From: henry@spsystems.net   
      
   In article <5dcb47db.0307180214.508282ad@posting.google.com>,   
   Mike Miller  wrote:   
   >I've seen the thermal conductivities for dry sand (.35W/m*K, IIRC)   
   >and soil (0.16), so I can imagine regolith to be a good insulator.   
      
   Lunar soil conductivity is estimated at 0.015-0.03 W/m-K at 1m depth.   
   Note that this is *very* well compacted, packed harder than could easily   
   be achieved with power machinery.  The much fluffier top 1-2cm is around   
   0.0015 W/m-K.  Regolith that was excavated and then loosely piled on top   
   of, say, a shelter would presumably be somewhere in between.   
      
   >However, solid rock can have an order of magnitude higher...   
   >So, would a habitat buried in a "big" (mountain-sized or more) cold   
   >rock (200K, 1.5W/m*K) need supplementary cooling like a habitat   
   >buried under lunar regolith?   
      
   My guess would be yes.  If it's a substantial habitat, the rock in its   
   vicinity won't stay cold for very long.   
      
   Also, bear in mind that said rock will almost certainly be covered with   
   regolith.  You don't generally find large masses of exposed rock on the   
   lunar surface.   
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