Quantum Physicists Found a New, Safer Way to Navigate | Hacker News Reader

Quantum Physicists Found a New, Safer Way to Navigate

wired.com

84 pointsmpweiher29 comments

These quantum compasses are pretty cool, but they are not a GPS replacement. They are a more accurate version of an IMU to use for dead reckoning. They will still drift over time.

I'm guessing that once these are put in production, they will be about 1 order of magnitude better, which is still a significant improvement, but not a "quantum leap" so to speak.

Also, an electronic/physical device that "doesn't drift over time" is a device that hasn't been tested for long enough.

Is it a compass? It sounds to me like they are mapping these magnetic anomalies. If they have a map it should provide an absolute position, not a movement vector to integrate, so no accumulation of error. But they have to map the anomalies.

NOAA did the mapping already, making this like some kind of geoguessr for robots.

I wonder how much those anomalies change over time and how updates would get rolled out without breaking that "unhackable" aspect of it

There's a slew of detail missing.

The "fine detail" magnetic field changes throughout the day (like the tide) and the underlying pattern itself shifts such that a new "map" is issued every five years which is actually a spherical harmonic equation with a depth of 24 (IIRC) terms at least.

(Addendum: degree 12, my bad .. (or degree 790 if you're aiming a missile)

https://en.wikipedia.org/wiki/World_Magnetic_Model or

https://en.wikipedia.org/wiki/International_Geomagnetic_Refe...

choose your model adventure, these are 'coarse' global models with five year epochs, see also:

    The Enhanced Magnetic Model (EMM) is a sister product of the NGDC featuring a much higher amount of data to degree and order 790, giving a wavelength of 51 km as opposed to the 3000 km of WMM.

)

Ideally you also want nine sensors, one for each XYZ axis at three spread out vehicle locations: typically tail + each wing tip on an aircraft to get that mag flux differential across the craft.

It also helps to have ground base station that can record the diurnal flux (daily changes as the earth turns) from a fixed position to subtract from the nine readings on a moving vehicle.

Oh, yeah, heading also plays a role, so you need a Kalman filter formed from a butterfly wing motion pattern in order to subtract the field induced on a the craft by motion that varies with heading.

It's fun stuff.

From what I have read the magnetic mapping it not enough for a position. It needs additional information to limit the possible positions. So the technology could be fairly accurate on a train or car. On a ship or airplane with an imperfect current position and course assumption it may not be very accurate and even drift over time.

They are often called "quantum compasses" although they are complete inertial measurement units which have an accelerometer, magnetometer (a compass is a magnetometer), and a gyroscope.

The subtle parts of the magnetic field of the Earth shift a lot related to the movement of metal through the mantle. NOAA and the DoD periodically create new maps of the magnetic field, but they have a lot of error and noise.

Sure, I’m not saying it is a GPS replacement or anything.

But, a measurement of absolute position is a fundamentally different thing from trying to figure out a position by integrating from an IMU, right? The latter inevitably accumulates errors. The former should not accumulate error. The measurements might be extremely noisy, but noisy and error accumulating are different from a signal processing point of view.

(I think you meant to say "The former should not accumulate error" instead of the latter.)

Good catch, thanks

The magnetometer's reference data is so inaccurate for positioning and shifts so much that error will still accumulate.

Magnetometers have been used in IMUs for over 50 years. Their shortcomings have little to do with the precision of the instrument.

All magnetic compasses are magnetometers, but not all magnetometers are compasses. Some magnetometers output absolute magnetic field strength (scalar) while vector magnetometers output heading and strength of a field.

no one seems to be claiming that it's a GPS replacement. the article specifically calls this out as a check on or a fallback for GPS and that getting accuracy to within 200m would be a huge success.

A quantum leap is actually a tiny event e.g. an electron energy level transition

You’re thinking of a quantum jump. https://www.merriam-webster.com/dictionary/quantum%20leap

They're synonyms, per your link. Also check out Wikipedia

>Quantum Jump

>Redirected from Quantum leap (physics))

https://en.wikipedia.org/wiki/Quantum_leap#In_general

Tiny in absolute terms, but huge relative to the things involved.

Order of magnitude is sufficient to remove reliance on GPS in a lot of military applications. The Russian aggression in Ukraine has shown that a lot of Western precision weapons were rendered ineffective due to GPS jamming.

They say that the magnetic field detectors are intended to be used in conjunction with a detailed 3D map of Earth's magnetic field.

By identifying various kinks (anomalies) in the direction and magnitude of the magnetic field it is possible to identify exact points on the map.

Therefore there is no drift as long as you are not far away from the last identified point.

The only downside is that the magnetic maps need to be brought up-to-date from time to time, due to slow changes in Earth's magnetic field, and only few countries have the resources to keep such magnetic maps up-to-date.

Exact?

See https://news.ycombinator.com/item?id=41188347 and realise that the EMM "high res" map has a wavelength of 50+km .. compare that to, say, old school LORAN positioning accuracy.

Also .. the "coarse" map models (linked in comment) are good for five years, the enhanced models less so .. and there's those other factors.

It's also a wee bit trickier than you might think to (say) fly a route and identify your location only from DTM contour path directly under craft. (Subsitute mag vectors for DTM values)

It's more like old school missile plotting via DTM's where a preprogrammed "follow this" path is generated to facilitate optimal "when the value rises, turn here" instructions .. which are great "recipe navigation" commands .. until something goes wrong, it strays too far off course and has to recover.

Identifying any position via a "random" 50 line km slice is a much harder problem.

Depending on how much more accurate they are than an IMU (mems or gyroscope based) - you might see them have a very real and significant effect in submarine navigation, especially for drones.

> Also, an electronic/physical device that "doesn't drift over time" is a device that hasn't been tested for long enough.

I just want to say that I love this phrase, it reflects my experience perfectly.

>They are a more accurate version of an IMU to use for dead reckoning. They will still drift over time.

A magnetometer is a completely different device than an IMU.

A sensitive enough magnetometer coupled with accurate magnetic maps can act as a GNSS alternative, albeit not as spatially accurate. There's a handful of companies currently working on quantum PNT and magnetic/gravity map matching solutions. I work for one of them.

https://archive.ph/XXCA3

I want to live long enough for the moon to have so much activity it needs its own GPS system.

BTW couldn't they use Starlink and the few other LEO sat networks with thousands of nodes as some kind of augment to GPS (SBAS)

https://en.m.wikipedia.org/wiki/GNSS_augmentation

Most of the downsides of celestial navigation don't exist on the moon, so that might be cheaper and easier for a good while.

Would it give good readings near a major city? A compass is basically useless where I live.

(2018)

Russian pilots are still and must be capable to navigate with the stars.

I don't know about US pilots, but it's still taught to ground people in various places.

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