Journalists get it wrong, again. Sigh. It will never replace GNSS. It's quantum inertial navigation (QIN) that double-integrates acceleration like another method, requiring external position, heading, and velocity (re)calibration and drifts without them. It has absolutely no idea where it is from only itself.
It will have to. That is the point. This isn't about better in-car navigation. The big money behind quantum gyroscopes is the potential to guide submarines/aircraft/missiles in times of war when the GNSS systems are down or otherwise unreliable, just like the best of traditional gyroscopes. Dead reckoning is a legitimate means of navigation, but there are also some aspects where actual replacement of GNSS might happen. An extremely sensitive gyroscope could probably determine latitude based on the earth's rotation (Foucault Pendulum). Then layer on a detailed map of variations in the earth's gravity and/or magnetic fields and one might be able to pinpoint a location absent external signals.
That's an extremely niche application unlikely to be scaled down to anything smaller than a backpack like laser ring gyros. As such, this type of positioning gear isn't for consumer use and is targeted mostly for underground surveying.
Why does it matter if it's not for consumer applications? GNSS is used for many more applications (and arguably more critical) than consumer applications (agriculture, mapping & surveying, aeronautics, shipping, etc.)
Also just want to mention that, yes, integration errors accumulate when using intero-receptive sensors but if errors are small enough (white noise, various biases, sample rates, quantization, etc.) from the inertial sensors an odometry solution might be adequate until an extero-receptive sensor can localize the sensor within an external frame.
This can shift the discussion from solving a problem that has no solution (i.e. how do I integrate a signal with white noise without any error) to an engineering problem (i.e. what error parameters allow the odometry to be accurate within x% over some timeframe).
>The end goals of the TIMU program are the demonstration of a single-chip IMU which maintains an accumulated position error of less than 1 nmi/hour with device volume of less than 10 mm3 and power consumption of less than 200 mW.
(My job is related to estimating location of things).
Yes, for their relevant applications. If you were a commercial spelunker or were the Ukrainian army needing to lob missiles into Russia that were impervious to encrypted GPS jamming, then you would gladly welcome your quantum overlords. Neither LRG or QG are ever going to be made into MEMS devices shoved into an iPhone. Its application is dead reckoning. For the use-case of navigation underground useable by everyday people, Skyhook-like services that rely on 5G UWB microcells are the most likely evolution beyond relying on Wi-Fi SSIDs and conventional cell towers for tower-assisted GNSS.
> It has absolutely no idea where it is from only itself.
Neither do GNSS satellites. You can't solve this problem with any method without giving each device a starting reference, and then either continually updating it or enabling some mechanism for multiple devices to vote/agree on reference(T+1).
This new tech might allow other improvements, such as the QIN device being a relatively-static "hub", and the user wearing smaller, cheaper accelerometers that connect to it regularly to reset their starting positions.
Yes, satellites are tracked by ground stations, and receive an update every 24 hours with information about their project positions in the future.
GPS satellites transmit this data in the form of an almanac which includes all the high level parameters for estimating the location of every satellite, and ephemeris data which allows you to calculate the precise location of the satellite, when used in tandem with the almanac.
The almanac doesn’t change too often, but ephemeris data is only valid for a few hours. The satellites recalculate the ephemeris data themselves, and normally have a few months of needed data stored on board, just in case they can’t get updates. But the expectation is they’re updated every 24 hours.
This is also why, in a zombie apocalypse type scenario, GPS would become inaccurate past the point of usability within a few weeks, maybe a few months max.
Amongst other things, the clocks need to be corrected for relativistic effects.
Due to the net effect of both kinetic and gravitational time dilation, clocks onboard a satellite advance more quickly than they would on Earth (when observed from Earth).
They use atomic clocks, so it's accurate to something like 1 part in 10^16, or about 1 second in a billion years! A friend of mine is working on the next generation, which will be even more accurate.
In contrast, the force of gravity experienced by the satellite is known to much less accuracy. In fact, changes on a monthly basis due to rainfall/rivers and tides. The GRACE satellites measure the change, although I couldn't find any information on how accurate their measurements are, except that they can measure the distance between the two satellites to within a micrometer (10^-6), so substantially less precision than the clock!
Not quite that accurate. Apparently it’s more like 3 seconds per million years for a rubidium atomic clock, and 1 second per 3 million years for a hydrogen maser. (Caesium atomic clocks are somewhere in between)
Because it can't. There are always cumulative errors in INS. There is no way around this without external references, but then it's no longer inertial navigation and it's inertial-assisted navigation.
An underground navigation system based on triangulation of UWB cells would be a better solution than some nonstarter project the size of a refrigerator that requires liquid nitrogen.
There is no liquid nitrogen involved here. The instrument from the article is actually rather big, current generations of quantum IMUs are roughly half this size with lots of room for miniaturization.
One big advantage of these atom interferometers is that they actually don't need to be recalibrated because the reference is the wavelength of the lasers which can be controlled with extreme precision.
A big disadvantage is however the limited repetition rate, which is on the order of only 1 Hz at the moment. Currently, combinations with "classical" IMUs seem most promising, and there is lots of interest in these devices for applications in planes, cars and spacecraft.
Actually, in a train context, inertial is pretty damn high accuracy because you already have the world's best odometer showing (A) how many times your known size wheel has turned on your known track; and (B) you can test many axels simultaneously to ensure no slippage (I guess you wouldn't test the wheels as they move faster creating a higher frequency sampling requirement for ~no benefit whereas a dedicated axel feature could live within an environmental enclosure protected from dust and grime); (C) you are constantly doing exactly the same trip-segments over and over again.
So for a train with an offline positioning requirement, I'd suggest that an odometer based solution is close to ideal.
Re odometer - don't the wheels of a train slide a little bit? I know the train is big pile of heavy iron, but still. My naive thinking is that when braking or during a rush start some extra distance can be covered.
If you are averaging axels across multiple carriages slippage is unlikely to amount to much. Moreover, because you are traveling known segments, you can reset your position at each station or known intersection/detectable segment terminus, so you're going to have zero accrued drift at that point. It's a perfect deployment scenario for an odometer based solution. If you want to be higher confidence, sensor-fusion with an IMU, laser TOF/LIDAR, camera, ambient light sensor, radio signals, or MEMS microphone can verify position. Et voila! - no need for GNSS.
Generally trains do everything they can to avoid slipping. They have anti-lock breaks and traction control just like your car, and stuff your car doesn’t have, like “sanders” which pour sand onto the track just in front of the wheels.
Regardless of material, dynamic friction is always lower than static friction. So for maximum acceleration and breaking it’s important to ensure you wheels stay in “rolling” mode of interaction, and don’t slip.
Is that necessarily true of this quantum thing? I know nothing about it except this article, theoretically if it kept track of exact Plank lengths or something, then there would be no errors to accumulate, right? Lots of the things that seem intuitively true break down in weird ways when dealing with quantum effects.
TL;DR-TL;DR: says the opposite of your implied claim, "atom-gyros are set to outperform light-based gyros"
TL;DR: this is a StackExchange question with 1 answer, noting it is indeterminate if a quantum gyroscope would be more accurate than a laser-atom-based one.
It looks like you rushed through and missed that in this context, TFA is describing an atom gyro.
That leaves conversation at a point where either A) we assume the scientist interviewed knows what they're doing, or B) following your unstated lead, assume they're a crackpot and the whole article is irrelevant because they're untrustworthy, and thus in an ideal world, there's 0 comments on the article.
All accelerometers tell you is the direction of the acceleration vector (ie how speed is changing and in which direction). You still have to add the individual vectors to derive where you actually are.
And if you don't sample fast enough and your acceleration has frequency components at frequency comparable to your sampling, the acceleration you measure may not reflect where you actually are (ref Nyquist sampling theorem)
Imagine sampling at 1hz, and you just happen to have a bump every 1 sec (eg your wheel happens to have a flat spot and is turning at 1Hz), followed almost instantly later by a bump in the opposite direction. Your sampling only sees (say) the +ve components, misses the -ve and accrues a bunch of error.
If you can sample fast enough, you can minimize this sort of error, but you can't really make it go away.
Oh, btw, if you make it work well enough you're considered munitions for export control purposes, so limits the number of countries you can sell to. Same reason civilian GPS units stop working somewhere around 1200mph
These are all excellent elucidations of classic mechanical principles making it hard. I'm not sure they're enough to make me say the scientist/institution in the article a priori has it wrong, especially because it's not a one-off dude just messing around.
I've been looking for some data on estimated drift from this, but no specifics. That said, since it's looking at wave properties of cooled atoms, I'm assuming we're talking "wavelength" accuracy as opposed to more conventional inertial nav systems.
My point perhaps is that though this is "nothing new", it's (probably) way more accurate than anything before it. So the "pain points" of recalibration and drift are extremely minimized.
So it doesn't solve the issue inherent will all inertial navigation approaches (error accumulates very quickly because of the double integration), it just has less error?
Reading the article, I was under the impression that this was to be used for stuff like submarines, or vehicles in the arctic... stuff where finding one's position might be tricky.
This is absolutely overkill for a train where you can just rely on a calibrated odometer to know your position.
Not to mention wireless networks like the ones for the airtag or the wifi endpoints mapping google has could be adapted to share positions of "right here, right now" anonymously.
Which means that if only one device knows where it is, you can calibrate, and if several know, you can even correct for mistakes.
If the system is precise enough, you only need to calibrate once in a while. Being at home/office, on the local wifi, once, could be enough.
Besides, nobody wants the GPS to go, but it's a nice alternative that can't be jammed by enemy forces and can be used for hiking, diving, etc.
I mean the exact position, down to a millimeter, when e.g. a photo sensor on a train passes past a LED mounted below the station platform. The LED's light is modulated so there can be no mistake, and its location is precisely known.
A meter precision is fine for what most people use GPS for. If the device is as precise as they say, you won't add much imprecision to the original calibration, so you will be in the right tunnel at the right time.
