Re: BY Classfd Aug 19 (planar search)

From: Bjoern Gimle@GlocalNet (Gimle@GlocalNet)
Date: Thu Aug 20 2009 - 08:19:56 UTC

  • Next message: Brad Young: "Re: NOSS 3 (c) 11731"

    That approach is approximately correct for a geosat.
    In the S, a GEO 4 min early will be about 4.5 min (1.1 deg) E in RA
    
    But an observer moves ~1 deg E in 4 min ( .81 deg of Earth radius at lat 36)
    For a polar satellite at a range of 637 km the orbit displacement in 4 min will be 8.1 
    degrees!
    
    Although a simple formula could be derived for a circular orbit, depending on inclination, 
    azimuth, elevation and height,
    it is not easy for excentric orbits, and the best approach is to make (graphical) 
    predictions with variations on TLE.
    
    Brad, as you see on the charts I sent, the displacement varies a lot with these factors 
    (though height is nearly constant)
    
    /Björn
    
    PS Strictly speaking I interpret "planar search" as meaning the satellite may be anywhere 
    along the orbit, which is very difficult without GOTO programming (or 1-power 
    observation). This was the case with #30588 07005C which was "lost" from 07224 to June 02 
    (09153) when Russell found it.
    The drag uncertainty was several orbits wide!
    
    ----- Original Message ----- 
    From: "Brad Young" ...
    
     Recently I have started trying to guess displacement from that star based on time early 
    or late (eg 1 degree west of star for about 4 minutes early - pretty close since I am at 
    36N latitude.
    
    If this is an approach to a planar search, then I think I get it. If I'm missing 
    something, please let me know.
    
    
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