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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

#181

Post by defrost »

dekhn wrote: post #164
defrost wrote: post #116

Earlier quoted context omitted.

It astounds me that this is still a problem in 2023. I company I coded for surveyed the entire Fiji region in 1997, drafting aircraft at 80m ground clearance in long lines across both sides of the 180 longitude line. Every single bit of commercial US GIS software available at the time was garbage and failed to correctly compute line lengths that straddled the 180 longitude line, areas of rectangles that did the same,…

Your software was written in the Buffyverse?

Fair point - the original core version from the mid 80s(?) was written by TerraSense Inc. of Sunnyvale, California.

In the above I was recollecting a code header from ~ 26 years ago, I'm Australian and got a single letter wrong in a district name of country I don't live in.

You okay with that or are you just here to nitpick?

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

#182

Post by gmiller123456 »

porphyra wrote: post #136
gmiller123456 wrote: post #108

Earlier quoted context omitted.

Modern, and even old, sensors absolutely can see stars during the day. It's really a question of magnification. When you magnify the image, the pixels a star falls on don't change much, but the background gets darker because the background is spread over more pixels. I was talking to a grad student who was having an issue getting descent flat frames (images of a uniform field, used to account for dust and optical tra…

That's a very cool anecdote. What did she end up doing? I guess you'll need something like an integrating sphere? https://en.wikipedia.org/wiki/Integrating_sphere Photography reviews often measure vignetting by putting a piece of tissue paper on the lens lol.

That was the only time I got to talk to her, so not sure how she ended up solving it. She was searching for transiting exoplanets, so looking for a star's dip in brightness of less than 1%. Even a bug temporarily flying in front of the star could throw it off.

Some people do use tissue paper, or a t-shirt over the lens, and that works for making pretty pictures. But she said none of them come close to 1% accuracy.

But now you have me wondering how the big telescopes do it. Things like the JWST or HST, or even large ground based scopes don't really have any of those options.

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

#183

Post by ethbr1 »

dekhn wrote: post #150
13of40 wrote: post #101

I'm going to replay this from memory without googling it, just to keep the late 20th century air of some people swapping unverifiable facts in a pub: There was an old friend of my mother's, now deceased, who was a retired engineer. He claimed to be the guy who invented the 2-part tuna can, and was known for handing out end chunks of titanium castings left over from some business he ran. At any rate, he had a couple o…

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.

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

#184

Post by gibspaulding »

runjake wrote: post #133
gibspaulding wrote: post #129

For anyone interested in the SR-71 (and other Cold War era spy planes), Skunkworks by Joe Rich is a fascinating read with lots of fun details about their development. Also, fun fact - in 2025 we will cross over into a period of history where the SR-71 first flew closer to the Wright Flyer than to the present day. Edit: Ben Rich, not Joe Rich. Thanks runjake!

Small correction: Ben Rich, not Joe Rich.

Haha thank you. I meant to check that before clicking submit.

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

#185

Post by AceyMan »

dmix wrote: post #151
jimt1234 wrote: post #103

Earlier quoted context omitted.

There's an A-12 Blackbird at the San Diego Air & Space Museum in Balboa Park. Not an expert, but my understanding is the A-12 was basically the beta version that eventually lead to the SR-71. https://sandiegoairandspace.org/collection/item/lockheed-a-1...

That looks a bit smaller than I expected, from my uninformed opinion. Maybe it's just the angle of the photos. How did it fly for 10hrs (based on the parent article) at high speeds without a ton of space for fuel?

The SR-71 is smaller than you'd think ([edit] to my eyeballs, at least).

As far as fuel goes (a) in a three-dimensional object, "volume adds up fast," and (b) aerial refueling.

(p.s. My dad was a US Navy pilot in the early 60s when celestial navigation was still core curricula.)

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

#186

Post by ethbr1 »

Synaesthesia wrote: post #177

It was a huge waste of money, the US was always a paranoid state which was extraordinarily secure. This is precisely what Eisenhower warned about, the rise of the MIC which has its own self-sustaining logic.

Technically, we built the SR-71 precisely because we were terrified of the Soviets suddenly being able to strike the continental US.

Status quo before ICBMs being strategic bombers, many of which could be neutralized en route.

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

#187

Post by NamTaf »

spookie wrote: post #142
EdwardDiego wrote: post #105

Earlier quoted context omitted.

What kinda specialised monster engines is that plane running, holy hell.

The fuel doesn't ignite at "low" temperatures, one reason is because the whole airplane leaks fuel until it's at an high enough speed. At that point, maybe because of the surface temperature, or the forces it tackles at Mach 3+, the whole thing becomes airtight. At least, that's what I remember.

Yup, at Mach 3+ the fuselage expands so significantly that gaps need to exist when it’s stationary, otherwise it’d buckle. So the gaps mean it leaks fuel when stationary.

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

#188

Post by defrost »

jacquesm wrote: post #156
dmix wrote: post #153

Earlier quoted context omitted.

That would make sense if Google Maps wasn't 18yrs old, but I don't really have opinions on that sort of thing as I've never worked for a large tech company on a mature product. Maybe there's not much motivation to try that hard after a certain time.

Yes, I think I should have made my point better: if you can't dogfood it and the population affected is small people just don't care, especially if there is zero economic incentive. It sucks that it is like that.

Interestingly they're not far (relative to myself in Australia) from Scripps in San Diego .. the ocean research company famous for dolphin research and not ocean tempreture mapping to acoustically track submarines in the cold war.

Scripps authored some pretty decent open source CLI unix mapping software that you could pipe together to do all manner of things data presentation wise that dates back to the 1980s at least.

That could handle line lengths across the 180 longitude line .. they thought globally and ran sensors from California to Hawaii to the South China Sea (and elsewhere in the world).

Even the original Sydney-based digital mapping start-up Where 2 Technologies that spawned Google Maps (not the 3D Google Earth) could handle those calculations (as I recall, they even pulled some libraries from people I worked with) - I'd have to check but I believe Where 2 shared some DNA with ERMapper (Perth, W.Australia based global resource mapping company).

At some point post aquisition they must have rewritten | simplified assumptions and never availed themselves of US open software paid for by their own tax dollars.

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

#189

Post by jki275 »

jacurtis wrote: post #32

> the flight plan was recorded on a punched tape that told the aircraft where to go, when to turn, and when to turn the sensors on and off. This is equally fascinating to me. Before each flight, someone had to generate a flight plan and punch it onto a physical tape, then load it into the plan. T No mid-flight "re-calculating route" if stuff goes wrong. One of the most interesting and under-appreciated aspects of ear…

You're overstating the problem to an extent.

Pilots in WWII had things like the predecessor to TACAN to navigate with -- my grandfather was a pilot in the Army Air Corps and described navigation with radio beacons regularly.

Aircraft Carriers don't move far in the short time CV based aircraft are up -- they just need to navigate back to where they took off from. That's not as hard as it sounds, even with 1940s technology. You just need to navigate to within radio range, which is a couple hundred miles if you're in the air.

At the same time, they did get lost at times.

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

#190

Post by NamTaf »

EdwardDiego wrote: post #105
dboreham wrote: post #21

Earlier quoted context omitted.

Even more impressive seeing it sweat fuel onto the apron in the afternoon sun for a few hours then engine ignition with Chevy V8 start cart, takeoff followed by low level transonic flyby. Fairford IAT 1989.

What kinda specialised monster engines is that plane running, holy hell.

What’s more, at its highest speeds, the engine transitioned from conventional turbojet to mostly ramjet compression by extending/retracting a nose cone within each engine intake. Doing so moved the bow shockwave of the cone so that it reflected inside the engine intake, which had the effect of slowing the Mach 3 air down to subsonic speeds so it could be used for engine combustion. But even still, energies were so high that almost all the thrust came from afterburning - the engine combustion stages were basically just spinning as air went through them.

The whole plane is an engineering tour-de-force, especially considering it was designed with slide rules

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