From: henry@spsystems.net   
      
   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?   
      
   Not literally, no.  The spacecraft *is* arriving at the outer edges of the   
   atmosphere at high speed; the only way to change that is with lots and   
   lots of rocket fuel, totally ridiculously impractical amounts (unless you   
   are talking about advanced nuclear rockets).   
      
   >Has anyone modeled the idea of   
   >unfolding some large wings to add a lot of surface area...   
      
   There has been a little bit of exploration of the idea of very large   
   surface areas.  It doesn't solve all the problems; you do still decelerate   
   relatively rapidly.  But the deceleration happens higher up, in thinner   
   air, and the heating is spread over a larger surface area, so the   
   materials problems are easier.  It's an interesting idea, but there hasn't   
   been funding for full-scale testing, which is what's really required.   
      
   (In fact, there are at least half a dozen unorthodox reentry concepts   
   which *might* work, and look promising, but will become credible to   
   mainstream designers only after a full-scale demonstration.  This is the   
   sort of technology R&D that NASA should be doing, and isn't.)   
      
   The idea of doing a very gradual reentry, spreading the heating out over   
   a long *time*, is appealing in principle, but nobody knows a way to make   
   it work.  There is just no way to *stay up* in thin air that long.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)