XPost: sci.space.shuttle   
   From: nognog@adelphia.net   
      
    wrote in message   
   news:1122575549.091205.19130@f14g2000cwb.googlegroups.com...   
   >I think I understand why objects heat up when going through the   
   > atmosphere and therefore why re-entry vehicles need heat shielding.  My   
   > question is why we don't need heat shielding when launching.  Aren't we   
   > going through the same atmosphere?   
   >   
   > BigKhat   
      
   Going from mach 1 to mach 25 is much more gradual into a thinning and   
   eventuallly zero atmosphere. Coming back is hitting the rapidly increasing   
   atmosphere at mach 25 trying to slow back down to mach 1 in a hurry. If they   
   had a way to slow down to mach 1 in space, then they could come down slower   
   and cooler.   
   >   
      
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