In the 1960s, the B-52 bomber could navigate by the stars.
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The "Astro Tracker" was the heart of the celestial navigation system. The 4-inch clear bubble stuck out from the top of the aircraft to view the stars. Inside, a telescope and photomultiplier tube tracked a star, steered by motors and prisms.
@kenshirriff Wait is this the inspiration for the R2 units plonked in the back of the Tie Fighters in Star Wars?
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In the 1960s, the B-52 bomber could navigate by the stars. Celestial navigation requires spherical trigonometry, so an analog Angle Computer solved these equations electromechanically. Let's look inside...
@kenshirriff Welcome to the root physics of gyroscopic measures; brought to you by Spin Physics.
Milankovitch would be proud.
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@kenshirriff Welcome to the root physics of gyroscopic measures; brought to you by Spin Physics.
Milankovitch would be proud.
@numodular Although this unit looks like a gyroscope, it is not at all a gyroscope. There is nothing spinning.
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@kenshirriff Do you know what accuracy it could achieve?
I saw an interview with WW2 navigator who said he could only determine the location of the airfield to within 5 miles (with a sextant) .. in a bomber over Germany, he was lucky to even find the right town!
@vk2bea They say that the accuracy was within 0.1 degree.
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@vk2bea They say that the accuracy was within 0.1 degree.
@kenshirriff .. so about 11 km at 34 degrees north.
I guess with a 10 megaton bomb, it's good enough. If Dr Strangelove is anything to go by, the final bombing run used radar
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@numodular Although this unit looks like a gyroscope, it is not at all a gyroscope. There is nothing spinning.
@kenshirriff I shall update the media to stop the spin, and send the astronauts back to the moon
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In the 1960s, the B-52 bomber could navigate by the stars. Celestial navigation requires spherical trigonometry, so an analog Angle Computer solved these equations electromechanically. Let's look inside...
@kenshirriff @siracusa wasn’t there an SR-71 story about it this not working in the southern hemisphere? Or they couldn’t fit both halves in memory or some such?
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In the 1960s, the B-52 bomber could navigate by the stars. Celestial navigation requires spherical trigonometry, so an analog Angle Computer solved these equations electromechanically. Let's look inside...
@kenshirriff is this the same one that was in the SR-71?
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In the 1960s, the B-52 bomber could navigate by the stars. Celestial navigation requires spherical trigonometry, so an analog Angle Computer solved these equations electromechanically. Let's look inside...
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@kenshirriff is this the same one that was in the SR-71?
@dnaunton The SR-71 used a different system, the NAS-14V2 astroinertial navigation system. Nortronics built the SR-71 system and Kollsman built the B-52 system. The B-52 system is said to have also been used in the Hound Dog cruise missile. A very detailed document on the SR-71 star tracker is here: https://audiopub.co.kr/wp-content/uploads/2021/10/NAS-14V2-ANS-System.pdf
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@tanavit @kenshirriff ouchh cet engin.
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@kenshirriff @siracusa wasn’t there an SR-71 story about it this not working in the southern hemisphere? Or they couldn’t fit both halves in memory or some such?
@yertle Yeah, that sounds familiar.
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@nilz not if you wanted to hit a bridge...
@vk2bea @kenshirriff -
For more on the electromechanical Angle Computer, see my article: https://www.righto.com/2026/04/B-52-star-tracker-angle-computer.html
@kenshirriff Thank you, this is a wonderful article! I had been wondering how celestial navigation worked in planes and missiles.
For all practical intents and purposes, this information is useless for me, but reading the article makes me happy.
If knowing how to build a positioning system for a strategic bomber in a post-GPS/GNSS world ever becomes practically useful to me: thank you again and may God help us all.
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@kenshirriff Thank you, this is a wonderful article! I had been wondering how celestial navigation worked in planes and missiles.
For all practical intents and purposes, this information is useless for me, but reading the article makes me happy.
If knowing how to build a positioning system for a strategic bomber in a post-GPS/GNSS world ever becomes practically useful to me: thank you again and may God help us all.
@richrants @kenshirriff I was involved in the development of a star tracker for a satellite: It's basically a camera, a database of all the known stars and some fancy algorithms. You point it at an arbitrary bit of the sky and it gives you you're attitude relative to the rest of the universe, no other external inputs necessary except for the starlight
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@kenshirriff .. so about 11 km at 34 degrees north.
I guess with a 10 megaton bomb, it's good enough. If Dr Strangelove is anything to go by, the final bombing run used radar
I doubted that 10 megaton yield, but indeed, the B-53 had a 9 megaton yield.
It replaced the B-41, a 25 megaton yield device.
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@dnaunton The SR-71 used a different system, the NAS-14V2 astroinertial navigation system. Nortronics built the SR-71 system and Kollsman built the B-52 system. The B-52 system is said to have also been used in the Hound Dog cruise missile. A very detailed document on the SR-71 star tracker is here: https://audiopub.co.kr/wp-content/uploads/2021/10/NAS-14V2-ANS-System.pdf
@kenshirriff @dnaunton this is fascinating. I also congratulate you on one of the clearest summaries of celestial navigation I have read.
Ages ago I read Francis Chichester’s account of his solo float plane flight from New Zealand to Australia in the 1930s, when he pioneered aerial celestial nav. He went into some detail and was undoubtably a kind of genius, but completely incomprehensible! The man was not a writer. Or much of a mechanic… and that almost killed him.
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In the 1960s, the B-52 bomber could navigate by the stars. Celestial navigation requires spherical trigonometry, so an analog Angle Computer solved these equations electromechanically. Let's look inside...
@kenshirriff I was wondering if satellite constellations fucks this up? I think these are still in use and given a dooms day scenario, it's likely anti-SAT weapons will be used and GPS may be jammed or useless.
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In the 1960s, the B-52 bomber could navigate by the stars. Celestial navigation requires spherical trigonometry, so an analog Angle Computer solved these equations electromechanically. Let's look inside...
@kenshirriff i read this as Apple Computer somehow
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In the 1960s, the B-52 bomber could navigate by the stars. Celestial navigation requires spherical trigonometry, so an analog Angle Computer solved these equations electromechanically. Let's look inside...
@kenshirriff That's quite a piece of mechanical engineering. Aircraft machinery is wildly complicated.
The B-58 Hustler had the first digital navigation computer on a plane. They came up with a clever low-resource trig function algorithm called CORDIC. This was later used in the first pocket scientific calculators.
The SR-71 system was informally called R2-D2. That document says it required an air conditioning trailer on the ground.
