From: no-spam@invalid.com   
      
   In article <1123238450.135965.65810@f14g2000cwb.googlegroups.com>,   
    Proponent@gmx.net wrote:   
      
   > The shuttle-derived heavy-lift vehicles under discussion would for the   
   > most part be powered by the SSME.  Why use the expensive SSME on an   
   > expendable vehicle when the cheaper RS-68 is available?   
   >   
   > As a bonus, the RS-68 provides more thrust.  It's true that it's   
   > specific impulse is not quite as high, but the ultimate objective here   
   > is to keep costs down rather than to maximize technical performance.   
      
   The shuttle-derived launchers will not be used very often or for very   
   long, so it's better to minimize development risks and time, not   
   operating costs.  This is why the cargo SDLV will be basically Shuttle C   
   (SRBs and ET unchanged, cargo pallet = orbiter with no wings or crew   
   cabin).   
      
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