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

"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...

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

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.

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. ↩

> 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.

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

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

> 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.

> 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 :)

> 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.

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.

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

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.

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

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

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.

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.

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...

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.

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?

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

https://youtu.be/UV1V9-nnaAs

What is wrong with just using a compass??

Check out those wire harnesses! Serious workmanship there.

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

Could Claude make this?

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

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