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.
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.
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...
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.
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
another 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, "
The revelation of secret bombing campaigns was one of the main reveals of The Pentagon Papers by Daniel Ellsberg. This arguably turned American public opinion against the war decisively as it revealed the USA had no cohesive strategy for winning and was repeatedly lying to the American public about the multiple fronts of the war in Southeast Asia for more than twenty years.
I’m sorry. I’m in a bad mood and that was unecessary. That being said, given the current hyper militarized climate in Silicon Valley, I find this detachment of the science / engineering from its use cases to be more than a little distasteful.
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.
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. :-)
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. ↩
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.
> 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.
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.
It'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.)
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.
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
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
thanks 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
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.
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.)
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.
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.
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.
I'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.
I 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.
Am 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)?
No, 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.
Ah, 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?)
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?
> 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.
> 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 :)
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.
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.
> 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.
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.
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.
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
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
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
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.
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.
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.
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
its also a branch of government that always need research so government contracts are plentiful
Defense also got silicon valley started. So it goes full circle.
> First microprocessors in jet fighters
Don't get me started on that...
But let's say I got you started. What would you want to say about them?
The short answer is that it shows what one can get people to believe through relentless self-promotion. For a longer answer on the first microprocessors: https://spectrum.ieee.org/the-surprising-story-of-the-first-...
Would you consider writing a computer history book?
Maybe at some point. The main problem is that writing a book would require me to focus on one topic, which doesn't seem likely.
Easy, just write multiple books simultaneously /s. Cheers.
I’m with you. The complexity yet simplicity of these mechanical devices is fascinating.
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...
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
another 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, "
I’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.
The revelation of secret bombing campaigns was one of the main reveals of The Pentagon Papers by Daniel Ellsberg. This arguably turned American public opinion against the war decisively as it revealed the USA had no cohesive strategy for winning and was repeatedly lying to the American public about the multiple fronts of the war in Southeast Asia for more than twenty years.
> And some people, specifically Vietnamese and Cambodian civilians, were on the receiving end of your fun little brain teaser.
To make it ABUNDANTLY CLEAR, I was referring to celestial navigation.
I guess we have to blame people who weren't alive at the time for wars we didn't participate in?
My wife is Vietnamese, btw.
I’m sorry. I’m in a bad mood and that was unecessary. That being said, given the current hyper militarized climate in Silicon Valley, I find this detachment of the science / engineering from its use cases to be more than a little distasteful.
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.
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. :-)
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. ↩
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.
> 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.
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.
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?
It'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.)
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.
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
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
Triggered door flaps that activate after a cat eats a treat, opening new section of maze.
thanks 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
Author here if you have questions about this analog computer...
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.
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.)
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?
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.
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.
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.
Thanks, 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.
I'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.
I 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.
Am 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)?
No, 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.
Ah, 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?)
The SR-71’s star tracker was so sensitive it could track stars during the day.
https://theaviationgeekclub.com/the-sr-71-blackbird-astro-na...
Reads like a labour of love. Thanks for sharing.
We couldn't find a wiring diagram so I had to trace out every wire.
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?
> 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.
No, it did not provide ground track. You could manually produce a ground track using the line of position technique described in the article.
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
> 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 :)
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.
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.
The Air Almanac... Reminds me of the celestial navigation military training videos:
https://youtu.be/UV1V9-nnaAs
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...
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.
> 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.
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...
... 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
I wonder if we would ever be able to vibe code the design and 3d print it someday
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.
Could Claude make this?
Claude Shannon? Probably.
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.
in a way we're still trying to build stuff like this (world models??)
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.