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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

#281

Post by icegreentea2 »

KMag wrote: post #239
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…

I interned at the Charles Stark Draper Laboratory 20+ years ago. One of the guys was telling me at lunch about his work that day. He had to run some simulations to tell the Navy if their Trident guidance system needed to be sent back for re-manufacturing after a forklift operator dropped it. My understanding is that the handling crate had some kind of integral rough handling detector. (I presume calibrated weights on…

It's possible that he was describing the worst case scenario (minimal range shot), where they can't spend a lot of time up there.

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

#282

Post by rjsw »

jki275 wrote: post #189
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 techno…

Royal Navy carriers had homing beacons to help their aircraft find the carrier again. The beacon rotated once a minute, the pilots synchronized their watches to the beacon before taking off, when they heard the signal through their headphones the second hand on their watch would indicate the bearing back to the carrier.

RN strike aircraft also had their own radar which made it easier to find things.

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

#283

Post by bookofjoe »

sonthonax wrote: post #252
jonathankoren wrote: post #237

Earlier quoted context omitted.

EMPs are a fantasy. Absolutely and unreservedly a complete fantasy. ZERO have ever been tested, and there’s literally a better use for a nuclear warhead. Not only is it a a completely hypothetical attack, it would look identical to a normal nuclear ICBM attack, and absolutely would result in a traditional retaliatory attack. Why would anyone trade an EMP for all their cities? Literally doesn’t make sense. No one in t…

> Why would anyone trade an EMP for all their cities? ICMBs were a theoretical threat. Cold War doctrine had a more realistic (and less apocalyptic) WWIII that would be fought by tactical nukes and tanks through Europe.

>I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones."

― Albert Einstein

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

#285

Post by heeen2 »

freyfogle wrote: post #53
_moof wrote: post #35

Earlier quoted context omitted.

The International Date Line and the 180-degree line of longitude have bitten a _lot_ of folks who don't think to test at the boundaries.

We had a great example of this in a recent Geomob London talk: ask Google Maps to route from Wairiki, Fiji (-16.8048, 179.9893) to Welagi, Fiji (-16.7349, -179.9439), two villages on the coastal road of the same island and about 10km apart, but as you can see from the coordinates on opposite sides of the anti-meridian. You get "Sorry, we could not calculate driving directions from "Wairiki, Fiji" to "Welagi, Fiji" ht…

I can't get any routing on that island at all, even within the same settlement

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

#286

Post by adolph »

drt5b7j wrote: post #274
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.

Do you think the "software engineering" people are giving engineering a bad name? "Christian scientists" are Christians who attach themselves to the word science because science has such a powerful reputation. In their case I'm not worried about their trickery because everyone recognizes this. Everyone knows that Christian scientists are not scientists. With software engineering it's not as clear. It's possible to cr…

In case you are wondering about all those “reading rooms” you may see in various cities:

Not to be confused with Christianity and science, Christians in Science, Christians in science and technology, or Scientology.

Christian Science is a set of beliefs and practices which are associated with members of the Church of Christ, Scientist. Adherents are commonly known as Christian Scientists or students of Christian Science, and the church is sometimes informally known as the Christian Science church. It was founded in 19th-century New England by Mary Baker Eddy, . . .

https://en.wikipedia.org/wiki/Christian_Science

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

#287

Post by gmiller123456 »

jimmyk2 wrote: post #201
gmiller123456 wrote: post #144

Earlier quoted context omitted.

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.

What you're describing is a lat/lon position fix, but the link nickponline gave is for a plate solver (finding the RA/Dec of stars in an image, and determining the camera orientation). All other plate solvers I've looked at use three or four stars and measure the angles and distances relative to each other. Since nickponline's code appears to only use two, I'm intrigued as to what the angle is being measured relative to. It kinda looks like it requires the image to be oriented with North as up, which seems like an interesting twist. It seems a little like cheating, but honestly most people will know the orientation of their camera, and it probably speeds up the search considerably, and would reduce/eliminate the need for building index files.

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

#288

Post by adolph »

dboreham wrote: post #21
cmiller1 wrote: post #9

Earlier quoted context omitted.

I got to see an SR-71 on display in New York several years ago. What really struck me was how BIG it was, seeing pictures of it doesn't really give you sense of scale, it was a massive plane.

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.

As I read it, not just one v8 but two, with straight pipes:

https://www.thesr71blackbird.com/Aircraft/Engines/starting-t...

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

#289

Post by KineticLensman »

mnw21cam wrote: post #268
dekhn wrote: post #157

Earlier quoted context omitted.

In my experience, if there was a well-defined problem in the 70s or 80s, some clever person came up with a workable solution using a tiny microprocessor with limited RAM. The way I think about it is... when I was a kid I hated waiting at lights and imagined you could build a computer vision/ML system (this was in the '80s) that coudl recognize traffic and change the light to green when it was safe, rather than timing…

And then someone rolls up with a bicycle, and because it doesn't have as much metal in it as the detector expects, they end up sitting at a red light forever. Been there, done that.

> And then someone rolls up with a bicycle

My local town has a roundabout with a cut-through lane for buses. The cut-through has a traffic light to help the bus emerge. Every so often, a (presumably non-local) car driver accidentally enters the bus lane, and then has to wait for the next bus to trigger the traffic light.

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

#290

Post by KineticLensman »

dredmorbius wrote: post #212
ethbr1 wrote: post #183

Earlier quoted context omitted.

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 mini…

That would be the AGM-114R9X. Most hellfire variants use explosive warheads.
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