From: jeff.findley@ugs.nojunk.com   
      
   "Allen Meece"  wrote in message   
   news:20040822223359.28808.00001501@mb-m26.aol.com...   
   > < angle of re-entry that NASA always uses, you might as well be "running   
   > directly into the planet at full speed" instead of "skipping repeatedly   
   > off the top of the atmosphere to shed speed">>   
   >    True. Flying into reentry is more elegant than plunging downward and   
   also   
   > cheaper and easier compared to heavy duty thermal tile systems. It's what   
   we'll   
   > need to do for CATS, cheap access to space.   
      
   It may appear to be more elegant, but it's much harder to do.  This is   
   because you either need a great deal of L/D, or you need to burn fuel to get   
   back out of the atmosphere every time you "skip".  Either way, this would   
   only be a net "win" if you could shead heat from your TPS quickly while out   
   of the atmosphere.  This limits your TPS materials greatly (shuttle tiles   
   don't shead heat quickly).  If your TPS can't shead the heat while out of   
   the atmosphere, the "skipping" trajectory will be worse in terms of total   
   heat load than a "traditional" re-entry.   
      
   >    Critics wrongfully claim it'll take lots of braking fuel to get the   
   speed   
   > down but that's boar wash. The ship is nearly empty so short thrusting   
   will be   
   > enough to slow it down enough to start skipping into the outer atmosphere.   
      
   This is what the shuttle and capsules already do.  The re-entry burn is only   
   big enough to make the orbit intersect the atmosphere.  The reason they   
   don't typically skip is due to the L/D and materials issues.   
      
   Jeff   
      
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