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Celestial Navigation for Drones

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Re: Celestial Navigation for Drones

#91

Post by Animats »

adolph wrote: post #4

I wonder if GPS and the like will be used more for their clock features than for position. The emissions celestial bodies are perfect fiducial markers [0,1], but connecting them to position still requires accurate timekeeping [2], as the paper notes: Provided the use of an accurate clock, the results presented in this paper will not degrade over time. 0. https://www.twz.com/17207/sr-71s-r2-d2-could-be-the-key-to-w...…

The clock accuracy required for celestial navigation is on the order of seconds, not microseconds.

Re: Celestial Navigation for Drones

#92

Post by jcims »

BenjiWiebe wrote: post #72
jcims wrote: post #28

Earlier quoted context omitted.

That's a great idea. In the earlier days when they had about 2500 satellites in LEO I built a small visualizer from the fleet TLE data and it was remarkably simple with the skyfield library. If you're in the fringes of a GNSS denial area ADSB might be useful as well. Would need more hardware of course.

Doesn't ADS-B get the location from GNSS?

Yes it does, but unless we’re talking an entire system failue the GNSS denial does tend to have limits in range. I’ve picked up ADSB traffic from well over 200km with a simple ground antenna, so if you’re in the fringes in could be a useful additional signal for similar reasons to the satellites.

Just spitballing though really.

Re: Celestial Navigation for Drones

#93

Post by magicalhippo »

sandworm101 wrote: post #80
alexpotato wrote: post #34

Earlier quoted context omitted.

Reminds me of the "the distance between the rails of a railway are due to the width of Roman horse drawn carts" story.

Lookup why torpedo's are almost universally 21" in diameter. The short version: because that was how big they were last time. There is no reason beyond 21" being usrd once upon a time and nobody wanting to break from it and have the old torpedos not work in the new boats.

H I Sutton, a naval defense analyst, made a nice video on this topic.

[1]: https://www.youtube.com/watch?v=cuS0yhwSPMc

Re: Celestial Navigation for Drones

#94

Post by anovikov »

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 small camera and are visible whole night.

Re: Celestial Navigation for Drones

#95

Post by nuccy »

anovikov wrote: post #94

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…

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 known time to find your location, with satellites it is much much more complicated: you need to know where the sun is, you need few images of a satellite or even a video (likely on top of image of stars anyway) to distinguish it from the stars and to solve the trajectory.

1. https://en.m.wikipedia.org/wiki/Proper_motion

Re: Celestial Navigation for Drones

#96

Post by m2fkxy »

anovikov wrote: post #94

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.

Re: Celestial Navigation for Drones

#97

Post by joshvm »

mpetroff wrote: post #67
joshvm wrote: post #46

Earlier quoted context omitted.

It would work on the ground, I believe the pilots (normally) had to get a fix before takeoff. You do need to see the sky without cloud cover, but spy satellites were less of a concern back then so less risk of being overflown during a daylight setup. The cameras are basically visible telescopes with very narrow fields of view and good baffling. Only a few stars are bright enough that you can sight off them, but it ca…

BICEP3 actually uses a >20 year old CCD camera with analog video output (BICEP Array uses newer cameras, with more modern sensors). Daytime star pointings are possible by using a low-pass filter to block visible light and take advantage of the sensitivity of CCD / CMOS sensors to the near infrared, where the daytime sky is more transparent, combined with baffling.

I would add it also uses an ancient analog TV for manual sighting in combination with the GUI for semi-auto centroiding. I always thought that was funny to see, but it seems to work well enough. Also, inserting that baffle is somewhat terrifying because it slots into a hole next to the main vacuum window and if you dropped it on the membrane, bad things would happen. Always fun to bump into Polies here :)

Re: Celestial Navigation for Drones

#98

Post by littlestymaar »

Havoc wrote: 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?

Re: Celestial Navigation for Drones

#99

Post by joshvm »

gunian wrote: post #75
mpetroff wrote: post #67

Earlier quoted context omitted.

BICEP3 actually uses a >20 year old CCD camera with analog video output (BICEP Array uses newer cameras, with more modern sensors). Daytime star pointings are possible by using a low-pass filter to block visible light and take advantage of the sensitivity of CCD / CMOS sensors to the near infrared, where the daytime sky is more transparent, combined with baffling.

how hard would this be to set up for a total hardware noob? and how good or useful would the data be? i know gaia data for instance is available for free but if one used just a homemade telescope could any useful celestial data be acquired?

It depends what you mean by useful. On its own, all you're doing is taking pictures of the sky and figuring out where the camera was pointing (and its field of view). Where it's useful is calibrating the pointing direction of other systems. It's fun to try the software at home (there is a public web interface), you just need a camera that can take long enough exposures to see stars without too much noise.

One of the more "useful" backyard astronomy tasks that is achievable for a dedicated amateur is variable star observation (eg AAVSO), because many stars don't need huge telescopes to observe and it's very expensive for a big observatory to stare at a single patch of sky for weeks. Nowadays we have instruments like LSST which is basically designed for this sort of surveying, but public data are still useful. And you do need to know exactly where you're pointing, so either you do this manually by pointing at a bunch of target stars, or you can use a guide scope that solves the field for you.

Re: Celestial Navigation for Drones

#100

Post by anovikov »

nuccy wrote: post #95
anovikov wrote: post #94

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…

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 image and find satellites within a circle where each of them might be, starting with the slowest moving - furthest away from you - ones (they provide poorest precision of coordinates because parallax is small, but you need to start with something, but their search circle will also be smaller), locating those, you get better coordinates of yours and the search circle for each satellite becomes smaller, then you can find faster moving satellites too to get precise coordinates of yourself.

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