From: hrubin@stat.purdue.edu   
      
   In article <11e8hbtfj7d96e0@corp.supernews.com>,   
   Mike Lepore  wrote:   
   >Someone please tell me why spacecraft are designed to reenter the earth's   
   >atmosphere at high speed. Isn't there some way to come down slowly,   
   >so the heat shields wouldn't be needed? Has anyone modeled the idea of   
   >unfolding some large wings to add a lot of surface area, or using   
   >propellers to resist falling, or parachutes? Thank you.   
      
   There is a LOT of energy in an Earth orbit, and altitude makes   
   little difference.  Propellers would be useless until one got   
   into thick enough air, and probably even then; the speed is   
   about 18,000 miles an hour, and propellers are not much use   
   even at 1000.   
      
   I presume shallower angles of entry have been considered, but   
   the air friction gets rather high before wings or parachutes   
   can be used; parachutes have been used for reentry after the   
   speed is low enough.  Until the speed is low enough, just keep   
   the heat outside the critical part of the vehicle, unless you   
   have your antigravity device available.   
      
   >Mike Lepore in New York - email with the 5 deleted   
      
      
      
      
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   This address is for information only.  I do not claim that these views   
   are those of the Statistics Department or of Purdue University.   
   Herman Rubin, Department of Statistics, Purdue University   
   hrubin@stat.purdue.edu         Phone: (765)494-6054   FAX: (765)494-0558   
      
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