Re: geo sats to internal power = time for geo sat flares

From: Ralph McConahy (rwmcconahy4@comcast.net)
Date: Sun Aug 31 2008 - 21:31:05 UTC

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    Paul Bridges wrote:
    
    >> could you explain...why going into the earth's shadow
    >> would make geosats flare?  It seems like they would go 
    >> dark at that time. And why just this time of the year?
    >> Is it antennas causing the flare like with Iridiums?
    
    Geometry is the key --
    
    First, it is the solar panels that are causing the flare (unlike the Iridiums where it is antennas). Solar panels, by their very purpose have to point toward the sun. When the sun reflects off a solar panel of a geosat it will only reflect back in the general direction of earth near your local midnight. In the summer or winter, the sun is above or below the equator, so the reflection from the sun bouncing off the solar panels will not beam exactly toward the earth but past the earth over the north pole or below the south pole. During those months the geosat receives sun 24x7 because the earth's shadow is never cast on the satellite (no eclipse).
    
    But just because the sun-to-satellite reflected "beam" off the solar panel isn't being reflected toward earth doesn't mean you can't see the geosat at night. In fact, with a telescope you can see many geosats on any clear night--year around. That's because the sun is reflecting off parts other than the solar panels. It's only when you get a direct reflection off a large solar panel that you see a flare. Which brings us back to the geometry...
    
    For a couple of weeks on either side of each equinox, the earth's shadow eclipses the sun as seen from the satellite (lasts about 70 minutes). During those times, from your location, just before the satellite goes into shadow it will be at the best angle for you to see a flare. Remember, the solar panel is pointing back at the sun. But the reflection itself, as it travels back in the direction of the earth, spreads out. The sun-satellite-observer angle will be such that you will catch some of the reflection (a "flare") just before the satellite goes into shadow. Obviously, when it is in shadow, you can't see it. When it emerges out of shadow you will again have an opportunity for a flare.
    
      Ralph McConahy
      38.3306N, 75.6970W, -25m (WGS84)
    
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