Intelsat 512 -- a Superbird-like flasher

From: Matson, Robert (ROBERT.D.MATSON@saic.com)
Date: Sun Dec 22 2002 - 14:46:35 EST

  • Next message: Lloyd Wood: "Re: Intelsat 512 -- a Superbird-like flasher"

    Hi Ed and List,
    
    Thanks, Ed, for your detailed report on Intelsat 512.  It's
    flash behavior (with the 1/2-period phase shift like Superbird's)
    is very good news indeed because it adds further support to
    my theory that the satellite bodies -- and not the solar
    wings -- are the source of the flashes we've been seeing.
    
    The behavior is probably more common than we think since all
    it requires is a decent-sized satellite with a couple specular
    sides facing in opposite directions with normals perpendicular
    to the spin axis.  Since solar wings project from many GEO
    sats in directions perpendicular to the satellite body, and
    these solar wings provide the axis of greatest moment of
    inertia, when the satellite is retired (or dies) it will
    eventually start spinning "paddle-wheel" or "propeller"
    fashion.  This results in the satellite sides having surface
    normals that are always very nearly perpendicular to the
    axis of spin.
    
    Slight mass imbalances will result in a spin axis that is
    not exactly parallel to the faces of the satellite body.
    This is what causes a phase shift.  The greater the
    misalignment of the axis, the longer the time delay between
    the two flash peaks.  In the case of Superbird A (#20040),
    the misaligment is quite small -- less than 0.5 degrees --
    so the time separation between the two flash peaks is only
    a minute or two.
    
    With only a few observations, it should be easy to determine
    a fairly accurate spin axis for Intelsat 512 since we now
    know that the cone angle can be assumed to be 90 degrees.
    The only thing that isn't known yet is the precession rate,
    which will require a few months of observation (or some
    backtracking through prior years' observations) to determine.
    At work I have a file on Intelsat 512, so I probably have
    enough data to estimate the precession rate.  Will report
    back when I have a number.
    
    Best,
    Rob
    
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