From: schillin@spock.usc.edu   
      
   thomsona@flash.net (Allen Thomson) writes:   
      
   >gherbert@gw.retro.com (George William Herbert) wrote   
      
      
   >> Tetroxide and hydrazine store very nicely.  Many very long duration   
   >> spacecraft have used them.   
      
   >Slightly idle question: are there other oxidizer/fuel combinations   
   >that have comparable storabilities and Isp?   
      
      
   WFNA (White Fuming Nitric Acid) and the hydrocarbon or alcohol of your   
   choice fits the bill, assuming you stick to the short list of materials   
   immune to WFNA.  But it's only comparable to N2O4/N2H4, rather than   
   clearly superior, in storability and performance.  The world picked   
   the latter pair for second-order reasons and it's probably not worth   
   reinventing the wheel for at best marginal gains.   
      
   Chlorine Trifluoride and Chlorine Pentafluoride are storable oxidizers   
   that give very high performance with hydrazine.  And cost a fortune,   
   and kill anyone who gets a whiff of them.  They keep cropping up in   
   studies, with some metal bent and some tests done, but nothing has flown.   
      
   In light of the obnoxiousness of the above, there's been a fair bit of   
   work lately with HAN (Hydroxyl Ammonium Nitrate) based oxidizers and   
   monopropellants, which are safe and non-toxic and nicely storable and   
   offer good performance.  But making reliable engines to burn them, is   
   turning out to be trickier than expected.   
      
   If you're willing to take a ~20% performance hit, Nitrous Oxide and   
   Ethane a la the XCOR teacart engine looks pretty good across the board.   
   Plus, in the right temperature range it's self-pressurizing.  But, there   
   is that performance hit, and a consequence of self-pressurization is that   
   your tanks may be heavier than you wanted for a low-performance system.   
      
      
   Nothing yet that is a clear win over hydrazine and nitrogen tetroxide,   
   which is why Cassini and everyone else uses hydrazine and nitrogen tet.   
      
      
   --   
   *John Schilling                    * "Anything worth doing,         *   
   *Member:AIAA,NRA,ACLU,SAS,LP       *  is worth doing for money"     *   
   *Chief Scientist & General Partner *    -13th Rule of Acquisition   *   
   *White Elephant Research, LLC      * "There is no substitute        *   
   *schillin@spock.usc.edu            *  for success"                  *   
   *661-718-0955 or 661-275-6795      *    -58th Rule of Acquisition   *   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)