From: henry@spsystems.net   
      
   In article <1111455556.992946.212240@f14g2000cwb.googlegroups.com>,   
     wrote:   
   >Doesn't Spitzer solve this problem now... or actually a harder   
   >problem?  It's got a tank of liquid helium that must be kept   
   >cold for its multi-year mission.   
      
   It solves it only in a loose sense.  With elaborate insulation wrapped   
   around a modest-sized tank, it gets boiloff rate down to the point where   
   it won't boil dry for at least a couple of years.   
      
   Liquid helium is harder than liquid hydrogen, yes.  But on the other hand,   
   liquid-hydrogen tanks for propulsion will be far bigger -- they will   
   dominate the vehicle in a way that Spitzer's tank doesn't -- and they   
   can't tolerate a lot of boiloff, and mass issues limit the insulation.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
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