From: alcore@uurth.com   
      
   On 21 Jun 2004, LRW wrote:   
      
   [snip]   
   >But it's my uneducated understanding that returning space craft, like   
   >all objects entering our atmosphere, super-heat from the friction of   
   >falling through our atmosphere.   
      
   [snip]   
   >Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne   
   >reach the very edge of the atmosphere? Doesn't it also need the   
   >observe the same careful considerations for reentry?   
      
   Airplanes don't superheat.   
      
   Baseballs and Skydivers don't either.   
      
   It's all about air friction.   
      
   If you are moving through the air, you have to push it aside to get   
   through.  The faster and more energetically you do this the more you will   
   heat it (and it will heat you).   
      
   Spacecraft in orbit superheat on return because they are moving VERY fast   
   as they enter the upper atmosphere.   
      
   Spaceship one is using a trajactory that just barely rises above the   
   atmosphere... and has no "ground speed" at all.   
      
   So instead of smashing into the upper atmosphere at 5 or 6 miles per   
   second (22,000 miles per hour) like a space-shuttle, Spaceship One hits   
   the upper atmosphere at around 1,200 miles per hour.  The energy that it's   
   hull must absorb/shed is therefore only about 5% as much.  This is easy to   
   handle with normal aircraft materials.   
      
   The numbers I've just given are really rough.  But they're not completely   
   wrong.   
      
   I hope this helps.   
      
   Gene Pharr   
   New Orleans, LA   
      
   --   
   Alcore Nilth - The Mad Alchemist of Gevbeck   
   alcore@uurth.com   
      
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