From: henry@spsystems.net   
      
   In article <58866faa.0401250836.4e153886@posting.google.com>,   
   Zoltan Szakaly  wrote:   
   >But there is a region between standstill and about mach 6 where air   
   >breathing propulsion is very attractive. Simple calculations show that   
   >you can achieve a factor of 10 savings in fuel consumption if you use   
   >ramjet like engines.   
      
   Unfortunately, that's much more attractive for cruising missions than for   
   accelerating ones, because the price is much heavier engines.  Even at   
   modest altitudes, the oxygen content of air is *four orders of magnitude*   
   less, per unit volume, than that of LOX.  So you inevitably need big heavy   
   machinery to handle air.   
      
   (If you thought liquid hydrogen was a "fluffy" propellant, awkward to   
   handle because of its bulk, atmospheric air is enormously worse.)   
      
   >There have been numerous real hardware experiments and proofs of   
   >concept that show the performance of ramjets, ejector ramjets, strut   
   >jets etc. An example of an air augmented rocket is the russian GNOM   
   >missile...   
      
   Yeah, they're fairly interesting for *cruise* missions.  But that's a   
   very different class of problem.   
      
   >This missile has less than half the mass of a rocket.   
      
   Which is of almost no importance, for launchers.  The added mass of the   
   rocket is almost all LOX.  Liquid oxygen is one of the cheapest substances   
   on Earth.  In particular, it's much cheaper than airbreathing engines.   
      
   >Basically my calculations show that you can save the entire first   
   >stage if you build an air breathing booster.   
      
   That's plausible.  But so what?  You've turned a rocket first stage into   
   a jet first stage.  In the process, you've made it harder to build and   
   more difficult to develop.  For what?  To save *LOX*?  WHY???   
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   MOST launched 30 June; science observations running     |   Henry Spencer   
   since Oct; first surprises seen; papers pending.        | henry@spsystems.net   
      
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