RE: Angular diameter discrepamcy in Calsky

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Tue Apr 19 2011 - 20:03:29 UTC

  • Next message: Thierry Legault: "re: Links to Sun crossing sat images/movies?"

    Thierry Legault wrote:
    
    > I doubt that with orbital data deduced from amateur observations, the
    > accuracy would be sufficient for a transit!
    
    Provided that the elements are reasonably current and based on a reasonable number of observations, the time and track
    accuracy of hobbyist SGP4 TLEs is not far from those produced by professionals using the same model. The Lacrosses are
    in fairly low drag orbits, and are tracked fairly frequently, so our TLEs should be reliable for transits. 
    
    For a quick example, I ran a nearly two month old Lacrosse 2 TLE against observations made in the final days before it
    was de-orbited, in late March 2011. It was 24 s early, and after compensating for Earth's rotation in the interim, the
    typical cross-track residuals between prediction and observation were around 0.03 deg. In this case, there would not
    have been a need to use such old elements, since several day old elements were available, which were accurate in time to
    well within 1 s, with similar cross-track accuracy.
    
    If the latest available elements seem too old and the planned observation is important, then I recommend contacting one
    of us for assistance, well in advance if possible. If the object is in a visibility window then we may be able to update
    the elements in time to improve prediction reliability. At the very least, we can provide realistic advice regarding
    prediction time uncertainty, to help in planning. About once every five years or so, I receive a request from someone
    requiring reliably high precision predictions for one of the KeyHoles or Lacrosse, and am glad to assist when able.
    
    Ted Molczan
    
    _______________________________________________
    Seesat-l mailing list
    http://mailman.satobs.org/mailman/listinfo/seesat-l
    



    This archive was generated by hypermail 2b29 : Tue Apr 19 2011 - 20:04:32 UTC