5 ms·

Fun fact: The SR-71 and U2 planes had automated celestial navigation systems b/c GPS wasn't around when they came out. There a story in the book about Lockhee

Fun fact: The SR-71 and U2 planes had automated celestial navigation systems b/c GPS wasn't around when they came out. There a story in the book about Lockheed Martin's Skunk Works where they mention turning on the system while one of the planes was in the hangar and it locked on to a hole in the roof (sun was shining through the hole and system thought it was a start).

perihelions 2y ago
And, it's a bit older than that: the SR-71's derived from ICBM targeting systems, https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertial_guidance https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertia... ("the latter of which was adapted for the SR-71...") (Actually the very first one, in that history, was an intercontinental cruise missile—a jet weapon that slightly predated (~1958) rockets powerful enough to cross oceans. ICBM's came a bit later. I'm pretty sure the first generation were pure-analog circuits, but I forgot where I read about that).
- alexpotato 2y ago
  Reminds me of the "the distance between the rails of a railway are due to the width of Roman horse drawn carts" story.
  - littlestymaar 2y ago
    Isn't that one a hoax though?
    - all2 2y ago
      There are a few standards for rail-line widths. I know the US is on one standard (I think the narrow width lines died out almost 100 years ago at this point). I know that Europe has two, or maybe more. https://en.wikipedia.org/wiki/Standard-gauge_railway https://en.wikipedia.org/wiki/Standard-gauge_railway << This makes for fun reading if you're interested in that sort of thing. Relevant passage A popular legend that has circulated since at least 1937[8] traces the origin of the 1,435 mm (4 ft 8+1⁄2 in) gauge even further back than the coalfields of northern England, pointing to the evidence of rutted roads marked by chariot wheels dating from the Roman Empire.[a][9] Snopes categorised this legend as "false", but commented that it "is perhaps more fairly labeled as 'Partly true, but for trivial and unremarkable reasons.'"[10] The historical tendency to place the wheels of horse-drawn vehicles around 5 ft (1,524 mm) apart probably derives from the width needed to fit a carthorse in between the shafts.[10] Research, however, has been undertaken to support the hypothesis that "the origin of the standard gauge of the railway might result from an interval of wheel ruts of prehistoric ancient carriages".[11]
      - cdot2 2y ago
        I dislike the incorrect usage of "prehistoric". The Roman-era is not prehistoric.
        umeshunni 2y ago
        in theory, the carts could predate Roman history.
  - Neywiny 2y ago
    My preferred one for EE folks is that reportedly the first Arduino boards (now 20 years old?) had a mistake in their eCAD where the second pair of headers was 0.05 instead of 0.1" apart. But it was too late by the time they caught it. And now, 20 years later, even high end microcontroller boards ship with that same gap to be compatible.
    - progbits 2y ago
      Small correction, one pair is 0.2" apart (so skipping one 0.1" pitch space), but the other is 0.16".
  - sandworm101 2y ago
    Lookup why torpedo's are almost universally 21" in diameter. The short version: because that was how big they were last time. There is no reason beyond 21" being usrd once upon a time and nobody wanting to break from it and have the old torpedos not work in the new boats.
    - magicalhippo 2y ago
      H I Sutton, a naval defense analyst, made a nice video on this topic. [1]: https://www.youtube.com/watch?v=cuS0yhwSPMc https://www.youtube.com/watch?v=cuS0yhwSPMc
  - persolb 2y ago
    I've actually used this fact in a related way, for wayfinding. Old school Open-CV was able to see tracks well from an onboard monocular camera, but calibration and scale was annoying. Track width is accurate enough that I was able to use it to input a bunch of head-end video to map the tracks. It was mostly just a modified edge detect where the tracks approximately would be. Once finding the tracks, you could automatically calculate the camera's height, lateral location, and angle.
- andylynch 2y ago
  I understand these still do incorporate celestial navigation. Since GPS is quite likely going to be unavailable at the time of use.
- perihelions 2y ago
  - "pretty sure the first generation were pure-analog circuits" This Wikipedia entry isn't what I had in mind, but it describes an interesting analog mechanism, - "For guidance systems based solely on star tracking, some sort of recording mechanism, typically a magnetic tape, was pre-recorded with a signal that represented the angle of the star over the period of a day. At launch, the tape was forwarded to the appropriate time.[2] During the flight, the signal on the tape was used to roughly position a telescope so it would point at the expected position of the star. At the telescope's focus was a photocell and some sort of signal-generator, typically a spinning disk known as a chopper. The chopper causes the image of the star to repeatedly appear and disappear on the photocell, producing a signal that was then smoothed to produce an alternating current output. The phase of that signal was compared to the one on the tape to produce a guidance signal.[2]" https://en.wikipedia.org/wiki/Star_tracker https://en.wikipedia.org/wiki/Star_tracker
throw0101c 2y ago
The sensor was sensitive enough that it could detect stars during daylight: * https://theaviationgeekclub.com/the-sr-71-blackbird-astro-nav-system-aka-r2-d2-worked-by-tracking-the-stars-and-was-so-powerful-that-it-could-see-the-stars-even-in-daylight/ https://theaviationgeekclub.com/the-sr-71-blackbird-astro-na... * https://www.twz.com/17207/sr-71s-r2-d2-could-be-the-key-to-winning-future-fights-in-gps-denied-environments https://www.twz.com/17207/sr-71s-r2-d2-could-be-the-key-to-w... * https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertial_guidance https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertia...
- gunian 2y ago
  That's insanely cool what kind of cameras / telescope are strong enough to do that? My guess is it was primarily hardware and not software bacuse of compute limits Did the planes have to fly above clouds?
  - sho_hn 2y ago
    Check out the CuriousMarc video series I linked under the OP, which gets into the sensor used and the encoding scheme.
    - gunian 2y ago
      it is kind of crazy and just a testament to people's creativity the plane basically flies using an ipdated version of whag the medieval ships used for navigation totally mind blown
  - joshvm 2y ago
    It would work on the ground, I believe the pilots (normally) had to get a fix before takeoff. You do need to see the sky without cloud cover, but spy satellites were less of a concern back then so less risk of being overflown during a daylight setup. The cameras are basically visible telescopes with very narrow fields of view and good baffling. Only a few stars are bright enough that you can sight off them, but it can be done. The device does a scan, so it's only accepting a small area on the sky and the initial fix can be sped up because you know where/when the aircraft is taking off. A lot of tricks to minimize the need for "plate solving", like knowing which direction the aircraft is pointing within some tolerance. Info here: https://www.sr-71.org/blackbird/manual/4/4-3.php https://www.sr-71.org/blackbird/manual/4/4-3.php It wasn't exactly a simple instrument to use, and it relied on a ton of planned course information. You could also do a cold midair start after a power outage, but preflight would be much more preferable! Some modern microwave telescopes like BICEP3 have an additional optical telescope for star pointing that are daylight-usable, but in summer you need to use a big baffle tube. The images are taken with a high sensitivity CCD camera and you can pick out brighter target stars surprisingly well in the images.
sho_hn 2y ago
The excellent CuriousMarc YouTube channel just started a new video series refurbishing a B-52 astrotracker, going over all of this in some detail: https://www.youtube.com/watch?v=GkEjLqu-JH0&list=PL-_93BVApb5_Gufx3xFN9qW__mL4BUsy2 https://www.youtube.com/watch?v=GkEjLqu-JH0&list=PL-_93BVApb... Recommended. It also immediately occured to me how much easier this should be on a copter, since you don't need a gimbal'd platform :)
deleted 2y ago
[deleted]
fooblaster 2y ago
why would you think this has stopped? All military aircraft and missiles need to operate in gps denied environments and near universally have dead reckoning or celestial navigation still.
deleted 2y ago
[deleted]
Sylamore 2y ago
I recently watched this channels videos on B-52 Astro tracking navigation system repairs: https://www.youtube.com/watch?v=nkvN74wuT8w&list=PL-_93BVApb5_Gufx3xFN9qW__mL4BUsy2&index=2 https://www.youtube.com/watch?v=nkvN74wuT8w&list=PL-_93BVApb... He's got a bunch of other vintage electronics stuff that's from the early space program as well, interesting stuff to see the insides of that gear.
nsonha 2y ago
this makes me realize how lame GPS is, a centralized system that will take every thing down with it, should it ever go down

perihelions 2y ago

And, it's a bit older than that: the SR-71's derived from ICBM targeting systems, https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertial_guidance https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertia... ("the latter of which was adapted for the SR-71...") (Actually the very first one, in that history, was an intercontinental cruise missile—a jet weapon that slightly predated (~1958) rockets powerful enough to cross oceans. ICBM's came a bit later. I'm pretty sure the first generation were pure-analog circuits, but I forgot where I read about that).

alexpotato 2y ago
Reminds me of the "the distance between the rails of a railway are due to the width of Roman horse drawn carts" story.
- littlestymaar 2y ago
  Isn't that one a hoax though?
  - all2 2y ago
    There are a few standards for rail-line widths. I know the US is on one standard (I think the narrow width lines died out almost 100 years ago at this point). I know that Europe has two, or maybe more. https://en.wikipedia.org/wiki/Standard-gauge_railway https://en.wikipedia.org/wiki/Standard-gauge_railway << This makes for fun reading if you're interested in that sort of thing. Relevant passage A popular legend that has circulated since at least 1937[8] traces the origin of the 1,435 mm (4 ft 8+1⁄2 in) gauge even further back than the coalfields of northern England, pointing to the evidence of rutted roads marked by chariot wheels dating from the Roman Empire.[a][9] Snopes categorised this legend as "false", but commented that it "is perhaps more fairly labeled as 'Partly true, but for trivial and unremarkable reasons.'"[10] The historical tendency to place the wheels of horse-drawn vehicles around 5 ft (1,524 mm) apart probably derives from the width needed to fit a carthorse in between the shafts.[10] Research, however, has been undertaken to support the hypothesis that "the origin of the standard gauge of the railway might result from an interval of wheel ruts of prehistoric ancient carriages".[11]
    - cdot2 2y ago
      I dislike the incorrect usage of "prehistoric". The Roman-era is not prehistoric.
      - umeshunni 2y ago
        in theory, the carts could predate Roman history.
- Neywiny 2y ago
  My preferred one for EE folks is that reportedly the first Arduino boards (now 20 years old?) had a mistake in their eCAD where the second pair of headers was 0.05 instead of 0.1" apart. But it was too late by the time they caught it. And now, 20 years later, even high end microcontroller boards ship with that same gap to be compatible.
  - progbits 2y ago
    Small correction, one pair is 0.2" apart (so skipping one 0.1" pitch space), but the other is 0.16".
- sandworm101 2y ago
  Lookup why torpedo's are almost universally 21" in diameter. The short version: because that was how big they were last time. There is no reason beyond 21" being usrd once upon a time and nobody wanting to break from it and have the old torpedos not work in the new boats.
  - magicalhippo 2y ago
    H I Sutton, a naval defense analyst, made a nice video on this topic. [1]: https://www.youtube.com/watch?v=cuS0yhwSPMc https://www.youtube.com/watch?v=cuS0yhwSPMc
- persolb 2y ago
  I've actually used this fact in a related way, for wayfinding. Old school Open-CV was able to see tracks well from an onboard monocular camera, but calibration and scale was annoying. Track width is accurate enough that I was able to use it to input a bunch of head-end video to map the tracks. It was mostly just a modified edge detect where the tracks approximately would be. Once finding the tracks, you could automatically calculate the camera's height, lateral location, and angle.
andylynch 2y ago
I understand these still do incorporate celestial navigation. Since GPS is quite likely going to be unavailable at the time of use.
perihelions 2y ago
- "pretty sure the first generation were pure-analog circuits" This Wikipedia entry isn't what I had in mind, but it describes an interesting analog mechanism, - "For guidance systems based solely on star tracking, some sort of recording mechanism, typically a magnetic tape, was pre-recorded with a signal that represented the angle of the star over the period of a day. At launch, the tape was forwarded to the appropriate time.[2] During the flight, the signal on the tape was used to roughly position a telescope so it would point at the expected position of the star. At the telescope's focus was a photocell and some sort of signal-generator, typically a spinning disk known as a chopper. The chopper causes the image of the star to repeatedly appear and disappear on the photocell, producing a signal that was then smoothed to produce an alternating current output. The phase of that signal was compared to the one on the tape to produce a guidance signal.[2]" https://en.wikipedia.org/wiki/Star_tracker https://en.wikipedia.org/wiki/Star_tracker

throw0101c 2y ago

The sensor was sensitive enough that it could detect stars during daylight: * https://theaviationgeekclub.com/the-sr-71-blackbird-astro-nav-system-aka-r2-d2-worked-by-tracking-the-stars-and-was-so-powerful-that-it-could-see-the-stars-even-in-daylight/ https://theaviationgeekclub.com/the-sr-71-blackbird-astro-na... * https://www.twz.com/17207/sr-71s-r2-d2-could-be-the-key-to-winning-future-fights-in-gps-denied-environments https://www.twz.com/17207/sr-71s-r2-d2-could-be-the-key-to-w... * https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertial_guidance https://en.wikipedia.org/wiki/Missile_guidance#Astro-inertia...

gunian 2y ago
That's insanely cool what kind of cameras / telescope are strong enough to do that? My guess is it was primarily hardware and not software bacuse of compute limits Did the planes have to fly above clouds?
- sho_hn 2y ago
  Check out the CuriousMarc video series I linked under the OP, which gets into the sensor used and the encoding scheme.
  - gunian 2y ago
    it is kind of crazy and just a testament to people's creativity the plane basically flies using an ipdated version of whag the medieval ships used for navigation totally mind blown
- joshvm 2y ago
  It would work on the ground, I believe the pilots (normally) had to get a fix before takeoff. You do need to see the sky without cloud cover, but spy satellites were less of a concern back then so less risk of being overflown during a daylight setup. The cameras are basically visible telescopes with very narrow fields of view and good baffling. Only a few stars are bright enough that you can sight off them, but it can be done. The device does a scan, so it's only accepting a small area on the sky and the initial fix can be sped up because you know where/when the aircraft is taking off. A lot of tricks to minimize the need for "plate solving", like knowing which direction the aircraft is pointing within some tolerance. Info here: https://www.sr-71.org/blackbird/manual/4/4-3.php https://www.sr-71.org/blackbird/manual/4/4-3.php It wasn't exactly a simple instrument to use, and it relied on a ton of planned course information. You could also do a cold midair start after a power outage, but preflight would be much more preferable! Some modern microwave telescopes like BICEP3 have an additional optical telescope for star pointing that are daylight-usable, but in summer you need to use a big baffle tube. The images are taken with a high sensitivity CCD camera and you can pick out brighter target stars surprisingly well in the images.

sho_hn 2y ago

The excellent CuriousMarc YouTube channel just started a new video series refurbishing a B-52 astrotracker, going over all of this in some detail: https://www.youtube.com/watch?v=GkEjLqu-JH0&list=PL-_93BVApb5_Gufx3xFN9qW__mL4BUsy2 https://www.youtube.com/watch?v=GkEjLqu-JH0&list=PL-_93BVApb... Recommended. It also immediately occured to me how much easier this should be on a copter, since you don't need a gimbal'd platform :)

deleted 2y ago

[deleted]

fooblaster 2y ago

why would you think this has stopped? All military aircraft and missiles need to operate in gps denied environments and near universally have dead reckoning or celestial navigation still.

deleted 2y ago

[deleted]

Sylamore 2y ago

I recently watched this channels videos on B-52 Astro tracking navigation system repairs: https://www.youtube.com/watch?v=nkvN74wuT8w&list=PL-_93BVApb5_Gufx3xFN9qW__mL4BUsy2&index=2 https://www.youtube.com/watch?v=nkvN74wuT8w&list=PL-_93BVApb... He's got a bunch of other vintage electronics stuff that's from the early space program as well, interesting stuff to see the insides of that gear.

nsonha 2y ago

this makes me realize how lame GPS is, a centralized system that will take every thing down with it, should it ever go down