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Ships must practice celestial navigation
- jas39 2y agoA smartphone has all the sensors: tilt, clock, camera. Even compass, though hardly needed. This should be enough to build an app to determine position at sea.
- bhhaskin 2y agoThose likely aren't anywhere near accurate enough. And accuracy matters when being off by a few degrees can mean hundreds of miles.
- _yb2s 2y agoYou’re right, but they can be used together with a sextant to instantly preform calculations that can be time consuming and difficult at sea. I use an app to double check my hand calculations.
- bhhaskin 2y agoAt that point though you are using a sextant and a fancy calculator =P
- kragen 2y agoCellphone clocks are quartz crystals. Ordinary quartz crystals have an accuracy of ±10 ppm. That's ±0.001%. That's plenty accurate unless you've been at sea for a long time. 10 ppm of a month is 26 seconds, during which time the equator rotates 12 km (6 arc minutes, 1.9 milliradians). That's not "a few degrees". Of course if you have a GPS signal you can keep time to within nanoseconds, but I suppose we're assuming GPS is jammed. Cellphone cameras typically have pixel pitch on the order of 250 microradians, but star trackers routinely deliver attitude information accurate to less than a tenth of a pixel, so 25 microradians, which is 5 arc seconds, not "a few degrees". Calibrating a star tracker for a mass-market camera with its nonlinear distortions is a pain in the ass but can be done. 25 microradians is 160 meters. SatState from F-Droid shows that my cellphone's accelerometer (tilt sensor) seems to vary by ±0.01m/s² in each of its ≈200ms samples, which is about a milliradian of error, 40× worse than the camera error, about two weeks of clock drift. This isn't "a few degrees" either. Accelerometers can integrate over arbitrarily long periods of time to reduce noise; to reduce noise by 40×, assuming a Gaussian distribution, you need about 1600 samples (320 seconds, 5 minutes and 20 seconds) to average out to the same level as the camera error. (It's easiest if the phone is sitting still during the averaging time, but both the gyros and the star tracker attitude information permit you to usefully average the accelerometer signal over time even when the phone is changing attitude.) You probably do need to calibrate the angle between the accelerometer and the camera, but it probably won't change significantly over time for a given phone. The clock seems like it could be the weak point here, but even the clock is only drifting a few hundred meters a day, and that only produces an east-west error.
- saulpw 2y agoBut what happens when the smartphone is bricked by an EMP, or hacked by a nation-state virus? Haven't you ever seen Battlestar Galactica?
- BenjiWiebe 2y agoCan you actually brick a smartphone with an EMP? They don't have much capture area compared to the grid.
- Ekaros 2y agoAlso at that point I would question can you do anything useful with your ship anyway... Considering just how much electronics and automation modern ships run with.
- nayuki 2y agoThe article opens with: > Any navigation equipment that used electricity was prohibited, including all GPS sources, the Essex’s electronic Voyage Management System (VMS), and the computer-based celestial navigation software STELLA. That defines the scope of the exercise.
- _xerces_ 2y agoCurious how navigation at night was not possible without expensive equipment, sounds like they were relying only on starts in the morning and evening? Are the measuring something like angle of those morning/evening stars or their set/rise times with respect to the sun?
- _yb2s 2y agoIt is not true- the authors sound very inexperienced with celestial navigation. There are many ways including the lunar distance method to get a position at night with regular equipment. The math is more complex than a simple noon solar sighting, but it can be done with just a regular cheap plastic sextant and a watch. It’s also no big deal to go 12 hours with no position. If you know your speed and heading you can accurately estimate your position much longer than that. Overall, they also made it sound almost impossibly difficult for a large team of professionals, when solo and otherwise short handed recreational sailors have been reliably sailing around the world with celestial navigation for more than a century- through all possible conditions.
- danielvf 2y agoNote that they were staying roughly 2 miles within the actual track, while having the bulk of the work being done by a combo of officers and newbs that they had just trained. That's high accuracy standards for celestial nav, not even counting that this is most of other people's first time doing this in anger.
- quercusa 2y agoAnd just how expensive is a bubble sextant?
- wrycoder 2y agoI have one I paid $150 for. But bubble sextants are usually only used on aircraft.
- ianburrell 2y agoI discovered that real Tamaya marine sextants are available on eBay for $100-150. They were 30x that new. My understanding is that the sextants are coming from breaker yards in India where the sextants were left on ships and salvaged.
- throw0101a 2y agoTraining for this was discontinued, but brought back in 2016: * https://www.npr.org/2016/02/22/467210492/u-s-navy-brings-back-navigation-by-the-stars-for-officers https://www.npr.org/2016/02/22/467210492/u-s-navy-brings-bac... Now if only the US (and others) would get their act together and build out a backup system to GNSS. China, for example, has built out an eLoran system: * https://rntfnd.org/2024/10/03/china-completes-national-eloran-network-the-paper/ https://rntfnd.org/2024/10/03/china-completes-national-elora... An old USAF video explaining how the theory works (it assumes a geocentric worldview: the Earth is the centre of the universe (but it's not flat :)): * https://www.youtube.com/watch?v=UV1V9-nnaAs https://www.youtube.com/watch?v=UV1V9-nnaAs
- dzhiurgis 2y ago> Now if only the US (and others) would get their act together and build out a backup system to GNSS They are moving towards quantum navigation (esp subs)
- throw0101a 2y ago> They are moving towards quantum navigation (esp subs) How does that help the merchant marine that is part of the logistical supply chain? Are container ships going to get this quantum nav boxes too? The US pays airlines a retainer to be a reserve fleet [1]: will they get these boxes as well in case of emergency? What happens to all the civilian infrastructure that need navigation and timing signals? Considering only the "military" ramifications of GNSS disruption is myopic. [1] https://en.wikipedia.org/wiki/Civil_Reserve_Air_Fleet https://en.wikipedia.org/wiki/Civil_Reserve_Air_Fleet
- pbhjpbhj 2y agoThe USA who just threatened to invade a few NATO allies? People working with USA for the next few years seems pretty foolhardy. Surely everyone else in NATO needs to be getting together and building it defense system that exclude USA.
- scottLobster 2y ago
- cafard 2y ago> when celestial navigation is all but impossible without advanced, expensive equipment (i.e., a bubble sextant). Compared to what the Navy usually steers by, how advanced and expensive are bubble sextants?
- knallfrosch 2y agoProbably they use a $500,000 computer that fills a room and could be replaced with a $50 Android smartphone with offline Google Maps.
- HPsquared 2y agoSaid Android smartphone relies on clear airwaves and billions worth of GPS satellites.
- 5555624 2y agoA new Tamaya sextant can run about $3,000 and Chinese-made Astra sextants are about a third of that. (Bubble sextants aren't used at sea.) That's the only "expensive" equipment needed for celestial navigation or at least that was the case when I learned it over 40 years ago.
- arter4 2y ago>As The American Practical Navigator (aka “Bowditch”) states, “No navigator should ever become completely dependent on electronic methods. The navigator who regularly navigates by blindly pushing buttons and reading the coordinates from ‘black boxes’ will not be prepared to use basic principles to improvise solutions in an emergency.” I wonder if this mindset is also applied, for example, to the rest of the military. Does the Army regularly practice land navigation? I know they get at least one landnav class, but it is a perishable skill. If you don't practice, you'll soon forget about it. I guess this could also be useful to civilians. Being able to do stuff without relying too much on electronics.
- nradov 2y agoSome Army units, particularly ground combat units, regularly practice land navigation with map and compass. I don't think they typically spend much time on celestial navigation beyond the basics of finding heading based on constellations. They're not usually carrying sextants.
- i_am_proteus 2y agoThere's no real need for celestial navigation on land, the same way there's no need for celestial navigation in most coastal waters: if you can see lines of bearing to known landmarks/navigation markers, you can obtain a fix.
- lupire 2y agoShips are far more isolated than land crews, and direction-finding is much harder at sea than on land. If you're part of an organization that cares where you are and wants you back, you are pretty easy to find your general location venture off on a land journey and get stuck. A single human might be hard to find under a rock or snow, but an army unit that wants to fund is easy to spot.
- paganel 2y agoThe problem with getting lost as an army unit on land is that you might inadvertently get in your enemy's sights before anyone on your side might have had the chance to find you, and at that moment it is game over for said unit. There have been documented a few of these such cases in the war in Ukraine.
- rickcarlino 2y agoHave there been any computer vision systems that can approximate celestial navigation using common sensors like a camera, An electronic compass, and a tilt sensor? Something like a computer vision based auto sextant. This is an idea I have thought about for a while but I have zero background in this area.
- walrus01 2y agoI'm not aware of any specifically, but one of the instruments that can be used as a data point to further reduce error when navigating in a zero-GPS/zero-radio-signal environment is an INS. The very highest precision ones are quite classified and used on submarines. https://en.wikipedia.org/wiki/Inertial_navigation_system https://en.wikipedia.org/wiki/Inertial_navigation_system
- exe34 2y agohttps://play.google.com/store/apps/details?id=com.embarcadero.CamSextant&hl=en https://play.google.com/store/apps/details?id=com.embarcader... not tried it
- Polizeiposaune 2y agoNot exactly what you're looking for, but spacecraft can use optical star trackers which compare what they see to a catalogue of known stars to determine orientation. See, for instance: https://www.rocketlabusa.com/space-systems/satellite-components/star-trackers/ https://www.rocketlabusa.com/space-systems/satellite-compone... https://en.wikipedia.org/wiki/Star_tracker https://en.wikipedia.org/wiki/Star_tracker
- gmueckl 2y agoThe closest unit I can think of right now was the SR-71's celestial navigation unit. I don't know how it worked internally, but it supposedly navigated the spy planes to targets across the globe before GPS existed.
- nine_k 2y agoA number of ICBMs used / uses a similar approach. In space, stars are always visible well, and terrestrial navigation aids may have been jammed or destroyed when ICBMs are put to use.
- cromulent 2y agoThere is a lot of GPS jamming happening these days, especially in the Baltic around Kaliningrad. Makes a lot of sense.
- deleted 2y ago[deleted]
- nayuki 2y ago> analog navigation techniques became relevant again I'm not sure exactly what methods were used in this navigation exercise, but if they write down numbers with finite precision at any point in the process, then the method has at least some digital component to it. Note that digital means the use of digits, not necessarily any involvement of computers or electronics. For example, if they take a reading on a sextant, write down a number, and manually transfer it to a coordinate on paper, then that is a semi-digital process. If they take a number and then look up some kind of trigonometric table, that is definitely digital and not analog. But if the navigation process entirely consists of analog mechanical linkages and at no point any number is read out, then I would deem it 100% analog. > using the radian rule, steering 1 degree off base course for 12 hours at a speed of 16 knots results in nearly 3.5 nm left or right of track (565 yards per hour) This brings up a laughable feature of the US customary measurement "system", a hodge-podge of units with no coherent logic to it: 1 nautical mile ≈ 2025.371... yards, an awkward number that isn't even whole. This is because 1 nautical mile = 1852 metres exact and 1 yard = 0.9144 metre exact. Converting between these units would be a pain. (Whereas at least 1 mile = 1760 yards exact.) Analogously, let's say you're piloting an airplane at an altitude of 15000 feet and have a horizontal distance of 7 nautical miles to your landing site. What would be the descent angle if you flew down in a straight line? The answer is not immediately obvious because you can't do trigonometry on different units. Whereas if I said you're 4572 m high and 12964 m horizontal distance away, then the angle is arctan(4572/12964) ≈ 19.4°. And even if distances are reported in kilometres, even a child knows that 1 km = 1000 m.
- brookst 2y agoWhat a wonderfully pedantic takedown of the conflation of digital and electronic.
- y33t 2y agoBelieve it or not, some people still use slide rules and books on trig tables for this very purpose. They use them too. No sense in having them if you aren't competent at using them.
- fmajid 2y agoSo does that mean USN ships are issued with a precision mechanical chronometer for longitude, like John Harrison's original marine chronometer that won the Royal Navy's Longitude Prize?
- ls612 2y agoAn electric timekeeping device which is not networked would presumably be good enough for this purpose wouldn’t it? The concern is ewar not so much the ship not having electricity.
- fmajid 2y agoIn this application, I would also be concerned about resilience in the event of an EMP strike. Not sure a battery-powered quartz timepiece would survive such, even if it would survive a failure of the ship's electrical systems (not sure if that would matter, as I doubt the ship's propulsion could survive such).
- HPsquared 2y agoIf it doesn't require external communication, it's very easy to harden against EMP. Just put it in a Faraday cage.
- bodhiandphysics 2y agoyou can just put a quartz watch in a faraday cage. That'll be more accurate than any mechanical timepiece. Mechanical clocks have a nasty habit of breaking.
- cguess 2y agoIt's really funny to watch a bunch of people contradict the US Navy when it comes to navigation at sea. No, a cell phone isn't going to work in the middle of the Pacific and no, the US Navy doesn't use Google maps. Go get on an actual boat sometime and sail out of sight of land, you lose cell signal way before you're even over the horizon.
- wakawaka28 2y agoShips do use GPS and so do phones and other devices. What exactly are you trying to say?
- myself248 2y agoA cellphone's GPS only relies on the network for a quickstart. With no network, it takes longer to get the initial fix, but then works perfectly fine.
- throw0101a 2y ago> A cellphone's GPS only relies on the network for a quickstart. The point is not to rely on GPS/GNSS: * https://gpsjam.org https://gpsjam.org
- Tor3 2y agoNot always true. I have devices with GPS which not only relies on a network for getting ephemeris data for the satellites, but they can't function without it. In other words, they don't even try to get ephemeris data through the GPS signal. So, if there's no network, it doesn't work. One of my devices is even a tablet without a SIM card, it only has wifi.. so if I'm near a cafeteria with wifi I can get a fix, and keep it for a while, but without it it's totally stuck. Forever. In any case, as others have said, in the ocean a cellphone is useless for navigation. At least use a standalone satellite navigator. And learn to use paper maps and a sextant, it's actually a lot of fun.
- doodaddy 2y ago> CIC was to notify Lieutenant Commander Stanton if the Essex deviated more than 10 nautical miles (nm) from the planned track. Pretty impressive! USS Essex would cover 10nm in about half an hour, so not much tolerance for going off-course.
- gertrunde 2y agoSomewhat related - https://oceangloberace.com/ https://oceangloberace.com/ A round-the-world yacht race where modern technology is not permitted. (Where 'Modern' = pretty much anything that wasn't in common use in 1970's/1980's). A fair few of the boats that have taken part had previously run the Whitbread Race in 80's. GPS isn't permitted outside of emergency situations, and neither are mobile phones/computers (which are sealed in a bag by race organizers for the duration of each leg). Celestial navigation is required iirc. Other banned items include: - Carbon Fiber - Digital Music (Only cassette tapes permitted!)