From: henry@spsystems.net   
      
   In article ,   
   Andrew Gray   wrote:   
   >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?   
      
   It's within the rules but adds a lot of complexity, and it's not clear why   
   you would bother.   
      
   The big advantage of flight refueling for rockets is that it lets you   
   dodge some of the constraints which make it hard to build an *orbital*   
   HTHL SSTO, e.g. the requirement that the landing gear carry the full   
   takeoff weight.  (Which is bad because landing gear is typically(*) 3% of   
   max takeoff weight... but even with LOX/LH2, an SSTO's *total* dry mass   
   can be only about 10% of takeoff weight.)   
      
   But such constraints are much less onerous in a modest suborbital vehicle,   
   so the payoff for avoiding them is greatly reduced.  I'd be very surprised   
   if refueling was worth the trouble.   
      
   (* As Gary Hudson has noted, there *are* aircraft whose landing gear is   
   rather less than 3% of their max takeoff weight.  "Typically" often means   
   "unless you're seriously clever". )   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)