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

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

#131

Post by defrost »

pests wrote: post #123
seryoiupfurds wrote: post #91

Earlier quoted context omitted.

Wow, even zooming in and out on that island makes Google Maps skip into the middle of the ocean. Edit: and the nearby Rabi Island has a discontinuity at the meridian in map view. Zooming in on it in satellite view sent the map into a crazy refreshing state with flickering grid lines.

These real-life effects by our decisions in technology sometimes half way around the world are very interesting to me. Similar to how some poeple are unlucky enough to live in their communities geographic center that becomes the default location for GPS lookups for that location.

There was US mapping software (not the international scientific survey semi open source stuff, commercial mapping for US public) in the late 1980s and 1990s that actually had positive longitude displays over the US mainland so that their users didn't have to think in negative numbers.

As I noted elsewhere in this thread, large swathes of US software couldn't handle mapping computations that straddled the date line and it's breathtaking that this is still an issue today.

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

#132

Post by gmiller123456 »

photoGrant wrote: post #124
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…

Put a lens cap on! Then shoot.

That is for taking "dark frames". "Flat frames" need light going through the optics so that things like dust and vengetting can be detected.

This link explains them in more detail:

https://www.highpointscientific.com/astronomy-hub/post/astro...

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

#133

Post by runjake »

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.

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

#134

Post by defrost »

doctor_eval wrote: post #128
defrost wrote: post #121

Earlier quoted context omitted.

It's a longitude issue, not a time zone problem. The distance along the zero latitude equator from -179.99 W to +179.99 E should be relatively easy to compute and yet a large proportion of software in the mapping domain screws that up - even software that controls drones and| used by commercial pilots in the US, etc.

Ok so to clarify it’s not the international date line but the latitude? Which makes more sense to me because the international date line is not actually a straight line.

> to clarify it’s not the international date line but the latitude?

Longitude.

The vertical one that goes from negative to positive at 180 Longitude East or West.

Maybe you should get a map out and have a look.

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

#135

Post by ezconnect »

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…

They also need an initial fix before take off and that could be day or night depending on the mission.

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

#136

Post by porphyra »

gmiller123456 wrote: post #108
porphyra wrote: post #39

How does it see the stars? Even modern CMOS image sensors cannot see the stars during the day.

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.

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

#137

Post by ChatGTP »

missedthecue wrote: post #109
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…

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…

I find it highly inspiring.

I love analog tech, simple but generally insanely robust when done right.

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

#138

Post by someplaceguy »

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…

> 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

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...

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

#139

Post by hackermatic »

cushychicken wrote: post #4

You can see one of these up close - both the device, and the airplane! - at the Evergreen Aerospace Museum in McMinnville, OR. They also have on display another Blackbird payload labeled DEF-H. It’s a nondescript white box which you are allowed to look at, but not allowed to know what it does. XD

It's a fantastic museum, because they not only have this, but the Spruce Goose, the largest wooden airplane ever built (and it is massive)! https://www.evergreenmuseum.org/exhibit/the-spruce-goose/

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

#140

Post by ecommerceguy »

TimTheTinker wrote: post #115
pythonguython wrote: post #83

Earlier quoted context omitted.

You can also get close to an SR-71 at the Robins Air Force Base museum in Georgia, and if you touched it probably nobody would notice

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...

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