From: ariek@attglobal3.14159265358979323846.net.retro.com   
      
   In message  - "William Malverson"   
    writes:   
   >   
   >   
      
   [snip]   
      
      
   >    If its Isp is 429s (286*1.5), it needs to be 15.6% ship and 84.4% fuel.   
   >Of course, it's also going to want to come back from orbit, so it'll need   
   >another 100 m/s or so to slow down and drop back into the atmosphere.  How   
   >does the heating problem at 8 km/s compare with the heating problem at 1.5?   
      
   1 km/Sec is about the speed of SR-71. At such speed the heating problem   
   had been solved by building most of the structure from titanium. IIRC   
   the fuel had been pre-heated using the friction heat but I don't know   
   if it was absolutely needed to take the heat off or the special fuel   
   used in SR-71 needed to be preheated.   
      
   2 km/Sec is about the speed of X-15. At such speed the heating problem   
   (mostly of the wings) had been solved by making the structure from   
   Inconel-X and allowing the upper and lower skin to move to allow for   
   unequal thermal expansion as a result of great temperature difference   
   between the lower and upper skin.   
      
   8km/Sec - well, we know what this speed requires: either a disposable   
   heat-shield of a capsule or a Shuttle TPS, disadvantages of which had been   
   extensively discussed by the CAIB report.   
      
   >In hundreds of manned space flights, the TPS has only catastrophically   
   >failed once, so I'm going to assume that upgrading SS1's hull to handle   
   >reentry, while not trivial, would not require anything terribly difficult.   
   >   
      
   I disagree: designs for 1 km/Sec, 2 km/Sec, 8 km/Sec are entirely   
   different from each other. What you could manage with the thin long   
   wings of the SS1 at 1 km/Sec would be impossible at 8 km/Sec.   
      
      
   ******************************************************************************   
   *   Arie Kazachin, Israel, e-mail: ariek@attglobal3.14159265358979323846.net *   
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   NOTE: before replying, leave only letters in my domain-name. Sorry, SPAM trap.   
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