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Astro Navigation

Uses the stars to Navigate
 
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Instead of using GPS use optical sensors and Artificial intelligence to guide a craft using the stars. It has no real advantage unless the GPS is shot down, but still its an idea.
SIVOLC, Jul 12 2004

Long Baked Astro-inertial Nav https://en.wikipedi...l_navigation_system
[bs0u0155, Jan 08 2018]

[link]






       " Captain, the clouds are up and the Nav-system has gone down again "
normzone, Jul 12 2004
  

       the only craft that have the stars reliably in sight - satellites - already use that.
loonquawl, May 28 2009
  

       i find the best navigation to be other people. apart from in france
undecided888, May 28 2009
  

       The link says " [i]ts "blue light" source star tracker, which could see stars during both day and night, would continuously track a variety of stars..." How is it possible to see stars during daylight? I mean yes, in theory, but how?
MaxwellBuchanan, Jan 08 2018
  

       By not looking towards the sun, and by being outside the atmosphere, so there's nothing to scatter the sunlight and make the background of the sky blue.   

       Edit: but the link's talking about a plane, not a satellite. Maybe it only works at high altitudes?
Wrongfellow, Jan 08 2018
  

       Maybe so. The phrase "blue light" also suggests that it's using tight spectral filtering - perhaps to see a wavelength that's not scattered much by the atmosphere, or is not abundant in sunlight.
MaxwellBuchanan, Jan 08 2018
  

       Double-dichroic prismatic optical "notch" filter - we could tell you more, but then we'd have to kill you.   

       Imagine an upside-down S.A.B.S. Mk VII, and yet somehow strangely not.
8th of 7, Jan 08 2018
  

       //How is it possible to see stars during daylight? I mean yes, in theory, but how?//   

       The systems use a few tricks, firstly, they're astro- INERTIAL, so a standard inertial system is used to get a general idea of location. These are set on the ground and are very accurate at the beginning of the flight, over time the error tends to accumulate. The point is, the inertial system gives the information on where in the sky to look. I can't find any detailed descriptions on how it worked, I expect it may have been classified until the people who really knew were a bit dead, but I expect you could create a mask with holes for target stars and holes for definatelynotstars, then you could sort of wiggle it around looking for the biggest difference in light.   

       //The phrase "blue light" also suggests that it's using tight spectral filtering//   

       UV would be ideal. UV tends not to bounce around or be emitted by things that aren't stars. That's about the limit of 60's optics anyway, they certainly weren't making 3nm bandpass filters for notches in the solar spectrum.   

       I think the biggest factor is that it was fitted to the SR- 71, and therefore operated at 80-100,000ft where the sky is less optically complex. Modern equivalents for low flying aircraft exist, but even Northrop-Grumman thought they were pretty natty in 2007, so it's clearly harder at 10,000ft than 100,000ft.
bs0u0155, Jan 08 2018
  

       // they certainly weren't making 3nm bandpass filters for notches in the solar spectrum. //   

       So much you know, sonny boy ...   

       // the sky is less optically complex. //   

       No, it's not about complexity, it's the noise floor.   

       // Modern equivalents for low flying aircraft exist, but even Northrop-Grumman thought they were pretty natty in 2007, so it's clearly harder at 10,000ft than 100,000ft. //   

       The technical term is "A right bugger".   

       Look at it this way:   

       During the day, there is a fairly useful optical reference called "The Sun" (the celestial object, not the brand of laminar anus-cleanser) which is quite useful if you have an automatic digital sextant.   

       At night, celestial navigation is Baked and WKTE.   

       If you're high enough (in altitude, not pharmacologically) then it is possible to see stars during daylight hours.   

       It's when you drop down into the soup of the lower atmosphere that things start to get difficult...
8th of 7, Jan 08 2018
  

       //useful optical reference called "The Sun"//   

       Turns out it's a pretty noisy neighbor. I read a few bits of RADAR stuff and apparently it can be used as a reliable source of broadband microwave emissions. I even found a couple of papers from the 40's where passive reading from the moon were possible. Hell, with a modern AESA RADAR the sun and moon should be easy as pie to see. You could probably get an active return off the moon, if you know your speed, altitude and the moon position then the time of flight would probably be enough to triangulate from a single reference. Or you could use a closer reference, give the folks in the ISS a bit of a scare.
bs0u0155, Jan 08 2018
  
      
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