Non MMA Iridium flares from SW Virginia

From: Matson, Robert (ROBERT.D.MATSON@saic.com)
Date: Mon Apr 23 2001 - 13:28:57 PDT

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    Hi All,
    
    > > An experienced observer reported the following last night (Apr 21 
    > > EDT) observing from deep southwestern Virginia, USA.
    > > 
    > >  At about 8:30 p.m. Eastern time, as I walked up the driveway I saw
    > >  what appeared to be two Iridium flashes of identical brightness 
    > > (-3 mag., I'd guess), as one faded, another came into view, on the
    > same apparent track, and about 5 degrees in the sky behind the
    > first one. Az = 170d; Alt. 20d.
    > > 
    > > Observer location:
    > > Lat 36.750 Long 81.744 elevation 2000ft
    > 
    Paul Sventek correctly identified Iridium 41 and 77 as
    probable culprits.  Iridium 77 was 15 seconds behind
    Iridium 41, on a track less than 2 degrees east of 77.
    The two were separated about 4 degrees total.
    
    > > Iridium 41 and 77 were both deep in the southern sky over southwest 
    > > Virginia at 8:37pm EDT. If Heavens-Above nor Iridflar could find a 
    > > MMA flare, what caused it? Is this an example of a non-MMA flare? Two 
    > > flares at that?
    > 
    Very likely solar array flares from each satellite.  The solar
    beta angle was 58.3 degrees for Iridium 41, and 58.5 degrees
    for Iridium 77.  Whenever the solar beta angle is greater
    than 40 degrees and less than 65 degrees, the azimuth gimbals
    are locked at 40 degrees, and the elevation gimbal continues
    to swing 0-360 degrees, attempting to maximize the solar
    incidence angle.  At these times, solar panel flares are
    possible.
    
    I'm still coding the solar arrays into an advanced version
    of IRIDFLAR -- will probably be at least another week before
    a beta version is ready for testing.
    
    Best,
    Rob
    
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