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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

#211

Post by someplaceguy »

Tommstein wrote: post #207
someplaceguy wrote: post #180

Earlier quoted context omitted.

> 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…

> How were they doing alignment in a hangar to start with, were these roofless hangars?

I don't think so.

You can read more about alignment in page 7, paragraph 10A-23 and the following pages. It'd usually involve using test equipment and manually inputting the current coordinates (e.g. heading, position, altitude, date/time, ...) into the system, from what I understand.

Regardless, the paragraph I mentioned in my previous comment clearly instructs to enable ASTRO mode after the alignment is completed and the airplane is taxiing in the open. It also mentions that in ASTRO mode, the system can confuse the ceiling lights of the hangar for stars (hence why it needs to be disabled inside the hangar), which means that ASTRO mode does track stars on the ground.

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

#212

Post by dredmorbius »

ethbr1 wrote: post #183
dekhn wrote: post #150

Earlier quoted context omitted.

the "quartz crystals" were likely optical flats and they were connected by wringing-on (like a set of gauge blocks). https://en.wikipedia.org/wiki/Optical_flat#Wringing I'm not sure why you'd use an optical flat in a missle nav system, now I'm curious.

My guess would be for physical calibration of the INS gyroscope rotors? https://navsource.org/archives/08/PolarisHistoryGEX1.htm (see bottom / appendix for examples of Polaris-era INS) Given the CEP they were aiming for, and amount of time they had to fiddle with them, I'd guess they started very carefully with the physical precision of components.

CEP: Circular error of probable or probability.

The radius of a circle within which 50% of rounds will be found.

For the V-2 rocket this was 4.5 km.

For the Minuteman III missile, 240m.

Blast effects decrease with the cube of the radius, so a more accurate weapon means a smaller effective warhead. The "Flying Ginsu" AGM-114 Hellfire missile has a CEP of 5 meters or less, and uses blades rather than explosives to minimise any unintended casualties.

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

#213

Post by nullc »

TheRealPomax wrote: post #119

[it] was so powerful that it could see the stars even in daylight That's a very odd thing to say: when you're at 85,000 feet (as noted, the SR-71's cruising altitude), the concept of a blue "daylight" that blocks the view of space only exists below you, not above you [1]. There is not enough Rayleigh scattering at that height to get in the way of a camera looking for stars to map to a star chart. It's pretty much why…

if you use a SWIR camera stars are pretty visible in the daytime even at ground level. Scattering is related to a fourth power of frequency so by the time you're down to IR the amount of scattered light is pretty low.

(which is also why the sky is blue-- or really UV, if we could see it)

The software for plate solving is pretty good. I've had some fun taking movie screenshots and figuring out if the stars are real, and if they're the right hemisphere. (can't be used for location without the time and orientation of the camera)

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

#214

Post by macintux »

someplaceguy wrote: post #211
Tommstein wrote: post #207

Earlier quoted context omitted.

> 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…

> How were they doing alignment in a hangar to start with, were these roofless hangars? I don't think so. You can read more about alignment in page 7, paragraph 10A-23 and the following pages. It'd usually involve using test equipment and manually inputting the current coordinates (e.g. heading, position, altitude, date/time, ...) into the system, from what I understand. Regardless, the paragraph I mentioned in my pr…

I wonder, however, whether it could track stars from the ground during the day. Might well only have worked at night.

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

#215

Post by Ccecil »

My electronics instructor in the 90s had worked in industry in the 70s/80s at Ball aerospace. One of the jobs he worked on there was building at test fixture for the star navigation systems from IIRC the first space shuttle. He said it involved going through thousands of LEDs (expensive at the time) and bin them based on brightness so they could arrange them based on the intensity of the stars.

Interesting to see similar stuff here :)

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

#216

Post by phire »

jvm___ wrote: post #42
fidotron wrote: post #6

Earlier quoted context omitted.

The F22 had an unintentional problem of being unable to cross the international date line, which was discovered when attempting to fly from Hawaii to Japan. Given that it may very well be better to assume that anything untested doesn't work at all and to live within those restrictions.

The space shuttle was untested in flying over the new year between December and January. It needed a clock reset and they weren't about to test that on orbit.

I assume they would have gotten around to testing it if the space shuttle program ever got anywhere near its planned operational capacity.

But with only 4 operational shuttles, ~20 days maximum ndurance and only 5-10 flights per year, it was simply enough to just avoid scheduling any mission in the latter half of December.

(Though, I notice STS-103 departed for an 8 day mission on December 19th 1999. That was cutting it close)

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

#217

Post by avs733 »

kijiki wrote: post #202
avs733 wrote: post #166

Earlier quoted context omitted.

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/

This is the citation I should have provided and completely forgot to.

The most interesting boring book I’ve ever read.

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

#218

Post by avs733 »

keepamovin wrote: post #204
avs733 wrote: post #166

Earlier quoted context omitted.

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?

As I understood it yes. The ability to disarm the other side at will, and prevent any retaliation against cities, was seen as an more offensive capacity

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

#220

Post by networkchad »

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...

When I was in Boy Scouts we had a camping trip to SAC. A snow storm forced us to relocate inside and the Air Force came up with the museum as our temporary sleeping area. I got to sleep about 20 feet away from that SR-71. I will never forget how cool that was.
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