XPost: rec.arts.sf.written, sci.space.policy, sci.physics   
   From: jfindley@cinci.nospam.rr.com   
      
   In article , gossg@gossg.org says...   
   >   
   > Jeff Findley  wrote:   
   >   
   > >In article ,   
   > >rgregoryclark@gmSPAMBLOCKail.com says...   
   > >> The reason why it?s so high for the TSTO is that the first stage has to   
   do a   
   > >> boost back maneuver to return to the launch site. But for the SSTO you   
   just   
   > >> let the Earth rotate beneath you until you are over the landing site then   
   > >> land vertically.   
   > >>   
   > >   
   > >Don't forget Falcon 9 first stages also do a reentry burn to reduce the   
   > >velocity before hitting the atmosphere.  On a reusable SSTO version of   
   > >the same, you'll either need to reserve a *hell of a lot* of propellant   
   > >for that burn or you'll really need to beef up the TPS.   
   >   
   > I was told that since the first stage is almost all fuel by weight, by   
   > the time you've been dumped from the payload, you hardly weigh   
   > anything.  So the boostback is very cheap in fuel.   
      
   I'm not talking about the boost back burn, which is only done when they   
   return to a landing pad at Cape Canaveral Air Force Station.  I'm   
   talking about the reentry burn.  This burn is literally done to slow the   
   stage down so that the first stage doesn't burn up on reentry.  So, if   
   the stage is at orbital velocity (which is what an SSTO would be at in   
   orbit), then you'll need a reentry burn that gets the stage to the same   
   velocity currently used for suborbital reentries.  That's *a lot* of   
   delta-V, which translates into *a lot* of propellant.   
      
   Jeff   
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