Re: Astra christmas dance and Re: NEOS

From: b_gimle@algonet.se
Date: Thu Dec 23 2004 - 07:16:15 EST

  • Next message: David Brierley: "DMB Obs December 23 a.m."

    The (FIRST) orbit computation of course assumes a circular orbit.
    With such a short observation segment, no non-linearity could be 
    measured, so a proper OD is impossible.
    
    Simple variations but less likely are near apogee of ~28000 km,
    or near perigee of ~50000 km of a very elongated orbit, or
    a slightly wider range of high-eccentricity orbits, if seen while
    ascending or descending (oblique view).
    
    (Actually, re star ID: IS the orientation alt-az, with zenith above the image,
    or mirrored and rotated ??)
    
    ----- Original message -------
    I detected errors in my computations, and some misconceptions in other 
    replies:
    
    I used "tropical" instead of siderial rate of stars, so the value
    0.991(twice) in my .CSV data should be replaced by 0.989
    
    I swapped the declinations of the "fake" observations produced,
    so the corrected obs should be
    2004-12-19 20:50		04:29:03	-7.390
    2004-12-19 20:54		04:32:57	-7.650
    (and FOV becomes 0.510 x 0.383)
    
    New elset produced by FIRST.EXE still needed some RAAN adjustment to
    bring it closer to Astra:
    04-854A                       4.0
    1 94854U 04854A   04354.37075419  .00001200  00000-0  24000-3 0 00002
    2 94854 013.5131 244.6514 0000010 000.0000 000.0000 01.00750200 00000
    
    This mail was (is) sent via webb, and HTML removes duplicate blanks,
    so you must edit the elset before using it.
    
    The fact that it appears to move along an RA great circle in the
    alt/az reference frame does NOT imply that it is in high-i orbit!
    Since the southward motion is just 26% of the eastward motion (in the
    Earth-fixed reference frame) inclination should be near the TLE above.
    
    I have not been able to identify the five or so stars in the 20:48:39
    frame, or the one traversing 20:49:00-20:50:23 (...?) or the brighter
    one 20:53:09, so my positions are from the predicted pos of Astra.
    
    The fact that FindSat lists Astra 3A for BOTH my positions is a
    deficiency of ANY program trying to evaluate a single position in each
    run. To make a match, the time and crosstrack errors should have
    similar value (including sign/direction) for all points used.
    
    I prefer to enter the coordinates into SkyMap's DEEPSKY.TXT file, and
    match the tracks that run parallell to the points, at the right speed.
    
    
    ----- Original Message ----- > UNID;;RA;Dec
    
    > 2004-12-19 20:50;;04:29:02;-7.651;;;1280;;;;;0.512
    > 2004-12-19 20:54;;04:32:58;-7.389;;;960;;;;;0.384
    >
    >04-854A                         3.0
    >1 99854U 04854  A 04354.86927254  .00000000  00000-0  00000-0 0    00
    >2 99854  13.9728 245.0669 0000010   0.0000   0.0000  1.01644026    00
    >
    
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