From: mp1walsh@Adelphia.net   
      
   Zoltan Szakaly wrote:   
      
   > I am wondering if a rocket engine's performance in the atmosphere   
   > could be improved by changing the operating point, such as mixture   
   > ratio or chamber pressure.   
   >   
   > My understanding is that under identical conditions in the chamber and   
   > nozzle we will get less thrust in the atmosphere because of the air   
   > pressure acting on the outside of the rocket engine.   
   >   
   > I also think that in the atmosphere we should get higher pressures in   
   > the nozzle because the combustion gases expand to a higher pressure.   
   > This effect will partially compensate for the effect of the external   
   > presure.   
   >   
   > This picture gets more complex if there are feedback loops that   
   > maintain constant conditions.   
   >   
   > I think that if we maintained a higher pressure during atmospheric   
   > flight such as to compensate for the effect of the atmospheric   
   > pressure we could get a constant thrust and improve atmospheric Isp. I   
   > think that as we increase the pressure we will get improved Isp, and   
   > if the pressure is limited by the structural load on the chamber and   
   > nozzle, the structure would only care about the pressure difference   
   > and so the pressure could be raised.   
   >   
   > I know about the aerospikes etc, I don't think it is practical to make   
   > a variable geometry nozzle.   
   >   
   > Zoltan   
      
   Well, raising chamber pressure is exactly what they do to get good   
   sea level performance.  That is one of the reasons that the Shuttle   
   main engines operate at 3000 psi.   
      
   You need to look at any good rocket propulsion text because   
   this is something that is very fundamental.   
      
   Mike Walsh   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)