XPost: sci.astro.amateur   
   From: henry@spsystems.net   
      
   In article ,   
   Marc 182   wrote:   
   >you've just got to keep your radio, computer, electronics, and batteries   
   >warm, which I suspect the RHUs were positioned to do anyway.   
      
   The trick is keeping them adequately warm in a dense atmosphere at LOX   
   temperatures, while not frying them in space beforehand.  Just good   
   insulation almost certainly is not enough; the atmosphere is likely to   
   increase heat transfer enough that you'll need to either add electric   
   heat, or have some sort of variable heat leak which switches off during   
   descent.  It's feasible but it adds mass and complexity.   
      
   (While there are insulation types whose effectiveness is different in   
   atmosphere than in vacuum, unfortunately, the change goes the wrong way:   
   good in vacuum and bad in atmosphere rather than vice-versa.)   
      
   >But, of course, they never expected it to live for any length of time on   
   >the surface... or did they?   
      
   They weren't even sure it would survive impact (and on a really hard   
   surface, it probably wouldn't have).  The primary mission lasted three   
   minutes after impact -- just long enough for a few pictures and some   
   readings from the simple little set of surface-material sensors.   
      
   >I wonder what the thinking was when they slipped in the big batteries.   
      
   If memory serves, the requirement was to reliably complete the primary   
   mission with one battery cell failed.  That meant having some safety   
   margin against worst-case conditions *after* taking one cell out of the   
   picture.  The result, unsurprisingly, was that with all cells working and   
   conditions generally not too bad, there was a large reserve of energy.   
   --   
   "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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