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The electromechanical angle computer inside the B-52 bomber's star tracker
- kens 6mo agoAuthor here if you have questions about this analog computer...
- sebmellen 6mo agoWas the star tracked manually by the navigator (as in, did they have to manually “look for” and keep track of it)? Fascinating article, but I’m not grokking how it was used in practice.
- kens 6mo agoThe device has a spiral search mechanism to find the star. Then it locked onto the star and automatically tracked it. So this was unlike the Apollo star tracker where the astronaut has to manually aim at the star.
- roger_ 6mo agoThanks, I was looking through the article for exactly that. Does it lock on to a configuration of stars? Really curious how they did this mechanically.
- kens 6mo agoI'll probably write another article on the star tracker itself. But I can give you a quick summary of the spiral search mechanism. It was electromechanical: a motor turned a resolver, a device with coils to generate sine and cosine from the shaft angle. This gives the X and Y deflections for a circle. These signals went through potentiometers that were also turned by the motor to produce constantly growing magnitudes, so you get a spiral. But you need to slow down the motor as you spiral outwards since you're covering a much larger linear region. So the motor also turns a stepping switch that progressively reduces its speed. Once the system finds a star, a complicated feedback mechanism keeps it locked onto the star. There is a spinning slotted disk in front of the photomultiplier tube. If the star is off center, the output will peak when the slot lines up with the star. Thus there is an error signal with phase that indicates the direction to the star. This signal is demodulated to produce X and Y signals that change the aim to move towards the star.
- palm-tree 6mo agoAm I right in thinking it didn't matter which star it locked onto, and it didn't need to know which star it was? Would it be a problem if it locked onto another celestial body (e.g. Venus)?
- kens 6mo agoNo, it needed to lock onto the right star, the one that matched the coordinates. Otherwise, it would be pointing in a random direction. The navigator would check against three different stars to detect an error. The system could also use planets or even the sun for navigation. A special filter was used with the sun to avoid burning out the photomultiplier tube.
- js2 6mo agoAh, so it could be used in the daytime. I read the whole article assuming it was only useful at night. (When else would you be flying a bomber and need high accuracy?)
- teamonkey 6mo agoThe SR-71’s star tracker was so sensitive it could track stars during the day. https://theaviationgeekclub.com/the-sr-71-blackbird-astro-nav-system-aka-r2-d2-worked-by-tracking-the-stars-and-was-so-powerful-that-it-could-see-the-stars-even-in-daylight/ https://theaviationgeekclub.com/the-sr-71-blackbird-astro-na...
- spiritplumber 6mo agobeing halfway to space probably helped
- montyanne 6mo agoI would absolutely love to read something about that - thanks for putting in the work and sharing it. I have a buddy working on restoring a set of binoculars that were attached to the Target Bearing Transmitter system for a US sub from the 50s. Last I heard he was able to find someone that actually had parts of the original schematics for it so that he’s able to machine some new pieces. These things are definitely a labor of love.
- srean 6mo agoReads like a labour of love. Thanks for sharing.
- kens 6mo agoWe couldn't find a wiring diagram so I had to trace out every wire.
- themadturk 6mo agoThis may seem like a stupid question...but what about when it was cloudy? Can I assume the BFF was flying above the clouds most (or all) of the time?
- kens 6mo agoYes, haze and clouds were a problem at low altitudes, but most of the time the aircraft was above the clouds. The Aurora Borealis (northern lights) was potentially a problem; the system included an aurora filter.
- msla 6mo agoSince the article doesn't mention: I've read that ICBMs used celestial navigation. Is this similar to what contemporary missiles used? Do we even know at this point?
- tgsovlerkhgsel 6mo agoAs I understand it, the star altitude is measured relative to an artificial horizon. How did it determine "down" in a moving airplane? Was it essentially doing the high-tech equivalent of dangling a rock on a string with some dampening (in a gyroscopic cage to avoid being affected by the airplane's rotation), or something smarter? When I looked into whether astronavigation would be solvable cheaply or somehow trivially using modern hardware, I found this a surprisingly difficult problem even on a static platform - inclinometers that would get you down to 0.01° accuracy (which would still translate to a ~1 km positional error if I'm not mistaken, roughly what a skilled sailor is supposed to be able to do with a sextant) are expensive even today. With a moving, shaking platform that's changing position (i.e. a perfect gyro will point perfectly in the wrong direction after a few minutes of flight) and might be flying turns (which makes "down" point in the wrong direction) that seems hard to solve.
- kens 6mo agoThe B-52 star tracker used a gyroscope to determine vertical. The Astro Tracker was stabilized by a bunch of motors and synchros so it matched the gyroscope. Thus, the Astro Tracker was a stable platform even as the aircraft pitched and rolled. (Footnote 4 in my article shows the vertical gyro attached to the Astro Tracker.)
- labcomputer 6mo ago> Was it essentially doing the high-tech equivalent of dangling a rock on a string with some dampening (in a gyroscopic cage to avoid being affected by the airplane's rotation), or something smarter? Yes, that is essentially how a gyroscopic artificial horizon works. Consider that the local horizon changes relative to an inertial frame (the stars) as you travel across the surface of a sphere, so even if you could build a perfect gyro that remained stationary in the inertial frame you would need to update the local down as you move. The solution is to slightly weight the gyro cage to bias it to the local down. Now, consider that, in a properly-coordinated turn, the passengers (and gyro) will feel that gravity points straight to the floor :) So the time-constant of the damping is important.
- 6mo ago
- t0mas88 6mo ago> The Angle Computer is one piece of the Astro Compass, a system that locked onto a star and produced a highly accurate heading (i.e., compass direction), accurate to a tenth of a degree. I think it provides ground track information not just heading? Which is far more valuable for aircraft navigation, because the main issue is unpredictable wind drift.
- kens 6mo agoNo, it did not provide ground track. You could manually produce a ground track using the line of position technique described in the article.
- TMWNN 6mo agoIt's amazing, the things that can be done without what we would consider modern technology. The 8-bit Guy recently released a video asking "What if everything still ran out vacuum tubes?" <https://www.youtube.com/watch?v=mEpnRM97ACQ https://www.youtube.com/watch?v=mEpnRM97ACQ>. Conclusion: A surprising amount of things we take for granted today would still be possible.
- po1nt 6mo agoEverytime I read articles like that, I envy the engineers that worked in development of such tools. First microprocessors in jet fighters, electromechanical celestial navigation... And here I am fighting gitlab pipelines.
- SlightlyLeftPad 6mo agoI’m with you. The complexity yet simplicity of these mechanical devices is fascinating.
- echelon 6mo agoNothing is stopping us. One life to experience the universe. Save up for a sabbatical. Find new engineering pastures. It's always rose colored looking back. Not everybody got to work on this. Some people were storming the beaches...
- therobots927 6mo agoAnd some people, specifically Vietnamese and Cambodian civilians, were on the receiving end of your fun little brain teaser. And other people, like Henry Kissinger, drew random dots on a map to tell it where to drop the bombs. https://en.wikipedia.org/wiki/Operation_Menu https://en.wikipedia.org/wiki/Operation_Menu
- kingleopold 6mo agoanother real fact: "Between 1964 and 1973, the United States conducted a covert "Secret War" in Laos, dropping over two million tons of ordnance during 580,000+ bombing missions, "
- therobots927 6mo agoI’m about to read King Leopold’s Ghost. Great choice in username. I must say it’s a little disappointing that things like “secret bombing campaigns” getting declassified don’t lead to much public response.
- chiph 6mo ago> The Atro Tracker also has declination limits of +90° and -47° and a lower altitude limit of -6°. The latitude is limited to the range between -2° and +90°; the system automatically switches hemispheres so both the North and South latitudes are usable. Why would the system need to have a much greater range of declination (celestial sphere) than latitude (Earth spheroid)? Because the Astro Tracker and Angle Computer could flip over to the Southern hemisphere (was this automatic or was there a switch?) having that much declination range seems unnecessary. Perhaps to allow for pitch of the aircraft in flight? BTW, being able to operate in both the Northern & Southern hemispheres was an important capability for the B-52. Previous bombers (B-36 mostly) had the range but not the reliability or in-flight refueling for global reach. Sadly, I didn't get the chance to look at the B-52 at the Museum of Flight when I was there. If you ever meet Charles Simonyi, please thank him for his support of the museum.
- kens 6mo agoIf you're flying in low latitudes, nearly half the stars that you want to use are going to have negative declination, so negative declinations are important. As for the hemisphere switching, this happened automatically.
- chiph 6mo agoOnce in the Southern Hemisphere, they'll need to pick a new set of stars. So their declination would still be expressed negatively? Or is it that they considered the need to navigate below the lower fourth of Argentina a distant possibility?
- kens 6mo agoIt's totally normal to be in the northern hemisphere and looking at stars below the celestial equator. For instance, Sirius is the brightest star in the night sky and is in the southern half of the celestial sphere. So if you wanted to navigate with Sirius, the system had to support negative declination. (They define negative declination as in the opposite N/S hemisphere from the aircraft.)
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- black6 6mo ago> Each knob on the Master Control Panel has a different geometrical shape, allowing the user to distinguish the knobs by feel. Auto manufacturers should take a clue here.
- DavidVoid 6mo agoSee also: the distinct shape of the flap and landing gear levers (which are often located next to each other). https://aviation.stackexchange.com/questions/22680/why-is-the-gear-handle-shaped-the-way-it-is https://aviation.stackexchange.com/questions/22680/why-is-th...
- aaronmdjones 6mo ago... and yet on more than one occasion, pilots have taken off and prematurely retracted the flaps when they meant to retract the gear! Humans fascinate me sometimes. https://assets.publishing.service.gov.uk/media/578defbae5274a0da900011c/Airbus_A320-214_G-EZTZ_08-16.pdf https://assets.publishing.service.gov.uk/media/578defbae5274... https://assets.publishing.service.gov.uk/media/578def27ed915d3cfd000161/Airbus_A319-111_G-EZFA_08-16.pdf https://assets.publishing.service.gov.uk/media/578def27ed915... (Two separate incidents in the same year, on the same day, even) EDIT: Updated links to point to incident reports
- pests 6mo agoRead every word. i liked this detail in the footnotes: > The Astro Compass needed to know approximately where in the sky to find the star, in order to point its sensor in the right direction. The direction didn't need to be exact because the Astro Compass performed a spiral search pattern to find the star. This search pattern covered ±4° in bearing and ±2.5° in altitude. In comparison, the Moon is 0.5° wide, so it's a fairly large target area. ↩
- DarenWatson 6mo agoHonestly that footnote really stood out to me too! the spiral search detail makes the whole system feel a lot more alive than I expected like it’s actively hunting for the star rather than just pointing and hoping.
- roeles 6mo agoThis is also used in laser communication systems to find your peer.
- nathanmcrae 6mo agoLaser trackers (used for metrology) can also use spiral search to find retroreflectors. Although I believe newer models generate a flash of infrared and find them via bright spots in the resulting image from a camera. I imagine modern celestial navigation systems evolved similarly (minus the infrared flash, not very useful for stars).
- lb1lf 6mo agoIn a very similar vein, Ars Technica did a very interesting story on the electromechanical targeting computers on WW2 battle ships a few years ago; the instructional videos embedded in the story are gold. https://arstechnica.com/information-technology/2020/05/gears-of-war-when-mechanical-analog-computers-ruled-the-waves/ https://arstechnica.com/information-technology/2020/05/gears...
- kuzivaai 6mo ago[dead]
- 0xfaded 6mo ago> AI statement: I didn't use AI to write this article (details). Meta, but thank you for including this and suggest even putting it at the top of your articles. I'm now off to bother to read something that someone bothered to write :)
- userbinator 6mo agoI don't think it's necessary --- AI slop is instantly recognisable, but this clearly isn't. Let's not turn this into another divisive diversion.
- thecodemonkey 6mo agoFun! I was just reading about the star tracker in "Skunk Works: A Personal Memoir of My Years at Lockheed". Really fascinating when you're thinking about how this all happened in the 50's and 60's.
- agambrahma 6mo agoThis is crazy impressive ... the kind of thing that should inspire one to do more, much more, than whatever "mere plumbing" one happens to be doing at the moment
- The_Blade 6mo agothis is exactly what i needed to read when i am starting a mini project to turn empty Chewy and Amazon boxes into a new cat maze for my bonded pair of shelter fearsome beasts can i do something with a v1 raspberry pi and myriad idle laptops and gadgets. both Opus 4.7 and i have had enough of each other for a Caturday
- pomian 6mo agoTriggered door flaps that activate after a cat eats a treat, opening new section of maze.
- The_Blade 6mo agothanks and i don't know why i got downvoted. there is a corporeal world. plus one of my critters figured out how to quasi open a cabinet she thinks can access food way above. just wait until she develops opposable thumbs
- ForHackernews 6mo agoSimilar but arguably even more insane is the Minuteman ICBM's inertial guidance computer https://www.righto.com/2024/08/minuteman-guidance-computer.html https://www.righto.com/2024/08/minuteman-guidance-computer.h... > The diagram below shows the guidance system of the Minuteman III missile (1970). This guidance system contains over 17,000 electronic and mechanical parts, costing $510,000 (about $4.5 million in current dollars). The heart of the guidance system is the gyro stabilized platform, which uses gyroscopes and accelerometers to measure the missile's orientation and acceleration.
- wat10000 6mo agoEven nuttier is the one from the Peacekeeper. Float a perfect beryllium sphere in fluorocarbon. Use thrusters to keep it oriented. No gimbal lock, because no gimbals. Six million dollars per unit, in 1987. So good that a system with literally perfect accuracy wouldn't improve accuracy, because error from the system was already well below other sources of inaccuracy in the missile. https://en.wikipedia.org/wiki/Advanced_Inertial_Reference_Sphere https://en.wikipedia.org/wiki/Advanced_Inertial_Reference_Sp...
- ghaff 6mo agoI don't know specifically about Minuteman though a different ICBM uses inertial guidance but also does a star sight to calibrate at some point in its trajectory--says the Internet ahem. And, also yes, the modern inertial navigation that goes into all this is pretty amazing. The not so modern iteration of all this did get us to the moon in 1969.
- runjake 6mo agoBefore GPS (and after), B-52s navigated using redundant Inertial Navigation Systems (INS). The angle computers were removed from the H models in the early to mid 1990s and I doubt they added them back.
- 93po 6mo agoSomeone recreating this and allowing access to it sort of in the style of an escape room business would be pretty cool - motion flight sim where you can learn to fly the plane or learn to operate the other parts of engineer/bombing/navigation etc. And maybe not simulating the problematic "let's bomb human targets" but rather just bullseyes in fields.
- Animats 6mo agoThis is from the era of devices where the I/O was entirely electrical but the computation was mechanical. Most of this stuff came from naval gunnery. The naval "fire control tables" started out as mechanical computers where a rather large number of people were inputting different sensor readings via cranks and dials.[1] Gradually, more of the inputs came in directly from the sensors, and more of the outputs went directly to the gun turrets. The final form of this technology was units the size of a footlocker full of gears, cams, and resolvers, with all-electric inputs and outputs. Such things used to show up in surplus stores. I've seen the restored guidance computer for the Nike missile, at the site in Marin County.[2] That's similar, although ground-based. Analog data came in from radars, was processed with mechanical computation, and control signals went out to the missile. [1] https://en.wikipedia.org/wiki/Admiralty_Fire_Control_Table https://en.wikipedia.org/wiki/Admiralty_Fire_Control_Table [2] https://www.nps.gov/goga/nike-missile-site.htm https://www.nps.gov/goga/nike-missile-site.htm
- kens 6mo agoIf you're looking for more, the book "Between Human and Machine: Feedback, Control, and Computing before Cybernetics" is a detailed history of the development of electromechanical fire control computers and feedback systems.
- aequitas 6mo agoThere are some old training videos that show how this worked: https://www.youtube.com/watch?v=gwf5mAlI7Ug https://www.youtube.com/watch?v=gwf5mAlI7Ug Also the Battleship New Jersey YouTube channel has some nice content on this: https://www.youtube.com/watch?v=szxNJydEqOs https://www.youtube.com/watch?v=szxNJydEqOs
- Animats 6mo agoSee [1] for the basic mechanical components. It's a better scan of the same film the Periscope Film archive sells, which is the first one linked above. No sprocket clatter. [1] https://www.youtube.com/watch?v=s1i-dnAH9Y4 https://www.youtube.com/watch?v=s1i-dnAH9Y4
- 6mo ago
- brcmthrowaway 6mo agoCould Claude make this?
- dnnddidiej 6mo agoClaude Shannon? Probably.
- SecurityPill 6mo agoI wonder if we would ever be able to vibe code the design and 3d print it someday
- enjeyw 6mo agoThe story of the navigator in the photo is also worth a read [1]. Very reminiscent of Joseph Heller’s work. 1. https://www.rbogash.com/B-52/Carls_Letter.html https://www.rbogash.com/B-52/Carls_Letter.html
- kylehotchkiss 6mo agoin a way we're still trying to build stuff like this (world models??)
- matheusmoreira 6mo agoThe Air Almanac... Reminds me of the celestial navigation military training videos: https://youtu.be/UV1V9-nnaAs https://youtu.be/UV1V9-nnaAs
- somat 6mo ago"The second approach was to use a digital computer to determine the solution. This solution was rejected because in 1963, a digital computer was expensive, slow, and less reliable." This inflection point between analog and digital computer is a fascinating one. At one point in time a analog computer made sense and some later point in time you would be foolish to specify anything other than a digital computer. But that time between when it could go either way is interesting. There is a good autobiography by the person responsible for introducing the first digital computer to the navy that provides an interesting view into this era. https://ethw.org/First-Hand:No_Damned_Computer_is_Going_to_Tell_Me_What_to_DO_-_The_Story_of_the_Naval_Tactical_Data_System,_NTDS https://ethw.org/First-Hand:No_Damned_Computer_is_Going_to_T... Now I am vaguely searching for a guide on gear train schematic diagrams, I am sure they had them, you don't reason out something this complicated without one. I know hydraulics has it's own flavor of schematic diagram, which are fascinating if all you have seen are electronic circuits. https://www.hidraoil.com/technical-resources/hydraulic-symbols/ https://www.hidraoil.com/technical-resources/hydraulic-symbo...
- lioeters 6mo ago> No Damned Computer is Going to Tell Me What to DO That is the best title for a story about replacing analog and mechanical instruments with digital computers. A similar process is happening now with natural intelligence, replacing or augmenting the human intellect. An interesting resource I just found: The analog computer museum - https://www.analogmuseum.org/english/ https://www.analogmuseum.org/english/ It has a Library section with lots of downloadable articles in German and English.
- tmoertel 6mo agoCheck out those wire harnesses! Serious workmanship there.
- ButlerianJihad 6mo ago[flagged]
- phist_mcgee 6mo agoWorkpersonship doesn't exactly roll off the tongue.
- anjel 6mo agoNot yet...
- sltr 6mo agoMentioned in the footnotes, CuriousMarc has 3 videos on this device. https://youtu.be/aPIZwqq_W_k?si=wAkRagRx-B06TXwY https://youtu.be/aPIZwqq_W_k?si=wAkRagRx-B06TXwY
- ChrisMarshallNY 6mo agoReminds me a bit of this[0]. I have an iOS app[1] that models its operation. Sextants[2] are damn clever devices, and have been around for about three hundred years. Theodolites[3] are even older, but are used for terrestrial measurements. [0] https://en.wikipedia.org/wiki/Antikythera_mechanism https://en.wikipedia.org/wiki/Antikythera_mechanism [1] https://apps.apple.com/app/id989574753 https://apps.apple.com/app/id989574753 [2] https://en.wikipedia.org/wiki/Sextant https://en.wikipedia.org/wiki/Sextant [3] https://en.wikipedia.org/wiki/Theodolite https://en.wikipedia.org/wiki/Theodolite
- staplung 6mo agoHonest question: how do you track stars during daylight? Is it the case that at the operational altitude of the B-52, bright stars are always visible?
- esaym 6mo agoWhat is wrong with just using a compass??
- kens 6mo agoA compass doesn't work well in polar regions, e.g., if you're flying from the US to the Soviet Union.