From: schillin@spock.usc.edu   
      
   dave.harper@gmail.com (David Harper) writes:   
      
   >Andrew Gray  wrote in message news:<   
   lrncfte2g.eob.andrew.gray@compsoc.dur.ac.uk>...   
   >> Afternoon all.   
      
   >> The current foremost contender for the X-Prize is, of course, Scaled   
   >> Composites - expected to formally announce soon, I believe - which uses   
   >> a staged flight method, with horizontal takeoff and landing.   
      
   >> Other contenders use vertical takeoff and landing single-stage vehicles;   
   >> Mr Carmack's group, for example.   
      
   >> Have any groups studied - I don't recall hearing of any, so I suspect   
   >> no-one ran with it - an in-air refuelling system, or would this be   
   >> barred by the competition rules?   
      
   >What's the real difference between high-alt refueling and   
   >"piggybacking"?  Either way, after refueling or release, you're at the   
   >same starting point: 40k to 50k feet up with a full tank.   
      
   >The refueling aspect adds some complexity.   
      
      
   The refueling aspect adds less complexity than the air launch.  The   
   technical challenges of the latter are usually *vastly* underestimated;   
   simply dropping a quarter-ton bomb from an airplane without having it   
   e.g. get caught in the boundary layer and slam back up into the bomber,   
   is a non-trivial thing.  When the air-launched vehicle represents a   
   much larger fraction of the total weight, and is much less robust than   
   a simple bomb and thus not amenable to the simple "use big pyros to   
   kick the thing away so hard it ain't ever coming back" solution,   
   you're into relatively unexplored territory.   
      
   Mid-air refuelling, well, Mitchell Burnside Clapp used to claim that   
   the United States Air Force alone has done more in-flight refuellings   
   in a single *day*, than there have been successful air launches of   
   manned aircraft in the entire history of aviation.  I'm not sure if   
   that's true, but it's certainly within an order of magnitude of true.   
      
      
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