Hi all,   
      
   As a long time observer of the Sci.Space.* groups, and of the space and   
   aerospace industry I'm have become tempted to call Scram jets and other   
   air-breathing solutions (including Sir Richard's noble attempts out in the US   
   Midwest) as SCAM-jets. They're a    
   neat way to keep engineers and scientists funded, but highly unlikely to ever   
   produce an actual useful product. See NASA X-33 program, and possibly Orion   
   and SLS as examples of this.   
      
   They all demand incredible technologies and enormous flight rates just to make   
   them look even vaguely economical. AS David Spain pointed out, that Henry   
   Spencer regularly points out, LOX is cheap, and TSTO operations and technology   
   is relatively well    
   understood.   
      
   Now the heat exchanger tech that Reaction Engines Sabre is supposed to use is   
   incredible. Someone stated that it had basically shrunk the technology and   
   machinery that used occupy an entire (large) building into a shipping   
   container. But its still    
   nowhere near light enough, or efficient enough to actually supply the Sabre's   
   thirst for oxidizer.    
      
   And the sticky question remains: if you've cooled and compressed enough   
   atmospheric oxygen to power your upper and out-of-atmosphere flight phase what   
   did you do with the other 80% of the atmosphere you processed. Note if you are   
   turning atmospheric    
   Oxygen into LOX you can't avoid producing Liquid nitrogen on the way. You make   
   LOX by compressing and cooling. Unfortunately LN always happens before LOX   
   because N2 liquidifies at higher temperature and lower pressure than O2. Back   
   on terra-firma the LN    
   generated from LOX production is shipped off to the dozens (if not hundreds)   
   of different industries that use it for making useful products, or cooling   
   stuff down real fast or real low. On your way to LEO you have to ditch it, and   
   that is just WAY TO    
   MUCH WASTE ENERGY being thrown away.   
      
   Of cause if you could find a method to turn the O2 and N2 into one of the   
   nitrous oxides and use that as an oxider instead... That might be interesting,   
   and fun to watch from a minimum safe distance. And the technology, if light   
   enough and efficient    
   enough to go into an aerospace vehicle would be a very welcome addition to all   
   sorts of manufacturing here on earth.   
      
   REgards   
   Frank   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)