From: henry@spsystems.net   
      
   In article <501f9880.0407140828.7e6f74bb@posting.google.com>,   
   Allen Thomson  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?   
      
   Good storable oxidizers are hard to come by, alas.  LOX has to be kept   
   very cold (not that hard to do in space, in principle, but the details are   
   a headache), hydrogen peroxide decomposes slowly (the loss of oxidizing   
   strength is relatively minor, but the tanks have to be vented to avoid   
   pressure buildup), and nitrous oxide needs to be kept either cold or under   
   high pressure (and its Isp typically isn't as good).   
      
   Chlorine pentafluoride, ClF5, is storable on about the same terms as   
   nitrogen tetroxide -- needs a bit of pressure -- and actually performs   
   quite a bit better.  The gotcha is that it is spectacularly intolerant of   
   even the most minor slip-ups in hardware design or operations, and once   
   started, a ClF5 fire just doesn't stop until the ClF5 is all gone.  (ClF5   
   is hypergolic not only with all fuels and all structural materials, but   
   with all normal fire-extinguishing agents...!  The recommended   
   firefighting procedure is "take cover at a safe distance".)   
      
   The fuel side is almost a detail by comparison.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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