From: henry@spsystems.net   
      
   In article ,   
   Oren Tirosh  wrote:   
   >> ...Transpiration-cooling   
   >> systems would have to worry about clogging of orifices by waterborne   
   >> debris, and if they used a porous skin, about it taking up water.   
   >   
   >If a reentry vehicle injects steam through a relatively large orifice   
   >in the center of the heat shield, will it form a protective sheath and   
   >have most of the effect of transpiration cooling without requiring   
   >lots of little pores?   
      
   In principle, yes.  You might need multiple orifices, but there is some   
   evidence that they can at least be fairly far apart.  The details are   
   poorly studied.  In particular, the failure modes of such systems have not   
   been looked at very hard.  This is the sort of thing NASA *ought* to be   
   spending research money on, and building flying demonstrators for.   
   --   
   MOST launched 30 June; science observations running     |   Henry Spencer   
   since Oct; first surprises seen; papers pending.        | henry@spsystems.net   
      
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