From: earlcp@idirect.com   
      
   Jon Watts  :   
      
   > 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   
      
   You are right and I am wrong.  When I double-checked my reference and did a   
   google search the number I should have reported was ISP of 424.   
      
             Earl Colby Pottinger   
      
      
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