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Celestial Navigation for Drones

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Re: Celestial Navigation for Drones

#101
post #81
post #36

Earlier quoted context omitted.

That. However that works just fine for ICBMs and the like… The future is more likely to be quantum accelerometers and quantum gyroscopes, as they have no “external dependency”.

More likely image-based navigation, where you just upload the entire imagery of the route and then use it to correct your inertial references. Encrypted positioning information from low-orbit satellites is another option.

That doesn't work well in some conditions, it's not new either. Some cruise missiles that have TFR (Terrain-following radar) and actually do this already.

It also is not really applicable when you are on a balistic course at *very* high altitude, course correction has to happen early in these case given the reentry speed/constraints.

Re: Celestial Navigation for Drones

#102
post #60

Earlier quoted context omitted.

I mean, considering celestial navigation was a thing long before we had accurate clocks… I’d venture they aren’t wrong at all. Or did you forget that people have been doing celestial navigation by hand for over two millennia?

Celestial navigation actually drove the development of accurate clocks https://timeandnavigation.si.edu/navigating-at-sea/longitude... Quartz clocks didn't overtake chronometers in terms of accuracy until the mid 20th century, and chronometers will still beat regular crystals like you'd find in cheap electronics.

> Celestial navigation actually drove the development of accurate clocks

That's true, but that still doesn't change the fact that you don't need nanosecond precision for this purpose. At the equator, 1 second precision gives you roughly 500m accuracy, which is already much higher than what the celestial imagery allows here (4km in the paper).

Clearly this method isn't limited by clock accuracy at all.

Re: Celestial Navigation for Drones

#103
post #87

400 Bucks Sensors is a touch rough. This would only work at night, right?

The full title is: > An Algorithm for Affordable Vision-Based GNSS-Denied Strapdown Celestial Navigation Emphasis mine. In what kind of context do you expect drones to operate in an area where GNSS is disabled by electronic warfare devices? Do you really think that a $400 cost is of any issue for military use?

> Do you really think that a $400 cost is of any issue for military use?

If your name is Ukraine then yeah. Effectively halves the number of drones you can build

Re: Celestial Navigation for Drones

#104
Here's the camera used.[1]

It's not exotic. It's a 1936 × 1216 Sony sensor with a C-mount lens. That's below current phone camera resolution. It's monochrome, which makes sense in this application.

They have bigger collecting optics than a phone, and you get better sensitivity without the color filters.

I'm not clear on how they get their "down" reference. It's clear how they get heading; that's easy if you can see the stars. But you need an accurate horizon or vertical to get latitude and longitude. One degree of error in the vertical is maybe 100 km of error in position. How good are drone AHRS systems today in attitude? They have a correction system that works if you fly in a circle, but that just corrects for constant misalignment between camera and down reference.

[1] https://www.alliedvision.com/fileadmin/pdf/en/Alvium_1800_U-...

Re: Celestial Navigation for Drones

#105
post #103

Earlier quoted context omitted.

The full title is: > An Algorithm for Affordable Vision-Based GNSS-Denied Strapdown Celestial Navigation Emphasis mine. In what kind of context do you expect drones to operate in an area where GNSS is disabled by electronic warfare devices? Do you really think that a $400 cost is of any issue for military use?

> Do you really think that a $400 cost is of any issue for military use? If your name is Ukraine then yeah. Effectively halves the number of drones you can build

> Effectively halves the number of drones you can build

You're confusing the price tag of an FPV drone (for which this tech has no use, 4km precision is roughly the range of such drone, so even without a positioning device you'd get such a precision…) with the one of a long-range drone which is hundreds of magnitudes larger, even for Ukrainians.

Re: Celestial Navigation for Drones

#106
post #96

An idea: use satellites for navigation. No, not the satellite signals, but the satellites themselves. Use NORAD orbital elements data for satellites to deduce land coordinates using time and pixel coordinates of satellites observed. Low orbit satellites will be only observable for two hours or so after sunset and before sunrise, but there are enough medium Earth orbit satellites that are still bright enough for a sma…

yeah, and then you need to get refreshed orbital elements for those satellites. not good if you are in an airtight environment. celestial ephemerides don't change nearly as much.

No problem, in a few hours orbits of satellites don't change much, a day or two days' old ephemeris are ok. Especially not those on medium earth orbits which are the ones to be used (geostationary and other high orbital ones are too dim + too far away to provide precise coordinates; low orbit ones are not visible most of the night)

Re: Celestial Navigation for Drones

#107
post #95

Earlier quoted context omitted.

If you see satellites then likely you see even more stars. Unlike satellites the stars barelly move (actually they do, see "proper motion" [1]) relatively to each other, so a catalogue of stars (two coordinates values and two proper motion values) along with the time of observation is sufficient to be used over decades, unlike NORAD orbit elements requiring regular updates. With stars you need just one image at a kno…

How do you find your location from one image of stars? It is possible if you have a precise vertical but you don't have a precise vertical on a moving UAV. That is, you need an inertial system on top that will provide you with a vertical. With satellite images, you don't need anything apart from time. And no, you don't need to "make a video to see satellites move", you start with your approximate location, make an im…

You are right: to find a location from a star image you need a true horizon, but unless UAV is pulling some Gs even a basic accelerometer would give you the horizon, accuracy of that estimation will limit the accuracy of your location.

Regarding satellites: so "starting with the slowest moving" requires a series of images, doesn't it? Then how do you know "your approximate location"? From stars? In theory I understand what you say but practically it would be much more complicated and the obtained accuracy would not be better than with the stars, since in either case you also need a horizon to know your location.

Re: Celestial Navigation for Drones

#108
post #107

Earlier quoted context omitted.

How do you find your location from one image of stars? It is possible if you have a precise vertical but you don't have a precise vertical on a moving UAV. That is, you need an inertial system on top that will provide you with a vertical. With satellite images, you don't need anything apart from time. And no, you don't need to "make a video to see satellites move", you start with your approximate location, make an im…

You are right: to find a location from a star image you need a true horizon, but unless UAV is pulling some Gs even a basic accelerometer would give you the horizon, accuracy of that estimation will limit the accuracy of your location. Regarding satellites: so "starting with the slowest moving" requires a series of images, doesn't it? Then how do you know "your approximate location"? From stars? In theory I understan…

No you just "start looking" on a single image.

Know your approximate location: by dead reckoning. You will need coordinate fixes once every few minutes anyway and you know your direction precisely enough from the same stars, error only comes from wind direction not being precisely known. So we are speaking of correcting for at most tens of kilometers of error. 10km at a typical distance of 1000km to a low orbit sat is Astrometry allows for locating objects down to about 0.2 pixel reliably and to 0.1 pixels in optimal conditions, so a typical wide-angle camera that might have about 40 arcsecond pixels will easily give 8 arcsecond precision, for a satellite 4000km away (about 2000km orbit at 30 degrees elevation), that's 170 meters of location error, which is more than good enough for navigation (final targeting is done by optical pattern recognition on the ground anyway).

>since in either case you also need a horizon to know your location.

No you don't. Benefit of using satellites is that the source of coordinate data is the parallax of satellites vs stars. It works without having a vertical/horizon.

Simply put, we calculate that in a predicted location the satellite will be at a certain pixel distance from a few of the closest stars on the photo. And it will be a few pixels off that predicted point. Distance and direction of that error allows for calculation of discrepancy of predicted vs real location (and repeating this process on several satellites visible on same photo, allows to decrease the error by removing outliers - which might be noise/space rays on images or errors in star catalogs or orbital elements data, or satellites changing their orbits - and averaging the results).

Re: Celestial Navigation for Drones

#109

Ctrl+F and 0 results for munitions or bombs. Seems like this is really about $25 controller gets drones to within 4km in GPS denied enviroments, after which a $50 infrared camera + DSMAC find targets to hit.

Don't get distracted https://news.ycombinator.com/item?id=42388354

note: i used gpt to clean this up because i am ill and distracted by snowfall and cold. It muddied some of my points, but it removed a lot of PII and rambling. note over.

I noticed some commenters questioning details in the article, like the Wi-Fi triangulation and the earthquake survivor detector. While it's fair to discuss technical aspects, I believe the focus should be on the broader implications rather than dismissing the story based on perceived inconsistencies.

I haven’t dealt with clearances or compartmentalization in years, but I know how serious these matters are. Disclosing specific names, dates, or events carries severe consequences—this isn’t something covered by toothless NDAs. The penalties can include federal prison for treason. I’ve personally experienced the DoD investigating me just because I was listed as a reference. It’s an intimidating process, and it makes sense why people who fear being doxxed rewrite their stories, swapping out modular details to obscure sensitive information.

Regarding the Wi-Fi triangulation: this is well within the realm of possibility. Many years ago, I purchased a Hydra SDR radio with inexpensive RTL-SDR chips. With four matched antennas arranged in a line or an X, connected to a Raspberry Pi 4, I could triangulate signals and visualize the results on a map. The hardware wasn’t advanced, but it worked. Even in 2012, there were rumors about using Wi-Fi signals to see through walls. Whether or not the article is perfectly accurate, the point is to consider the ethical and societal consequences of such technologies, not to nitpick technical details.

As for the earthquake survivor detector, the underlying principle is related. Identifying survivors using leaked signals like Bluetooth or cellular emissions isn’t fundamentally different from using Wi-Fi for similar purposes. The scenarios may involve different actors—military versus contractors—but the capabilities are converging.

I’ve worked at a defense contractor that manufactured components for Boeing and McDonnell Douglas jets. While I avoided involvement with military projects, I know how extensive and layered the contractor ecosystem is. Comments suggesting "there are only a few" don’t align with my experience.

On a personal note, I’ve always struggled with the ethical implications of the work I’ve done. This has made my career difficult. I don’t judge others who take these roles—someone else will do the work if they don’t—but my own scruples have been a constant challenge. For example, I once worked on a project at a large entertainment company based on an idea I had years earlier. The demanded i eventually sit in the office and handle tier 3 phone calls. I had a minor breakdown in the stairwell; i didn't even let my children consume their content, but i was too jazzed to work on the thing that i pitched to apple 7 years earlier. That was over a decade ago, but i'm still annoyed at myself.

I believe stories like this should be taken seriously. Dismissing them based on perceived inconsistencies seems like rationalization, to me.

thanks for the link!

Re: Celestial Navigation for Drones

#110
post #5

Perhaps I am too paranoid, but I've been told to avoid doing any DIY in this field of study. Apparently, or so I'm told, out of the many, many ways to end up on a list — building a working celestial navigation system can lead to some very inconvenient outcomes. Second, only to ordering large quantities of certain chemicals online. Is this true? ——— EDIT - from the paper, this is incorrect, > The introduction of GPS c…

Not NSA - you'd have someone from US Bureau of Industry and Security tracking you down (no pun) for most likely violating export controls if you were to openly share information on building the technology. Celestial tracking is a dual use technology (See 7A004 or 7A104) - https://www.bis.doc.gov/index.php/documents/regulations-docs...

Openly publishing information in e.g. a book (or presumably a website) does not count as exporting. Releasing software is a bit more hazy, but has been defended[1].

[1]: https://en.wikipedia.org/wiki/Pretty_Good_Privacy#Criminal_i...

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