From: zenadsl6186@zen.co.uk   
      
   johnhare  wrote   
      
   > My personal opinion is that the most profitable launch system in the near   
   > term   
   > would be based on a HTHL launch assist platform capable of Mach 3-6 with   
   > staging at very high altitude and low dynamic pressure. Upper stage, dunno.   
      
   Let's consider the upper stage first, and work backwards. Say we want 10   
   tons in LEO. A mass ratio of around 4 is good, because we can get dry mass   
   to around 10% without expensive scrimping, leaving 15% of the gross mass for   
   payload. So the gross mass is 65 tons for our 10 tons of payload.   
   Nice'n'easy.   
      
   If a LOX/LH2 stage is used, with an isp of 440 and a mass ratio of 4, that's   
   6,000 m/s delta V. To get somewhere interesting you need to start at about   
   1600 m/s horizontal velocity and 100 km of height (second stage start at 100   
   km is good, no Q to worry about so you can leave the aerodynamic structure   
   mass in the booster, you get vacuum isp's, plenty of coast time for   
   separation, and so on).   
      
   So that's the target. 65 tons to 100 km altitude and 1600 m/s horizontal.   
   You can mess with that a bit, but somewhere in there is what's needed.   
      
   I don't think a pure airbreather will do that, at least not easily. But I do   
   think a HTHL airbreather with LOX/kero rocket boost could do it. Preferably   
   piloted, though the second stage needn't be man-rated.   
      
   Something like:   
   jet fuel 70 tons   
   rocket fuel/oxidiser 190 tons   
   2nd stage gross mass 65 tons   
   1st stage dry weight 110 tons   
   flyback fuel 15 tons   
      
   for a 450 ton GLOW, suitable for standard aviation-type runways. No pads,   
   just an extra hanger with LOX/LH2 supplies at an airport.   
      
   You can maybe even use the jet turbines as pumps for the rocket fuel. Or   
   part-burn fuel to run the jet engines when there is no air. Use the rocket   
   engines as RATO's. And so on.   
      
   --   
   Peter Fairbrother   
      
   BTW - I was looking at teeny jets recently, around the 100N size. They have   
   a T/W around 11, and exhaust velocities around 1150 m/s. Cost a couple of   
   kilobucks. But, they have radial compressors :(.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)