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

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NNelsonMinar about 3 hours ago 38 commentsRead Article on righto.com

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chiph•about 1 hour 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•about 1 hour 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.

chiph•39 minutes 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?

kens•30 minutes ago

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.)

0xfaded•18 minutes 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•15 minutes 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•13 minutes 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.

po1nt•about 2 hours 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.

kens•about 1 hour ago

> First microprocessors in jet fighters

Don't get me started on that...

eh_why_not•10 minutes ago

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

kens•8 minutes ago

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-...

SlightlyLeftPad•about 1 hour ago

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

culi•20 minutes 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

colechristensen•14 minutes 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.

kens•9 minutes 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. :-)

echelon•about 1 hour 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...

therobots927•about 1 hour 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

kingleopold•about 1 hour ago

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, "

echelon•36 minutes ago

> your fun little brain teaser.

I was upvoted before this dig. Now I'm negative.

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.

lb1lf•37 minutes 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...

pests•about 1 hour 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•about 1 hour 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.

t0mas88•about 2 hours 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•about 2 hours 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.

kens•about 3 hours ago

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

sebmellen•about 2 hours 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.

kens•about 2 hours 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.

roger_•about 2 hours ago

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.

srean•about 2 hours ago

Reads like a labour of love. Thanks for sharing.

kens•about 2 hours ago

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

black6•about 1 hour 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.

TMWNN•about 2 hours 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.