Re: ISS Orbit Tweak?

From: Gerhard HOLTKAMP (
Date: Thu Sep 14 2006 - 16:41:01 EDT

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    I have received some private mail confirming that the small ISS boost was 
    indeed occuring as a side-effect of vernier RCS control by the Shuttle.
    But as Kevin Fetter has remarked it seems to be much smaller in scale to what 
    we have seen last year. It is still worth to keep an eye on it over the next 
    few days as long as Atlantis is still docked to the ISS. Among other things 
    it also *tweaks* my prediction for an upcoming Saturday sun transit of the 
    ISS/Atlantis near my place which I would find interesting to watch given the 
    new addition to the ISS!
    On a related theme if you check the orbit elements for the ISS and the Shuttle 
    as posted by NASA on
    you find them treated as two seperate spacecraft and not one docked system. 
    Each has its own mass, cross section area (or correspondingly different drag 
    coefficients for the TLEs) leading to seperate trajectories. A spot check I 
    did for this evening showed a difference in position of about 2 km between 
    the two (using the correspinding arcs valid for the moment)! 
    Gerhard HOLTKAMP
    Darmstadt, Germany
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