Re: rate of change for USA193 predictions?

From: Björn Gimle @GlocalNet (@GlocalNet)
Date: Mon Feb 11 2008 - 11:49:52 UTC

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    There is no need to speculate:
    The height decrease is nearly proportional to the drag term .00160759
    (=.5*orbits/day^2). So after a week, the effect on pass time is
    .00160759*7*7 orbits. Multiplying by ~92 min period, this gives 7 min.
    For two weeks this gives 29 min, for 25 days a full orbit.
    This are relative to an orbit with NO drag.
    Because of the variability of atmospheric density, and tracking errors,
    we usually expect 15-20% error in the drag term, reducing the expected error
    to 1.5 min over a week.
    Quicksat prints this estimate on prediction lines, SkyMap shows it when an
    elset is reloaded (if the prediction date is set in advance)
    > Ted's last post with the most recent USA193 TLE noted a decay of ~890
    > m/d.  Can anyone speculate on how much error that introduces into  pass
    > calculations over a week or so?
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