New laser could cram GPS alternative into a shoebox
spectrum.ieee.org
spectrum.ieee.org
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.
A part of me was subconsciously entertaining that a subsystem of the IMU / INS was actually being used to provide gravimetric navigation (producing a coarse global position update de novo rather than correct for an error-prone open-loop one from an a priori generated gravity map). a la
https://ieeexplore.ieee.org/document/9059124
or
https://www.researchgate.net/publication/343278497_Analysis_...
> 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.
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.
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.
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.
(Ops Group is a professional group for international pilots, flight planners, or, as they say, people who have a callsign or answer the phone "Ops".)
Besides, it is hard to determine when and where jamming will happen, and it can start and stop at any time. Imagine a truck driver trying to bypass their company tracking using a small jammer, and driving down the coastal highway near SFO. Any planes coming in for landing might lose GPS or even worse, get inaccurate results, but only for a moment or two. Is that a problem? It depends on exactly what the plane is doing in that moment and whether everything else is going right.
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.
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).
Document enough millisecond pulsars and find your position anywhere in the galaxy.
When signal reception and computing power get powerful enough, put it on your wrist.
I still haven't heard of any major breakthrough in the size of our batteries but when that comes we'll be miniaturizing literally anything.
Maybe they will even use some kind of super capacitors instead of batteries.
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.
Are there any records of how currently available consumer devices measure up in this regard?
https://github.com/nisargnp/DeadReckoning
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.
https://en.wikipedia.org/wiki/AGM-158_JASSM
> Guidance system: GPS, INS, IIR
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 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.
ICBM warheads are small. Space in drones and fighter jets is at a premium.
This is military.
Could one derive the Earth's rotation? The motion of the solar system?
By watching vibrations could it be a microphone?
And this vector right here.... that's the milky way's orbit about the greater magellanic cloud...
This device will track acceleration rather than velocity
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.
Is that... assful?
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.
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.
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.
GPS signals can't be signed because the signal bandwidth is limited, a digital signature is going to take hours to get transmitted.
But by using something like a Starlink satellite, it's possible to transmit digitally signed timing packets that can't be spoofed.
So yeah, this should solve the spoofing issues for most cases. Low-orbit sats would be able to transmit a signature every millisecond or so, but that's not really necessary.
It'll be nice if they can get it small enough for a phone, though.
Depending on when the tech is available, preventing GPS jamming of drones is probably much more urgent in Ukraine.
HIMARS, on the other hand, will enjoy the improvements.
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 Shaeed is really just a rather shitty cruise missile.
https://en.wikipedia.org/wiki/HESA_Shahed_136 "No cameras or short-range sensors were noted in 2022."
> Tomahawks could use rudimentary AI to match preprogrammed terrain profile and target imagery to get more precise targeting.
Key word: preprogrammed, and similarly a cruise missile.
It's the FPV drones chasing down people in trenches that require real-time video transmission to control.
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.
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.
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).
Not accurate enough for counterforce. When a missile silo lid can withstand 600 atmospheres of overpressure, "close enough" isn't good enough.
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.
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
Apparently the precision is good enough for photos like the one on page 23 here https://www.osti.gov/servlets/purl/1557069
[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... .
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.
https://thebulletin.org/2017/03/how-us-nuclear-force-moderni...
Nuclear bombs are useful because you don't need precision to get the effectiveness, but if you have the precision then why would you bother with the consequences of using nukes…
If a superfuze or a super-IMU means that you can kill one silo with one nuke, that is a huge improvement over the old status quo, where it was assumed to take several, simply because the CEP was larger than the radius at which they can destroy a silo.
If someone does have an conventional ICBM that can reliably take out nuclear silos that would be an even bigger deal.
Of course the US military has been working on conventionally-armed ICBMs: https://en.m.wikipedia.org/wiki/Conventional_Prompt_Strike
But this kind of silos simply doesn't exist.
Yes you could theoretically imagine such a silo, but because the threat of a conventional bunker buster payload hasn't been very realistic when it comes to nuclear silos, they aren't designed to deal with such a thread and instead focus on protection against the kind of overpressure that is caused by an nuclear explosion occurring around.
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.
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.
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.
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.
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.
The "pathway" is that any deployment of a device will at the very least trigger a suite of necessary countermeasures on both sides (moving assets around and so forth), greatly increasing the risk of misperceptions and panic reactions.
I don't understand what trick. Russia directly attacking NATO?
The "trick", by which I mean outcome simply, of pushing the regime into an (acutely) fatalistic mindset. The reaction doesn't have to be a direct attack on NATO. It could be some other form of escalation (of the sort they might have ruled out otherwise). It doesn't even have to be an action taken by Russia. It could a matter of China looking at the situation and thinking, in terms of the move they've always been threatening to make, "now or never".
I'd rather not delve into scenarios; I'm just advocating that we observe the cautionary principle here. We agree that the risk is overstated, and that the aggressor's threats are mostly bluster. But it's definitely not negligible risk, in my view; probably on the order of 3-5 percent per year. As high as at any time since the Cuban missile crisis, in any case.
How is it different? What "panic reactions"? What "panic reaction" can connect a low-yield explosion over Black Sea and a suicidal strategic strike on the continental US?
> I'm just advocating that we observe the cautionary principle here
"The cautionary principle" is only applicable if you disregard hundreds of thousands of killed and maimed Ukrainians, millions of refugees, unknown number of abducted children, and entire cities raised to the ground. Letting a genocide continue for years is not a default safe option.
Again, I invite you to reflect on this exchange: you'd "rather not delve into scenarios", but when weighing what's basically just vibes against very material, prolonged, ongoing suffering of the second largest country in Europe you decide to advocate for vibes. Putin's bullshit has already won and his deterrence succeeded, because you give it enough credibility (whilst refusing to outline a credible scenario) to talk about "WW3" as a real risk worth more than dead and maimed Ukrainians.
How is it different?
From a detonation deep inside their own territory? You tell me.
a suicidal strategic strike on the continental US?
I never suggested that would be the next step. In fact my words said something entirely different.
For some time now I've been noticing a consistent tendency in your posts to employ straw man techniques. Then we have this:
Letting a genocide continue for years is not a default safe option.
you decide to advocate for vibes
you give it enough credibility (whilst refusing to outline a credible scenario) to talk about "WW3" as a real risk worth more than dead and maimed Ukrainians.
I'm doing absolutely none of those things. Unfortunately the conversation has definitely into unproductive territory, and you seem to be confusing me with other people you're unhappy with. I'm not those people and my energy resources are quite limited. Let's wrap up here and give the topic a rest, please.
If quantum INS can soon take out more Russian ammo dumps in spectacular fashion, then bring on improvements to lasers.