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The SR-71 Blackbird Astro-Nav System worked by tracking the stars

theaviationgeekclub.com

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Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#201

Post by jimmyk2 »

gmiller123456 wrote: post #144
nickponline wrote: post #90

I did a toy implementation of a star camera: https://nickp.svbtle.com/star-cameras

The article seems to skip the matching part. I see it in the source code though. But it looks like it's just using two stars, how does that work? I know ASTAP and Astromentry.Net use three or four stars and compute the angles and distances between them.

Each star will give a circle on which you could be located. 2 will be the intersection of 2 circles, which is 2 points. If you have some additional assumptions (e.g. Northern hemisphere), it is possible to eliminate one of the points. Otherwise you need a 3rd point to get a full triangulation.

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#202

Post by kijiki »

avs733 wrote: post #166
missedthecue wrote: post #109

Earlier quoted context omitted.

My father worked on the guidance system for the Trident nuclear missile at Singer-Kearfott for many years and this is mostly accurate. There was a lot of geometry involved. They used to test launch the missiles back during the cold war from submarines off of California. The missile would cross the continental US and land in the water off Florida. The Soviets would invariably send "fishing" boats to measure the tests…

As far as I’m aware test shots of both us Air Force and navy icbms off the west coast went to Kwajalein atoll. Some other interesting details… Naval icbms have star tracking for alignment and correction but land based ones do not. The reasoning is that they are all dead reckoning…which requires knowing the initial location. The silo doesn’t move, but the subs do. Their location is tracked with another inertial guidan…

> there was a lot of pushback inside the us military on investing in increasing the accuracy of naval ICBMs.

The book "Inventing Accuracy" covers this in detail. Fascinating historical perspective.

https://mitpress.mit.edu/9780262631471/inventing-accuracy/

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#203

Post by blamazon »

hangonhn wrote: post #78
colechristensen wrote: post #33

Earlier quoted context omitted.

Still used in spacecraft, a vendor: https://www.ball.com/aerospace/capabilities/technologies-com... What’s actually on aircraft tends to be classified.

It's wild that they're also a household name in the form of mason jars.

And for some, the Ball State University. [1]

[1] https://en.wikipedia.org/wiki/Ball_State_University

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#204

Post by keepamovin »

avs733 wrote: post #166
missedthecue wrote: post #109

Earlier quoted context omitted.

My father worked on the guidance system for the Trident nuclear missile at Singer-Kearfott for many years and this is mostly accurate. There was a lot of geometry involved. They used to test launch the missiles back during the cold war from submarines off of California. The missile would cross the continental US and land in the water off Florida. The Soviets would invariably send "fishing" boats to measure the tests…

As far as I’m aware test shots of both us Air Force and navy icbms off the west coast went to Kwajalein atoll. Some other interesting details… Naval icbms have star tracking for alignment and correction but land based ones do not. The reasoning is that they are all dead reckoning…which requires knowing the initial location. The silo doesn’t move, but the subs do. Their location is tracked with another inertial guidan…

So the confrontational is more because of the perceived shift to offensive ("unprovoked") first strike over "defensive" second strike, rather than any perceived loss of a deterrent second strike capability?

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#205

Post by missedthecue »

avs733 wrote: post #166
missedthecue wrote: post #109

Earlier quoted context omitted.

My father worked on the guidance system for the Trident nuclear missile at Singer-Kearfott for many years and this is mostly accurate. There was a lot of geometry involved. They used to test launch the missiles back during the cold war from submarines off of California. The missile would cross the continental US and land in the water off Florida. The Soviets would invariably send "fishing" boats to measure the tests…

As far as I’m aware test shots of both us Air Force and navy icbms off the west coast went to Kwajalein atoll. Some other interesting details… Naval icbms have star tracking for alignment and correction but land based ones do not. The reasoning is that they are all dead reckoning…which requires knowing the initial location. The silo doesn’t move, but the subs do. Their location is tracked with another inertial guidan…

I'm recounting second hand so can't source anything but here is an SLBM test done in 2021 by a sub off of Florida, and it landed in the South Atlantic. So they must have several different ranges, and possibly it's changed over time.

https://missilethreat.csis.org/us-navy-test-fires-trident-ii...

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#206

Post by verandaguy »

jaybo_nomad wrote: post #195

Semi-related tangent: During the early 1990's I developed a star chart and ephemeris for the (momentarily) fashionable Windows Mobile platform called "Pocket Stars" that calculated one's geographical position from three or more sextant observations, mainly as backup for offshore sailors should their GPS system fail. For reasons I still can't fathom, a contractor for the Israeli military purchased many copies, apparen…

I wasn’t around for the 90s edition of windows phone (at least not enough to understand any of the tech) — i guess for lack of a camera and compass +gyro, would the observations be done out of band and just put into a form?

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#207

Post by Tommstein »

someplaceguy wrote: post #180
Tommstein wrote: post #160

Earlier quoted context omitted.

> The Astro-Nav System didn't work only at cruising altitude, it tracked stars even when the SR-71 was on the ground. [1] > > [1] https://airandspace.si.edu/webimages/collections/full/NAS-14 ... I don't necessarily doubt you, but linking to a 76-page PDF without any indication of where the reader is supposed to find support for your claims is not nearly as convincing as you think it is.

> I don't necessarily doubt you, but linking to a 76-page PDF without any indication of where the reader is supposed to find support for your claims is not nearly as convincing as you think it is. It's funny you say that, because based on almost all the assertions you read here on HN which are taken for granted without any links to support them, you'd think linking to an authoritative PDF would be more convincing tha…

> It's funny you say that, because based on almost all the assertions you read here on HN which are taken for granted without any links to support them, you'd think linking to an authoritative PDF would be more convincing than if I hadn't linked to it. But based on your comment it seems like it works the opposite way (unless I point to the exact place supporting my assertion, presumably).

Not at all, your comment was strictly better for including that link, thanks for including it. It was neat to briefly skim the PDF, even if I don't have time to read the 76 pages of technical documentation.

> I only skimmed the document, so I can't point you to the best place where to look for it. But I can point you to page 31, paragraph 10A-69 which says the following: "When alignment is performed in a hanger, there is a possibility that the system will track false stars (ceiling lights, etc). To prevent this from happening, the INERTIAL ONLY mode is selected and enabled after completion of an alignment. After the airplane taxies into the open, ASTRO INERTIAL mode is selected and enabled". I'm pretty sure this supports my assertion.

Maybe. But that whole paragraph is hard to understand. How were they doing alignment in a hangar to start with, were these roofless hangars?

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#208

Post by cperciva »

jaybo_nomad wrote: post #195

Semi-related tangent: During the early 1990's I developed a star chart and ephemeris for the (momentarily) fashionable Windows Mobile platform called "Pocket Stars" that calculated one's geographical position from three or more sextant observations, mainly as backup for offshore sailors should their GPS system fail. For reasons I still can't fathom, a contractor for the Israeli military purchased many copies, apparen…

For reasons I still can't fathom, a contractor for the Israeli military purchased many copies, apparently so their tanks and troops could remain oriented after all other electronic systems failed.

Possibly in case of EMP attack?

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#209

Post by titzer »

PNewling wrote: post #193
jacquesm wrote: post #143

Earlier quoted context omitted.

It's not just analog tech: it's actual engineering. The hardware we have is amazing, most of our software royally sucks. But software done right is also most impressive.

To be fair, you can do a lot when you throw a near endless supply of money at things. Definitely impressive though.

To get great software, you need a small team and give them extremely clear requirements of what it should do with an assload of extremely clear testcases.

Re: The SR-71 Blackbird Astro-Nav System worked by tracking the stars

#210

Post by GolfPopper »

ecommerceguy wrote: post #140
TimTheTinker wrote: post #115

Earlier quoted context omitted.

There's also one at the March air field museum (attached to March ARB, née March AFB) in Riverside, California.

Theres one at Strategic Air Command Museum in Nebraska. https://www.sacmuseum.org/what-to-see/aircraft/sr-71a-blackb...

I've visited that one. As a someone who grew up during the Cold War, the idea that we've got these once super-secret military aircraft just sitting where any old tourist can walk up and take picture from a few feet away always generates some cognitive dissonance.
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