Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

New laser could cram GPS alternative into a shoebox

spectrum.ieee.org

Post reply on HN
Print view View original

71–80 of 103 posts

Re: New laser could cram GPS alternative into a shoebox

#71

Post by sahmeepee »

krick wrote: post #59
actinium226 wrote: post #57

Earlier quoted context omitted.

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…

You might be interested in this app to try it for yourself:

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.

Re: New laser could cram GPS alternative into a shoebox

#72

Post by rcxdude »

gmrple wrote: post #18
bee_rider wrote: post #11

We’ve had other discussions of these sort of quantum compass ideas, see 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. In…

Gravity map matching is an approach that can provide absolute references, the general problem there is that gravity maps are not good enough.

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.

Re: New laser could cram GPS alternative into a shoebox

#73

Post by rcxdude »

ricksunny wrote: post #34
bee_rider wrote: post #28

Earlier quoted context omitted.

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

Re: New laser could cram GPS alternative into a shoebox

#74

Post by rcxdude »

KennyBlanken wrote: post #7
master_crab wrote: post #2

Sadly, the first applications of this will most likely be military.

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 transmis…

High-grade accelerometers (of any kind) are still subject to export restrictions, especially ones which can handle the G-forces in missiles.

Re: New laser could cram GPS alternative into a shoebox

#75

Post by rcxdude »

littlestymaar wrote: post #13
KennyBlanken wrote: post #7

Earlier quoted context omitted.

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 transmis…

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 th…

They do need very good IMUs though, because of their range and flight time: uncertainty in position increases with both of those.

Re: New laser could cram GPS alternative into a shoebox

#77

Post by cyberax »

ttul wrote: post #51

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.

ICBMs have never relied on GPS. They were always using inertial navigation, sometimes coupled with astronavigation.

Re: New laser could cram GPS alternative into a shoebox

#78

Post by cyberax »

Another obvious idea: use mega-constellations.

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.

Re: New laser could cram GPS alternative into a shoebox

#80

Post by aguaviva »

dgroshev wrote: post #70
aguaviva wrote: post #68

Earlier quoted context omitted.

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 acc…

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…

A high-altitude detonation is not a "World War"

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.

Post reply on HN