Re: Error analysis of ISS / Venus transit paths

From: Thomas Fly (tfly@alumni.caltech.edu)
Date: Mon Jun 21 2004 - 01:08:57 EDT

  • Next message: Ted Molczan: "TJM obs of 2004 Jun 21 UTC and elements"

    Hi Ted,
    
    > So it seems, but I admire your efforts to limit its role to that of the
    weather.
    
    I'm not quite that optimistic!
    
    > While trying to recreate the transit of Jupiter by ISS videotaped by Gary
    Trapuzzano
    
    I finally realized they'd gotten the track from what I posted for Tony Phillips,
    which he mentioned on Science@NASA:
    
    http://science.nasa.gov/headlines/y2004/12may_issjupiter.htm
    I restored the track I'd generated...
    http://iss-transit.sourceforge.net/IssJupiterEncounter-13may04.txt
    
    (At that time, I hadn't fully implemented GTOPO30/SRTM30, so the transit track
    represented 0 elevation.)
    
    I was rather busy around that time, and I must have misread what Gary said- I
    didn't pick up on the (supposed) fact that subsequently, they determined the
    precise location of their observation site.
    
    > since OIG's elsets are derived from observations ...
    
    It seems that the MCC elsets must also be based on observations- that is, the
    starting point must be based upon a measurement of where the ISS is at a
    particular time.  It's my understanding that the "future" MCC TLEs are generated
    by propagating the orbit by numerical integration- at some point, the orbital
    state is then converted to TLE form (i.e., an analytical model).
    
    In any case, it seems you've discovered something interesting and totally
    unexpected.  I'll certainly be interested in investigating this more when I've
    got some time (and had some sleep!), and I imagine some others will as well.
    
    Tom
    
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