Discussion
Ken Shirriff's blog
t0mas88: > 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: Author here if you have questions about this analog computer...
srean: Reads like a labour of love. Thanks for sharing.
TMWNN: 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.
po1nt: 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: I’m with you. The complexity yet simplicity of these mechanical devices is fascinating.
echelon: 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...
therobots927: 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
pests: 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. ↩
kingleopold: 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, "
therobots927: 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.
lb1lf: 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...
chiph: > 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: 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.
chiph: 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?
0xfaded: > 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 :)
culi: 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
sebmellen: 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.
kens: 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.
roger_: 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.
kens: 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.
montyanne: 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.
kens: > First microprocessors in jet fightersDon't get me started on that...
eh_why_not: But let's say I got you started. What would you want to say about them?
kens: 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-...
colechristensen: 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.
kens: 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. :-)
palm-tree: 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)?
kens: 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.
js2: 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?)
thecodemonkey: 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.
userbinator: 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.
