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    Re: automatic celestial navigation
    From: Frank Reed
    Date: 2007 Dec 06, 14:55 -0500

    Apologies for drifting off-topic here...
    
    There's another way to do automatic navigation: you let the satellite find
    YOU. Ships at sea are easy to detect. A handful of satellites can track
    every vessel on the face of the Earth assuming they're emitting some radio
    noise (the electrical systems of any modern ship's engine produce enough
    radio noise). Then when you need your position, you call up the satellite
    and ask. And needless to say, you can ask it to tell you where your
    "friends" are, too. There have been reports of such systems in actual use
    for years. There are sets of satellites, supposedly operated by the US NRO,
    that travel together in small groups. It's a bit eery: you can see three
    little "stars" gliding across the sky together in a triangle a few degrees
    across if you know where and when to look (google "NOSS trios").
    
    Speaking of satellites, how about using them for small-craft navigation?
    And, no, not GPS satellites. I'm talking about visual observations of low
    orbit satellites. Satellite positions are as predictable as the Moon's, as
    long as you avoid objects which maneuver frequently, like the International
    Space Station. And if using a computer isn't cheating, then you can get a
    line of position by observing a satellite's position in the sky (I'm
    picturing tracking it with binoculars and looking for close approaches to
    moderately bright stars). If I observe a satellite that's 500 nautical miles
    above me, and if I can get its position relative to some star accurate to a
    tenth of a degree, which should be possible, then I can get a line of
    position accurate to about 1 nautical mile. If I have a rough DR position to
    start with, there shouldn't be any problem with mistaken satellite
    identities.
    
     -FER
    
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