RE: Simultaneous Iridium antenna and solar panel flare

From: Matson, Robert (
Date: Mon Oct 08 2001 - 13:45:46 EDT

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    Hi Ray and List,
    Last week Ray reported:
    "A first for me:  Iridium 45 with a right antenna flare peaking at 20:23:45
    > EDT that was still visible as a solar panel flare began and then peaked at
    > 20:24:11.  What was interesting was the slow rise and fall of the antenna
    > flare, 
    > contrasted with the rather steep/fast rise and fall of the solar panel
    > flare.
    > Thanks to Robert Matson and his Iridflare for making making this a 
    > predictable event."
    You're welcome, Ray!  I was wondering if you had the rise/fall
    durations reversed for the MMA flare vs. the solar array
    flare?  I've seen quite a few of the latter now, and they
    tend to be quite gradual -- often lasting 30 seconds or more --
    in contrast to the comparatively fast rise/fall of a typical
    MMA flare.  Just last night I observed a right-MMA flare from
    Iridium 47 that peaked at around magnitude +1, followed 8 1/2
    minutes later by a solar-array flare from Iridium 11 that
    reached about magnitude -0.5.  The solar array flare had a
    very broad peak, whereas the MMA flare had a very identifiable
    brightest point. This behavior is what you would expect,
    given that the MMA's are more optically flat than the solar
    However, there are three factors that I can think of that might
    lead to abrupt solar-array flares under the right circumstances:
    1.  While the MMAs remain fixed relative to the spacecraft body
    axes, the solar arrays articulate, doing their best to track
    the sun.  In some cases, this might cause an increase in the
    rate of change of the flare angle (i.e. "mirror angle"), which
    would decrease the flare duration.
    2.  Body eclipsing.  Unlike the MMAs which, when viewed from the
    ground, cannot be eclipsed by other parts of the Iridium
    spacecraft, the line of sight from the ground to the solar
    arrays can be partially blocked by the spacecraft body.
    3.  Shadow entry.  Just as for the MMAs, a solar array flare could
    be abruptly cutoff by satellite shadow entry (in which case it
    would be tagged by IRIDFLAR with "Pnb").
    Best wishes,
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