From: henry@spsystems.net   
      
   In article ,   
   Mike Swift   wrote:   
   >Henry, maybe you can answer a question I have.  I have been told that   
   >the Shuttle's ET would reenter without burning up if steps were not   
   >taken to depressurize it before reentry.  Is this true, and if so is it   
   >because of its very large surface area compared to its weight?   
      
   Just retaining pressure inside would probably not be enough.  However,   
   the large area and light weight do help, as does the insulation, which is   
   partly an ablator and makes a fair heatshield.  If you could somehow   
   stabilize the tank, so it reentered broadside-on (for maximum frontal   
   area) with a slow spin on its axis (so heating would be spread evenly   
   instead of being concentrated on one side), in theory it should survive   
   reentry.  Landing it intact is left as an exercise for the student. :-)   
      
   In addition to depressurizing it, the tank is deliberately tumbled on   
   separation, to help avoid any chance of this.   
   --   
   MOST launched 30 June; science observations running     |   Henry Spencer   
   since Oct; first surprises seen; papers pending.        | henry@spsystems.net   
      
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