasons, hence GNSS is a nonstarter for those when they are the default guidance system for other weapons (with backups, for cruise missile).
It makes a difference for hard targets, see the new nuclear "super-fuzes."
It can take several warheads to destroy a missile silo with high probability, because even landing a little off-target can spare the silo. Greater precision means it takes substantially fewer.
My point was that nuclear missile development gets a blank check and I cited the over-six-figure intertial guidance units in 80's and 90's era missiles as an example of this.
I'm not sure what point you're trying to make here?
Accuracy is incredibly important because you don't put a nuke somewhere to kill people; you put it there to destroy infrastructure. More specifically nuclear missile silos, and bomb shelters (well, the people inside them.)
Reducing the CEP means you can use a smaller nuclear yield to get the job done, which is preferable for a number of reasons, including politics, but also allowing for more targets in a strike.
The very latest US ICBMs are suspected of having sub-100m CEP. CEP for ICBMs is "bad" enough that it is typical for planners to figure three warheads per target, but accuracy is rumored to be getting good enough where that is no longer necessary.
> you don't put a nuke somewhere to kill people; you put it there to destroy infrastructure. More specifically nuclear missile silos, and bomb shelters (well, the people inside them.)
It depends.
"Counter-force" strikes aim to destroy the ability to respond or attack with nuclear weapons, not infrastructure per se. So that's just silos, warhead storage sites, submarines in port, airfields, etc. The US is doctrinally counter-force for about half a century. This doctrine is also reflected in technological choices: lower yields and higher precision mean lower fallout, collateral damage, and fratricide when hunting for silos, but aren't that useful for city busting.
"Counter-value" strikes are pure destruction of cities and killing of people. Russia seems to have this doctrine [1]. This is a very inflexible doctrine, because you can't credibly threaten to execute a counter-value attack on the US over things that don't seem to be worth a response in kind (like a defeat in Ukraine). It's much cheaper though.
> The very latest US ICBMs are suspected of having sub-100m CEP
[1]: At least strategically. There is a hybrid strategy of targeting military-related infrastructure, which Russia seems to have adopted for less-than-strategic forces according to recent leaks https://www.ft.com/content/237e1e55-401d-4eeb-875b-03fe68f81... .
That could be the point of sentiment around this tech. Most funded development is done out of military R&D instead of science/consumer/art purposes. Everything else ends up benefiting eventually but it would be nice if we didn’t only create things for war and then later repurpose them for everything else.
The main application would obviously be missiles and autonomous military drones. If you can use GPS - you should. It's crazy cheap and it doesn't accumulate errors over time. But in a war GPS can be jammed. This can't.
INS incl. LRG has been a thing for decades. The modern problem is over-reliance on GPS (military coded and commercial). QINS would solve many issues but GNSS is also still needed to calibrate the system at least initially (at launch) and opportunistically mid-course. The other thing that is being fielded, despite its downsides and vulnerabilities, is wire guidance a-la TOW.
There was a big cheapening when the military miniaturised fast gps so small and cheap it could be put into artillery shells. This was very effective when Excalibur and himars first arrived in Ukraine.
By the time the small diameter bombs had been married to a rocket the Russians had effective and pervasive gps jamming and accuracy plummeted.
The older more expensive systems with ins like atacms maintained accuracy.
There's a Polish guy that volunteered in Ukraine building drones, he talked about this.
There are tricks to avoid most of the GPS jamming, long-distance drones use them (he said the evolution is crazy fast, every 3 months there's new techniques deployed) the traditional military systems can't be modified in 3 months so they are more vulnurable.
They are constantly changing the video and controlling frequencies, there is some AI appearing, a big change was flying signal repeaters, there are tethered flying drones with rolls of fibre for steering/video that are completely invulnurable to jamming. Often they also have cables for power, so they can stay in air forever.
But even in the cheapest drones there are ways to deal with it. For starters you shield the GPS from the bottom half-sphere, and you put 2 GPS receivers at opposite ends of the drone and compare the signals. Jammers are closer than sattelites, so the difference between the signals sampled 2 meters apart will be mostly the jamming, and then you can remove it.
It's not perfect, but it's good enough for the drones to hit the targets most of the time. And they obviously have cheap accelerometers, compass etc - which is basically INS, just less accurate. So it's sufficient to get by through the region with jamming, and to recognize when GPS is spoofed.
Yes, existing gyroscopes are sensitive enough for that. In 1966, one of the first Soviet attempts to launch the Soyuz failed on the pad because the guidance system remained active after a scrubbed launch attempt. After a couple of hours, the Earth had rotated enough such that the guidance system thought it was off-course, triggering the still-armed launch escape system.
> The motion of the solar system?
This system, probably not. This class of system at lab scale, maybe eventually. It seems that the galaxy's gravitational acceleration on the solar system is on the order of 10^-10 m/s (https://www.sciencedaily.com/releases/2020/12/201203133906.h...), so about 10 pico-g. The article says that cold atom interferometers have current sensitivities in the nano-g range but could still potentially improve.
> By watching vibrations could it be a microphone?
With that kind of sensitivity, making it not be a microphone is probably the harder task. However, the sensitivity doesn't necessarily make it a good microphone, since detecting a small signal is useless if the signal-to-noise ratio is too low.
> that the galaxy's gravitational acceleration on the solar system is on the order of 10^-10 m/s
A free falling accelerometer (that is an accelerometer that moves along a spacetime geodesic) will detect no acceleration. And the solar system "free-falls". I don't see how we can detect that.
Points on the Earth's surface are experiencing an acceleration- after all, after 12 hours their velocity has changed direction by ~180 degrees.
You can detect Earth's rotation with a sufficiently large pendulum[0] or a good gyroscope. Something with enough inertia will tend to refuse to rotate with the planet, which lets you compare the two and infer the absolute rotational speed of the planet.
For the first two questions I wouldn't think so because it detects acceleration. But I also only have a high school level of physics knowledge so maybe I'm wrong.
Anything rotating is experiencing acceleration, you can tell whether your merry-go-round is spinning or not with your eyes closed: that's the acceleration.
> Could one derive the Earth's rotation? The motion of the solar system?
It's not a motion sensor; it's an acceleration sensor. That's an important distinction because the primary problem with IMUs is that they work of changes in velocity, and error in those measurements slowly accumulate - so they almost always need external references to correct for accumulated drift.
https://news.ycombinator.com/item?id=40692333
for example.
I can never quite wrap my head around it or figure out if they are all the same idea, or what, and what exactly the idea is.
In particular, the article soften describe something that “could replace GPS.” But then they start taking about compasses, and things that sound a lot like IMUs. Integrating accelerations is well known as a bad way of keeping track of position over longer timescales due to catastrophic cancellation. A more accurate IMU might let you do it for a little longer, but eventually you need an absolute reference point to correct your drift.
But then, sometimes there are references to making very careful measurements of the change in the gravitational field. So maybe those could act as landmarks or something?
I wish there was an article for people who, like, had a control theory or signal processing class, but it was too early in the morning and not very interesting.
reply