RE: Iridium 79 - Rotational behavior

From: Matson, Robert (
Date: Mon Nov 27 2000 - 17:42:34 PST

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    Hi Harro,
    > have somebody an information - based on actual observations -about the
    > rotation of our next decayer IRIDIUM 79  ( 1998 - 051D # 25470 ) ? Is it a
    > tumbling about all three axis ? It would be helpful to know more about
    > for a reliable reentry prediction.
    I don't think anyone knows for sure.  Last year there was
    some degree of regularity to Iridium 79's flashes, suggesting
    a spin rather than a tumble, at least over the course of
    a minute or so.  The rotation period used to be around 8
    seconds -- i.e. pretty fast.  There is probably precession
    as well, though on a longer time scale.  Without knowing
    how the spin axis is related to the orbital plane (e.g.
    the spin-axis orientation at perigee relative to the
    velocity vector), the drag at perigee can't be determined
    very accurately.
    Observation of the reentry does not look likely for the
    northern midlatitudes on this one.  Perhaps off the coast
    of Africa near the equator.  --Rob
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