RE: GRACE Satellites

From: Randy John (rjohn@axarosenberg.com)
Date: Thu Apr 25 2002 - 20:15:55 EDT

  • Next message: Matson, Robert: "RE: GRACE Satellites"

    A nadir pointing mirror can not actually reflect the sun to an observer on the ground (except when the satellite is on the horizon).  As seen from the satelite, the altitude of the sun and it's reflection must be the same.  If the sun is above the horizon
    then the reflection will also be above (and not visible from the ground).
    
    Since the mirror is a little bumpy we might still be seeing the sun.  If it is the sun, then the satellite should be brightest when the azimuth of the sun and the satellite are the same.  Alternatively, you might be seeing the reflection of a nice bright
    cloud system over the horizon.
    
    Does the mirror really point directly to nadir?
    
    	Randy
    
    -----Original Message-----
    From: Pinizzotto,Russell [mailto:ZZOTTO@mail.nwmissouri.edu]
    Sent: Thursday, April 25, 2002 4:39 PM
    To: 'seesat-l@satobs.org'
    Subject: GRACE Satellites
    
    
    Group:
    
    I observed both GRACE-1 and GRACE-2 again last night, this time from the
    front yard of my house, to see if they would be visible to the unaided eye.
    They were in Camelopardalis at 22:29 local, 3:29 UT.  They flared for about
    4 - 5 seconds to about the same mag as Polaris (+2.02) compared to the 5.9
    predicted by Heavens-Above.  They were 21.5 seconds apart, like the night
    before.
    
    The flat bottom nadir panel that was pointed out may be responsible.  It's
    certainly large enough when compared to an Iridium satellite.  Can the
    Iridium flare programs be modified to predict this behavior?
    
    Even though they make another pass tonight, the weather is uncooperative!
    
    Thanks Tony and Randy for the comments.
    
    Best Regards,
    Russ
    
    40.35 N; 94.97 W; 330 m ASL
    
    +-------------------------------------------------------+
    
    
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