From: henry@spsystems.net   
      
   In article <20040125182123.24678.00000800@mb-m16.aol.com>,   
   MattWriter  wrote:   
   >It seems intuitive that, if the technology for SSTO is not quite here yet, it   
   >should be possible to do the job by building an RLV which is almost capable of   
   >SSTO by itself and then add strap-on boosters, solid or liquid.   
      
   Yes, it's plausible.  The original Kistler design was an almost-SSTO with   
   a "launch assist platform" that would carry it up to modest altitude, a   
   low-performance recoverable booster.  And the Roton design apparently had   
   provisions for strap-ons, as a hedge against poor engine performance.   
      
   >Yet I've read that, in RLV design studies, this does not work out.  Why?   
      
   As above, sometimes it does.  When it doesn't, the likeliest reason is   
   structural:  an SSTO needs very light structure, and strap-ons impose   
   concentrated loads that are awkward to handle.  Other considerations   
   include controllability -- most strap-on options do not have thrust   
   vectoring, so the core vehicle has to have enough control authority to   
   maintain control despite the rather higher thrust -- and the tricky   
   process of jettisoning strap-ons.   
   --   
   MOST launched 30 June; science observations running     |   Henry Spencer   
   since Oct; first surprises seen; papers pending.        | henry@spsystems.net   
      
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