From: henry@spsystems.net   
      
   In article <9edf6d40.0407211440.52d18f9d@posting.google.com>,   
   Jeff Greason  wrote:   
   >To pick the first example to come to mind, LOX and methane are   
   >readily space storable, *especially* as far out as Saturn.  And they   
   >have noticably superior performance to tetroxide/hydrazine.  But   
   >it's got no flight history, you need igniters for the thrusters...   
      
   Although interestingly enough, Cassini's maneuvering engines -- which   
   are basically Apollo SM/LM RCS thrusters -- have igniters for their   
   hypergolics!   
      
   There's a little central "preigniter" torch chamber, which gets fuel and   
   oxidizer flow about 3ms before the main chamber does (by hydraulic design   
   rather than valve sequencing), to heat and pressurize the main chamber   
   before flow through the main injector starts.  Without that, they had   
   violent, destructive hard starts.  Yes, with hypergolics!   
      
   When the propellants sprayed into vacuum in a cold chamber, they were   
   flash-cooled by partial evaporation, and the result was a three-phase   
   (gas/liquid/solid) mixture, quite cold, with an unpredictable and   
   generally quite long ignition delay followed by BANG!   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)