Re: Fobos-Grunt: decay estimate

From: Paul Salanitri (
Date: Tue Dec 20 2011 - 14:28:08 UTC

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    I think I've worked out what the drag profile for Phobos Grunt means.
    The ballistic drag curve correlates with a spacecraft moving through 90
    degrees (see image).
    The clipping of the peak drag (when aligned with the trajectory) is where
    the solar panels eclipse the base and therefore reduce drag).
    Absolute maximum is slightly side on with maximum solar panel, but all the
    base incident to the atmosphere.
    Minimum is edge on when the solar panels present only the edge, and the
    spacecraft sides (including hollow parts) is presented to the atmosphere.
    If this is correct, and nothing else changes to alter the spacecraft
    orientation, it should return to the first "maximum" around 26 December.
    Paul Salanitri
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