The electromechanical angle computer inside the B-52 bomber's star tracker

https://www.righto.com/2026/04/B-52-star-tracker-angle-computer.html

by NelsonMinar • 3 months ago

431 111 3 months ago

kens16• 3 months ago

Author here if you have questions about this analog computer...

sebmellen• 3 months ago

Was 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.

kens16• 3 months ago

The 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.

srean• 3 months ago

Reads like a labour of love. Thanks for sharing.

kens16• 3 months ago

We couldn't find a wiring diagram so I had to trace out every wire.

themadturk2• 3 months ago

This 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?

kens16• 3 months ago

Yes, 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• 3 months ago

Since 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?

tgsovlerkhgsel2• 3 months ago

As 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.

kens16• 3 months ago

The 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• 3 months 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.

t0mas88• 3 months 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.

kens16• 3 months ago

No, it did not provide ground track. You could manually produce a ground track using the line of position technique described in the article.

TMWNN• 3 months ago

It'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>. Conclusion: A surprising amount of things we take for granted today would still be possible.

po1nt2• 3 months ago

Everytime 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• 3 months ago

I’m with you. The complexity yet simplicity of these mechanical devices is fascinating.

echelon2• 3 months ago

Nothing 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...

therobots9273• 3 months ago

And 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

kens16• 3 months ago

First microprocessors in jet fighters

Don't get me started on that...

eh_why_not3• 3 months ago

But let's say I got you started. What would you want to say about them?

culi• 3 months ago

It's a shame the only way to work on problems like these (and make a decent living) is to make tools of war.

The end game of much of silicon valley seems to be government (read: military) contracts. Probably because its the main branch of government that's thoroughly funded

takipsizad• 3 months ago

its also a branch of government that always need research so government contracts are plentiful

vjvjvjvjghv• 3 months ago

Defense also got silicon valley started. So it goes full circle.

hydrogen7800• 3 months ago

I'm shooting from the depths of my memory, but I recall reading that one of the earliest government needs for computers was for the decennial census. At some point, it was requiring more than the 10 years to process the previous censuses (sp?) results.

colechristensen• 3 months ago

Eh, it's easy to get caught by the romanticism of working on things like this, but I assure you besides like 4 people in charge of the big picture, everybody else is dealing with things which are exactly as mundane as things these days. Like putting it through 1000 heat cycles of -40 to 200 degrees and then vibrating it at 2gs for 200 hours and then measuring the tolerances of each part... or being in charge of three lines in a standards document for 2 years negotiating the details with the DoD.

kens16• 3 months ago

I couldn't find the specification for the Angle Computer, but I've found specifications for other devices and you're exactly right: pages and pages of vibration requirements, fungus resistance, testing procedures, and then maybe if I'm lucky one page with useful information like the pinout. This is very annoying if I'm paying by the page. :-)

beachy• 3 months ago

I think the opposite. Hardware is hard, as they say. Building such complex electromechanical designs to military specs without modern CAD tools must have been the equivalent of writing code in binary, without high level languages or even assembler.

mizzao• 3 months ago

It seems GP was appreciating the beauty and purity of engineering required in solving such problems (as opposed to, perhaps, fighting AI slop today).

po1nt2• 3 months ago

I'll take it any day if I wouldn't need to see docker on windows anymore.

chiph2• 3 months 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.

kens16• 3 months ago

If 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.

chiph2• 3 months ago

Once 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?

themadturk2• 3 months ago

The B-52 is one of my favorite aircraft, and the one at the Museum of Flight is an absolute beast -- I never thought it was small, but it's still bigger than I expected.

black6• 3 months 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• 3 months ago

See 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-th...

aaronmdjones• 3 months 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/578defbae5274...

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• 3 months ago

Read 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• 3 months ago

Honestly 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• 3 months ago

This is also used in laser communication systems to find your peer.

nathanmcrae• 3 months ago

Laser 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• 3 months ago

In 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...

0xfaded• 3 months 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• 3 months ago

I 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• 3 months ago

Fun! 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• 3 months ago

This 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_Blade2• 3 months ago

this 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• 3 months ago

Triggered door flaps that activate after a cat eats a treat, opening new section of maze.

ForHackernews• 3 months ago

Similar but arguably even more insane is the Minuteman ICBM's inertial guidance computer 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• 3 months ago

Even 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_Sp...

ghaff3• 3 months ago

I 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• 3 months ago

Before 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• 3 months ago

Someone 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.

Animats3• 3 months ago

This 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

[2] https://www.nps.gov/goga/nike-missile-site.htm

kens16• 3 months ago

If 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• 3 months ago

There are some old training videos that show how this worked: 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

Animats3• 3 months ago

See [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

ghaff3• 3 months ago

I forget where I saw it (probably YouTube someplace) but the fire control systems (including radar) on the Iowa-class battleships apparently way outperformed their Japanese counterparts. The Japanese has a couple (?) ships with bigger guns/longer range but they couldn't actually take advantage of that longer range to hit big US ships.

bethekind• 3 months ago

Off topic, but this is where I see AI going. A tool that condenses work down from requiring a team and a room to a box. We're decades away from that

ghaff3• 3 months ago

Haven't been there in years but the Nike facility in Marin is well worth a visit if you're there when it's open. The control stations were originally on a higher ridge but they have one of the (basically) containers next to the missile sites now. The idea at the time is that they would explode ordinance (originally conventional, later nuclear) above incoming bombers causing a pressure wave that would make them crash.

Was also a Nike base on Angel Island but there's nothing left there but some old concrete pads.

We actually had one of the Nike bases defending Philadelphia literally next to where I grew up. Don't remember personally--was very young--but there were apparently troop manoeuvres on our property from time to time.

Animats3• 3 months ago

There were fourteen Nike sites in the Bay Area.

We may see large numbers of local defense sites again, against drones and medium-range missiles. Israel and Iraq already have that.

jvanderbot• 3 months ago

One of my favorite internet links is an archive of manuals from this era. Especially the Torpedo Data Computer, another fire solution calculator.

Excellent illustrations!

https://maritime.org/doc/tdc/index.php

pram• 3 months ago

Semi-related but people should look at the Sprint missile if they're interested in this, it goes so ridiculously fast the warhead begins to glow.

https://youtu.be/kvZGaMt7UgQ

brcmthrowaway• 3 months ago

Could Claude make this?

dnnddidiej• 3 months ago

Claude Shannon? Probably.

SecurityPill• 3 months ago

I wonder if we would ever be able to vibe code the design and 3d print it someday

enjeyw• 3 months ago

The 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

kylehotchkiss• 3 months ago

in a way we're still trying to build stuff like this (world models??)

matheusmoreira• 3 months ago

The Air Almanac... Reminds me of the celestial navigation military training videos:

https://youtu.be/UV1V9-nnaAs

somat2• 3 months 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_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-symbo...

lioeters2• 3 months 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/

It has a Library section with lots of downloadable articles in German and English.

qsera5• 3 months ago

A similar process is happening now with natural intelligence

LLMs are not AI.

mohamedkoubaa3• 3 months ago

They're making a comeback now, quantum computers are analog

somat2• 3 months ago

That is why I have doubts about their scalability. There are fundamental physics reasons we were able to scale digital computers and were unable to do the same to analog ones.

tmoertel• 3 months ago

Check out those wire harnesses! Serious workmanship there.

sltr• 3 months ago

Mentioned in the footnotes, CuriousMarc has 3 videos on this device. https://youtu.be/aPIZwqq_W_k?si=wAkRagRx-B06TXwY

ChrisMarshallNY• 3 months ago

Reminds 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

[1] https://apps.apple.com/app/id989574753

[2] https://en.wikipedia.org/wiki/Sextant

[3] https://en.wikipedia.org/wiki/Theodolite

staplung• 3 months ago

Honest 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• 3 months ago

What is wrong with just using a compass??

kens16• 3 months ago

A compass doesn't work well in polar regions, e.g., if you're flying from the US to the Soviet Union.

The electromechanical angle computer inside the B-52 bomber's star tracker

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