From: earlcp@idirect.com   
      
   "zoltan"  :   
      
   > If you could boost the Isp to say 1000 you would not need nearly as   
   > much power as 15GW.   
   >   
   > I have an experimental air breathing engine that generates about 1 MW   
   > of power in terms of  the heat output of the propane burnt. This engine   
   > has a 7 inch nozzle and an Isp of 4000.   
      
   No, you don't.   You have an air-breathing engine that at static workbench or   
   at a fraction of a mach speed appears to work that well.  What you don't have   
   is a supersonic engine.  As far as I know you still have not flown your   
   design to see how it performs at even a good fraction of a mach.   
      
   > To get to orbit at an Isp of 1000 you need a mass ratio of 2.5   
   > To get to orbit at an Isp of 400 you need a mass ratio of 10   
   > You could probably get the shuttle to orbit on 5GW received power.   
      
   GW is a rate of power flow, not a total sum.  That are other factors than   
   just mass-ratio.  That is why there are no beer-can size SSTO rockets being   
   built.   
      
   > Zoltan   
      
           Earl Colby Pottinger   
      
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