From: henry@spsystems.net   
      
   In article <4200a599@duster.adelaide.on.net>,   
   Malcolm Street   wrote:   
   >Potential weight savings from not having to carry oxidiser along means   
   >smaller booster stage and/or larger payload for given booster stage size.   
      
   Note, stage costs are largely insensitive to stage size.  Actual stage   
   costs (as opposed to those claimed by simplistic cost models) are driven   
   strongly by complexity, closeness to leading edge of technology, and   
   thinness of margins, and only very weakly by size.  The big payoff is not   
   reducing the size of a stage -- especially the first stage, which is   
   usually a cheap one -- but eliminating a stage.   
      
   >But will that outweigh the greater weight of the scramjet engine?   
   >No-one knows for sure yet.  The University of Queensland scramjet research   
   >program is quite explicitly looking at using them as the second stage for   
   >launchers as its primary mission.   
      
   Trouble is, using a scramjet as a second stage means you need a first   
   stage and a third stage, presumably both rockets.   
      
   But... you can get into orbit on two rocket stages alone.  In fact, an   
   Atlas III or V or Delta IV can get you to GTO on two rocket stages alone.   
      
   Unless the scramjet weighs nothing and costs nothing, it's quite likely to   
   raise the total cost, not lower it.   
   --   
   "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)