From: First_Last@hp.com   
      
   Earl Colby Pottinger  wrote:   
   > gewi001@phy.auckland.ac.nz (Greg) :   
      
   > > "Horatio."  wrote in message   
   > > news:...   
   > >   
   > > >There would be a payoff in reliability due to the simplicity of the   
   > > system.   
   > >   
   > > I've never considered solids that simple. Sure thay look simple, but   
   > > try making one, then try making a big one.   
   > >   
   > > To first order approximation a solid is a pressure feed liquid with a   
   > > oversized combustion chamber(and all that it implies) and under   
   > > performing fuel combinations. And i left out the part were its kinda a   
   > > big stick of dynamite. Hybrids are better, but SSTO will be a liquid   
   > > fueled rocket.   
   > >   
   > > Solids are best left for the military applications thay were orginaly   
   > > devloped for.   
   > >   
   > > IMHO of course.   
      
   > Would like to point out that H2O2(liquid) and AlH3(solid) has a ISP over   
   > 550s.  This suggest a hybrid can be a SSTO.   
      
   >                  Earl Colby Pottinger   
      
   That seems difficult to believe, are you sure of that number?  I   
   plugged it into my handy-dandy Air Force ISP calculator and the best I   
   could get was around 490 (still pretty amazing) and that was at   
   ridiculous chamber pressure and expansion ratio (Pchamber = 5000 PSIA,   
   Pexhaust = .001 PSIA).  At more rational parameters (Pchamber = 1000   
   PSIA, Pexhaust = .1 PSIA) I get "only" 439 seconds, still pretty   
   respectable for a dense propellant combination (density=1.436).  I   
   tried it with oxygen instead of H2O2 and it did worse not better   
   (429s, density=1.287 with Pchamber=1000 PSIA, Pexhaust=.1 PSIA).  I'm   
   not sure why LO2 is worse than H2O2, perhaps a higher average   
   molecular weight exhaust and not enough gaseous products to suck the   
   heat out of the (solid) Al2O2?  The exhaust temp of the AlH3/O2 combo   
   is really high (2440 K).  In both cases there is quite a bit of H2 in   
   the exhaust.   
      
   Jon Watts   
      
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