From: dietz@dls.net   
      
   TomRC wrote:   
      
   > Can someone explain why, given Zubrin's arguments about launch costs   
   > for the commonly conceived solar to microwave power sat, it isn't far   
   > more effective to simply put large mirrors up at GEO to light up solar   
   > power farms on Earth at night?   
   [...]   
    > I assumed that the mirror could either solar sail   
   > up to GEO, or that there'll be enough LEO to GEO traffic to justify an   
   > inexpensive solar powered tug.   
      
   The 'beam' from a mirror inevitably diverges, due to the nonzero   
   size of the Sun.  The sun (at 1 AU) is about .01 radians across,   
   so the footprint of the beam from a mirror at altitude d is about   
   ,01 d.  This is too large for mirrors at GEO to be practical.   
      
   Mirrors in LEO suffer from shadowing by the Earth itself.   
      
   	Paul   
      
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