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).
(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).
- "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]"
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.
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.
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.
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.
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]
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
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.
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.
BICEP3 actually uses a >20 year old CCD camera with analog video output (BICEP Array uses newer cameras, with more modern sensors). Daytime star pointings are possible by using a low-pass filter to block visible light and take advantage of the sensitivity of CCD / CMOS sensors to the near infrared, where the daytime sky is more transparent, combined with baffling.
I would add it also uses an ancient analog TV for manual sighting in combination with the GUI for semi-auto centroiding. I always thought that was funny to see, but it seems to work well enough. Also, inserting that baffle is somewhat terrifying because it slots into a hole next to the main vacuum window and if you dropped it on the membrane, bad things would happen. Always fun to bump into Polies here :)
It depends what you mean by useful. On its own, all you're doing is taking pictures of the sky and figuring out where the camera was pointing (and its field of view). Where it's useful is calibrating the pointing direction of other systems. It's fun to try the software at home (there is a public web interface), you just need a camera that can take long enough exposures to see stars without too much noise.
One of the more "useful" backyard astronomy tasks that is achievable for a dedicated amateur is variable star observation (eg AAVSO), because many stars don't need huge telescopes to observe and it's very expensive for a big observatory to stare at a single patch of sky for weeks. Nowadays we have instruments like LSST which is basically designed for this sort of surveying, but public data are still useful. And you do need to know exactly where you're pointing, so either you do this manually by pointing at a bunch of target stars, or you can use a guide scope that solves the field for you.
With images taken at night, you can run the images through Astrometry.net, which is a blind astrometric solver and will provide you with RA / Dec for most images, as long as you have at least a dozen or two stars visible. The code compares asterisms formed by multiple stars to index files built from Gaia or other similar data. This is the technique that's used more frequently for microwave telescopes located where there's a normal diurnal cycle, e.g., CLASS. The smaller the field of the view, the higher the precision, but it also works fine with a camera with a zoom lens.
BICEP, however, is located at the South Pole on a moving ice sheet, requiring frequent updates to its pointing model, and has six months of continuous daylight, so daytime star pointing observations are required. This requires a different technique. Instead of looking at asterisms with multiple stars, the optical pointing telescope is pointed at a single star using an initial pointing model, the telescope pointing is adjusted until the star is centered, and the offset is recorded. This measurement process is repeated for the few dozen brightest stars, which acquires the data needed for refining the pointing model.
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
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.
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).