XPost: sci.space.shuttle, sci.space.history, rec.aviation.military   
   From: jeff.findley@ugs.nojunk.com   
      
   "dan"  wrote in message   
   news:1141519892.617552.91260@z34g2000cwc.googlegroups.com...   
   > Various attempts have been made to design hypersonic airbreathing   
   > engines. The X-43 is probably the only one to fly, even briefly. The   
   > problem with scramjets is that they tend to be efficient only in a   
   > narrow range of speeds; great for a cruise missile but not for orbital   
   > launch. The liquid air cycle (i.e. hotol) is less speed sensitive but   
   > there's no easy way to carry enough cooling capacity to actually   
   > liquify all the air you need.  Best bet might essentially be a   
   > cooled-inlet turbojet.  Wings can be useful for thrust-limited designs,   
   > but a launch vehicle goes through the speed regiemes quickly and above   
   > about 30 KM wings aren't much use.  After attacking the SSTO problem   
   > for awhile, at some point a two-stage solution begins to look more   
   > practical.   
      
   Why bother with air breathing, winged vehicles at all?  Why not consider a   
   conventional, rocket powered VTVL TSTO?  Such a design wouldn't even need an   
   altitude compensating engine (i.e. aerospike), since the first stage would   
   be optimized for low altitudes and the second stage for vacuum.   
      
   Jeff   
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