[HN Gopher] Celestial Navigation for Drones
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Celestial Navigation for Drones
Author : throw0101b
Score : 128 points
Date : 2025-01-20 12:02 UTC (10 hours ago)
(HTM) web link (www.mdpi.com)
(TXT) w3m dump (www.mdpi.com)
| jcims wrote:
| I didn't see an explanation of what strapdown meant in this
| context, so I dug one up:
|
| "Traditional, stable-platform navigation systems commonly involve
| separate accelerators and fibers or laser-based gyroscopes, with
| all the components mechanically and rigidly mounted on a stable
| platform that is isolated from the moving vehicle. This leads to
| the drawbacks of large size, poor reliability, and high cost. In
| contrast, in strapdown navigation systems, the inertial sensors
| are fastened directly to the vehicle's body, which means the
| sensors rotate together with the vehicle. "
|
| https://www.mdpi.com/2504-446X/8/11/652
| plasticchris wrote:
| Or in short, the sensors are strapped down to the platform
| being measured - like your phone's sensors for example.
| boscillator wrote:
| Yes! It's in contrast to gimbaled systems. Putting the
| measuring instrument on a gimbal simplifies the math and
| often improves accuracy, but at the expense that you need
| this large moving object that needs more power.
| imglorp wrote:
| Gyros on gimbals have other drawbacks, such as drifting and
| gimbal lock.
| UltraSane wrote:
| The ultimate example of this is the incredibly accurate and
| expensive and complicated floating Advanced Inertial
| Reference Sphere used on the Peacekeeper ICBM.
|
| https://en.wikipedia.org/wiki/Advanced_Inertial_Reference_S
| p...
| adolph wrote:
| 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...
|
| 1. https://timeandnavigation.si.edu/multimedia-
| asset/nortronics...
|
| 2. https://www.rmg.co.uk/stories/topics/harrisons-clocks-
| longit...
| KineticLensman wrote:
| They are perfect markers only as long as you can see them.
| Clouds and fog are your enemies here
| mpenet wrote:
| 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".
| all2 wrote:
| I presume radio signal or certain frequencies of thermal
| would be viable for adverse weather conditions.
| rich_sasha wrote:
| I guess timekeeping is relatively easy? These systems would
| only operate independently for a few hours tops. I would
| imagine even a standard quartz movement would be accurate
| enough.
| GJim wrote:
| > I guess timekeeping is relatively easy...... would imagine
| even a standard quartz movement would be accurate enough.
|
| Good Lord! How wrong can you get!
|
| Very precise timing (often taken from GNSS for convenience)
| is needed for much of the modern word, from IP, cellular and
| DAB networks, to AC phase matching the electrical mains grid.
| Quartz clocks are nowhere near accurate enough for these
| purposes.
|
| This government report makes very sobering reading:
| https://www.gov.uk/government/publications/satellite-
| derived...
|
| TLDR: Our dependence on GNSS for timing almost dwarfs that
| for navigation. And we urgently need to consider using
| backups (be that local atomic clocks, or long wave time
| signals).
| withinboredom wrote:
| 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?
| jjk166 wrote:
| 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.
| rich_sasha wrote:
| In the context of position keeping I think it's not too
| bad.
|
| If we focus on longitude, where timing I guess matters
| more, the equator moves at a speed of about 0.46 km/s. So I
| guess being out by 1 second translates to precisely 0.46km
| error. That's second order compared to the stated error of
| 4 km, and it will be smaller still away from the equator.
|
| I'm working off the assumption that such a drone can sync
| up to an accurate time source at launch, and then only
| needs maintain good timekeeping for its time in the air. I
| guess without the accurate initial time source, it gets
| bad. Being a minute out is suddenly 30km of latitude
| direction away.
| fisherjeff wrote:
| Plus I think most decent quartz oscillators have a drift
| measured in single-digit PPM (or less) so even 100ms
| error over a single sortie would be surprising.
| withinboredom wrote:
| > Our dependence on GNSS for timing almost dwarfs that for
| navigation.
|
| Galileo satellites also now sign the timestamp (IIRC) via a
| Merkle tree so you know it isn't spoofed.
| jenny91 wrote:
| Depends on what you're using time for. If you are doing
| advanced anti-jamming for comms for instance, you want
| extremely accurate timing (more accurate means you can
| frequency hop faster and do better anti-jamming).
| areoform wrote:
| 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 caused the interest in celestial
| navigation to wither due to its relative inaccuracy.
| Consequently, celestial navigation is primarily seen only in
| space-based systems, whose orientation must be known to high
| levels of precision. Nonetheless, celestial navigation was
| identified as a desirable alternative to GPS [2], primarily due
| its robustness against potential jamming. Critically, few GPS-
| denied alternatives exist that are capable of using passive
| sensors to estimate global position at night or over the ocean.
| For this reason, celestial navigation remains an important topic
| of research.
|
| The US and other militaries never stopped using these systems.
| They just stopped talking about them as much. Here's a literature
| search showing some of the slow & steady research on the topic,
|
| https://scholar.google.com/scholar?q=astro-inertial+navigati...
|
| Example systems that have been deployed in many (most? all???)
| American combat aircraft,
|
| https://theaviationist.com/2021/09/10/lets-have-another-look...
|
| https://www.gpsworld.com/honeywell-demonstrates-military-gra...
|
| https://ieeexplore.ieee.org/document/290940
|
| Alright. I'm ready to be on that list, Mr NSA agent.
| wolfram74 wrote:
| I've also been told learning too much about linux or the
| nuclear reactions in power plants or bombs puts you on a list.
| I just assume I'm on several.
| munchler wrote:
| Learning too much about Linux puts you on a list? That can't
| be a thing. Isn't Linux itself entirely a civilian project?
| wolfram74 wrote:
| The rationale mentioned was it was under the subheading of
| people interested in strong encryption, people who care
| about being unobservable might have something to hide.
| Maybe it's a good list? People who you might want to ramp
| up a new Bletchley Park? Probably not.
| Theodores wrote:
| Whatever you do, don't broadcast on the airwaves, as in
| pirate radio. That really does put you on the list.
|
| I don't believe they have the people to monitor those that
| know 'how to use grep' and put them on a list. It stands to
| no reason, government civil servants are rarely from the top
| drawer.
| pvg wrote:
| You're definitely on the list of people worried about being on
| lists now.
| areoform wrote:
| But that's the bestest list!
| RandomBacon wrote:
| The only people not on any lists, are boring people.
| y33t wrote:
| They're just kept on the list of all people not on a list.
| gessha wrote:
| Peaceful, not harmless.
| biofox wrote:
| You will likely raise a flag somewhere if you publicise what
| you are doing, but I highly doubt there would be any issues if
| you're working on this in private as a hobby.
|
| As for chemicals, I can personally vouch that it is a terrible
| idea to order reagents (or even chemistry equipment) as an
| individual. I tried to teach myself organic synthesis in the
| summer before starting my doctoral studies, and ended up with
| MIB searching my house. Certainly on a list now :(
| the__alchemist wrote:
| LLC or nonprofit, with a business address. At least for bio
| reagants, they won't ship to you otherwise.
| 7thpower wrote:
| Please tell me there is a blog post or something documenting
| this experience. Sounds like a fun read.
| biofox wrote:
| Afraid not. I don't have much of an online presence, so
| didn't think to write anything.
| amarcheschi wrote:
| there's always a first time :)
| mavamaarten wrote:
| I remember watching a video about a dude who was building a
| mothership-launched glide drone that could land using
| camera vision. The idea was something like "the highest egg
| drop" or something like that. He was speaking with
| academics about his idea, who quickly told him to stop
| whatever he was doing because that would effectively be a
| forbidden military device. Guided artillery, basically.
|
| Sadly I don't remember who it was, it was a fun story. I
| thought it was maybe Mark Rober or Joe Barnard but I really
| can't find it anymore.
|
| Edit: found it! It was launched from a weather balloon, and
| it was both Mark and Joe. https://youtu.be/BYVZh5kqaFg
| Rallen89 wrote:
| Happened to codyslab, videos taken down now (but still on
| archive.org) of a uranium purification process and
| possibly nilered,no way to prove it but he had a 'making
| rocket fuels: part 1' that was never followed p on. Not
| totally sure though as people like BPS space on yt have
| some pretty in depth tutorials on solid rocket motors
| (does explicitly censor how to make the ignition
| component)
| myself248 wrote:
| Years ago, an acquaintance developed an autonomous flight
| controller for "real" helicopters. Cyclic-collective-tailrotor
| types. It would work on a full-size cargo helo just as well as
| an R/C model. He released it online, because why not? Drones
| are cool.
|
| Some very nice gentlemen showed up and explained that he
| couldn't do that. He didn't get in any actual trouble that I'm
| aware of, but they "asked" him to take down the published code,
| and definitely not fix any of the bugs it had.
|
| So, yeah, you're not wrong.
|
| There are nuances to the rules, involving things that're openly
| published online, but I don't understand it in the least. A
| hacker's guide to ITAR would be an interesting document indeed.
| notahacker wrote:
| > A hacker's guide to ITAR would be an interesting document
| indeed.
|
| I suspect producing something called "a hacker's guide to
| ITAR" really would get you put on a list...
| hnuser123456 wrote:
| I'm sure there are thousands of datasets of the night sky, and
| a camera, gyrometer (to get camera angles), clock, and basic
| image recognition/pattern matching is all you'd need.
| notahacker wrote:
| yeah. Celestial navigation is a pretty standard thing to
| study if you're planning on taking up sailing or learning
| about satellite positioning. Celestial navigation with drones
| raises more _interesting_ possibilities, but I don 't think
| defence of key strategic assets against drones relies on the
| possibility it might be too difficult a problem to solve, and
| there are commercial solutions in the "drone navigation for
| GNSS denied environments" space. Don't even think the people
| that jailbreak consumer drones specifically to remove the
| geofences that prevent them flying near restricted areas get
| into trouble, at least not until someone spots them flying at
| the end of a runway or outside a military base.
| avs733 wrote:
| Can't find a source at the moment but cool side anecdote to
| this...working from memory
|
| Honeywell was largely the driving force behind developing
| terrain avoidance systems for commercial aircraft. Those
| initial systems worked based on comparing the terrain below to
| the flight profile of an aircraft using a radar altimeter.
|
| There was a CFIT (controlled flight into terrain) accident (I
| want to say AA in Peru?) where the mountains basically got to
| tall to fast to give the crew sufficient time to react because
| of that system. That caused Honeyweell to go back and look at
| ways to improve the system to be predictive rather than
| reactive - using a terrain database.
|
| Honeywell bought/came into posession of a russian world wide
| terrain altitude database to do the first generation of this. I
| can only imagine the US had the same thing, or more accurate,
| but this was far enough ago that US Government wasn't sharing.
| areoform wrote:
| You're right! I actually know about the system you're talking
| about! The US data was classified and Donald Bateman, the
| engineer behind this and bought the data post Soviet Union
| collapse.
|
| https://en.wikipedia.org/wiki/C._Donald_Bateman
|
| https://www.flightsafetyaustralia.com/2023/05/don-bateman-
| en...
| avs733 wrote:
| the amount of random 'stuff' like this that I've
| accummulated over the years could fill a book that is
| interesting only to me lol
|
| Thanks for the link!
| hnthrow90348765 wrote:
| I'm told quantum navigation is the new hotness for being on
| lists these days
| Onavo wrote:
| These days celestial navigation is trivial. See my comment here
|
| https://news.ycombinator.com/item?id=42695079
| clarkmoody wrote:
| Plenty of homework assignments in graduate level aerospace
| engineering courses that are right up the alley of this paper.
| Star trackers as backup for GNSS would be of great interest to
| maritime vessels worried about spoofing. So there are plenty of
| non-military use cases for these algorithms.
| maxglute wrote:
| 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.
| the__alchemist wrote:
| I would assume the same. Operation in GNSS-denied environments
| is critical for military navigation systems. Comparatively, for
| civilian uses, it's an addon that provides low accuracy, and
| potentially high development or equipment cost (Maybe not for a
| cel nav camera, but for Ring Laser Gyro INSs etc)
|
| GNSS is very accurate, and receivers are cheap, but its reliant
| on satellite signals makes relying on it a liability in
| adversarial uses.
|
| Cel nav isn't self-contained in the way an INS is, because you
| need a clear LOS to the stars. But, it's useful on a clear
| night when your GPS is jammed.
| mapt wrote:
| Thanks for the summary.
|
| I suspect you could get this to FAR higher accuracy if you
| combined it with a recent upload of Starlink et al LEO
| constellation ephemera, an initial GPS fix at launch, and a
| planned flight path, because LEO constellations are bright
| foreground objects (high location-specific parallax differences
| against background stars) at apparent magnitude of about 5.0.
|
| This is simultaneously not reliant on perfect vertical attitude
| sensing coming off the autopilot IMU, you can do it purely
| photometrically.
|
| The limitation is that this is a dawn/dusk thing, in the middle
| of the night there isn't a ton of light reflected and in the
| day you're limited by scattered daylight.
|
| EDIT: Medium orbit satellites outside Earth's umbra but within
| view still provide some sort of visual fix. I wonder what the
| math is like for the GSO belt at midnight?
|
| EDIT2: Or the Moon.
| jcims wrote:
| 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.
| BenjiWiebe wrote:
| Doesn't ADS-B get the location from GNSS?
| maxglute wrote:
| IMO could synergize well for higher end celestia navigation -
| there are optics sensors for day time tracking, but daylight
| sensitivity is limitation, perhaps much less so when fixed to
| starlink. So maybe feasible $$$ hardware can make daylight
| celestial starlink navigation workable.
|
| Bringing component costs down seems like it would be much
| more useful for increasing capabilities / proliferating of
| lower end loitering munitions. You can already pack redundant
| navigation systems in more expensive platforms that gets them
| to area of operations. But being able to replace $20,000
| inertial navigation system with $200 board + IR camera makes
| a lot of somewhat cheap smart munitions much smarter, and
| mitigates a lot of expensive electronics warfare platforms.
|
| Starlink ubiquity does seem to open a lot of indirect
| strategic applications, i.e. research using starlink
| transmissions as bi/multistatic illumination source to detect
| stealth flyers.
| phoronixrly wrote:
| Don't get distracted
| https://news.ycombinator.com/item?id=42388354
| alexpotato wrote:
| Fun fact:
|
| The SR-71 and U2 planes had automated celestial navigation
| systems b/c GPS wasn't around when they came out.
|
| There a story in the book about Lockheed Martin's Skunk Works
| where they mention turning on the system while one of the planes
| was in the hangar and it locked on to a hole in the roof (sun was
| shining through the hole and system thought it was a start).
| perihelions wrote:
| And, it's a bit older than that: the SR-71's derived from ICBM
| targeting systems,
|
| https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertia...
| ( _" the latter of which was adapted for the SR-71..."_)
|
| (Actually the very first one, in that history, was an
| intercontinental _cruise missile_ --a jet weapon that slightly
| predated (~1958) rockets powerful enough to cross oceans.
| ICBM's came a bit later. I'm pretty sure the first generation
| were pure-analog circuits, but I forgot where I read about
| that).
| alexpotato wrote:
| Reminds me of the "the distance between the rails of a
| railway are due to the width of Roman horse drawn carts"
| story.
| littlestymaar wrote:
| Isn't that one a hoax though?
| all2 wrote:
| There are a few standards for rail-line widths. I know
| the US is on one standard (I think the narrow width lines
| died out almost 100 years ago at this point). I know that
| Europe has two, or maybe more.
|
| https://en.wikipedia.org/wiki/Standard-gauge_railway <<
| This makes for fun reading if you're interested in that
| sort of thing.
|
| Relevant passage A popular legend that
| has circulated since at least 1937[8] traces the origin
| of the 1,435 mm (4 ft 8+1/2 in) gauge even further back
| than the coalfields of northern England, pointing to the
| evidence of rutted roads marked by chariot wheels dating
| from the Roman Empire.[a][9] Snopes categorised this
| legend as "false", but commented that it "is perhaps more
| fairly labeled as 'Partly true, but for trivial and
| unremarkable reasons.'"[10] The historical tendency to
| place the wheels of horse-drawn vehicles around 5 ft
| (1,524 mm) apart probably derives from the width needed
| to fit a carthorse in between the shafts.[10] Research,
| however, has been undertaken to support the hypothesis
| that "the origin of the standard gauge of the railway
| might result from an interval of wheel ruts of
| prehistoric ancient carriages".[11]
| Neywiny wrote:
| My preferred one for EE folks is that reportedly the first
| Arduino boards (now 20 years old?) had a mistake in their
| eCAD where the second pair of headers was 0.05 instead of
| 0.1" apart. But it was too late by the time they caught it.
| And now, 20 years later, even high end microcontroller
| boards ship with that same gap to be compatible.
| progbits wrote:
| Small correction, one pair is 0.2" apart (so skipping one
| 0.1" pitch space), but the other is 0.16".
| andylynch wrote:
| I understand these still do incorporate celestial navigation.
|
| Since GPS is quite likely going to be unavailable at the time
| of use.
| throw0101c wrote:
| The sensor was sensitive enough that it could detect stars
| during daylight:
|
| * https://theaviationgeekclub.com/the-sr-71-blackbird-astro-
| na...
|
| * https://www.twz.com/17207/sr-71s-r2-d2-could-be-the-key-
| to-w...
|
| * https://en.wikipedia.org/wiki/Missile_guidance#Astro-
| inertia...
| gunian wrote:
| That's insanely cool what kind of cameras / telescope are
| strong enough to do that? My guess is it was primarily
| hardware and not software bacuse of compute limits
|
| Did the planes have to fly above clouds?
| sho_hn wrote:
| Check out the CuriousMarc video series I linked under the
| OP, which gets into the sensor used and the encoding
| scheme.
| joshvm wrote:
| 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 can be done. The device does a scan,
| so it's only accepting a small area on the sky and the
| initial fix can be sped up because you know where/when the
| aircraft is taking off. A lot of tricks to minimize the
| need for "plate solving", like knowing which direction the
| aircraft is pointing within some tolerance.
|
| Info here: https://www.sr-71.org/blackbird/manual/4/4-3.php
|
| It wasn't exactly a simple instrument to use, and it relied
| on a ton of planned course information. You could also do a
| cold midair start after a power outage, but preflight would
| be much more preferable!
|
| Some modern microwave telescopes like BICEP3 have an
| additional optical telescope for star pointing that are
| daylight-usable, but in summer you need to use a big baffle
| tube. The images are taken with a high sensitivity CCD
| camera and you can pick out brighter target stars
| surprisingly well in the images.
| mpetroff wrote:
| 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.
| sho_hn wrote:
| The excellent CuriousMarc YouTube channel just started a new
| video series refurbishing a B-52 astrotracker, going over all
| of this in some detail:
|
| https://www.youtube.com/watch?v=GkEjLqu-JH0&list=PL-_93BVApb...
|
| Recommended.
|
| It also immediately occured to me how much easier this should
| be on a copter, since you don't need a gimbal'd platform :)
| fooblaster wrote:
| why would you think this has stopped? All military aircraft and
| missiles need to operate in gps denied environments and near
| universally have dead reckoning or celestial navigation still.
| UltraSane wrote:
| I read that the US military wants a modernized version of
| celestial navigation to reduce dependence on GPS. With modern
| light amplification technology it might be able to work during
| the day.
| pclmulqdq wrote:
| They have some of these on ships already.
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(page generated 2025-01-20 23:00 UTC)