From: henry@spsystems.net   
      
   In article <41fc999d.3999836@supernews.seanet.com>,   
   Derek Lyons  wrote:   
   >>...the low temperatures and low gravity produce a *very* extended   
   >>atmosphere which makes orbits below ~1200km -- half a Titan radius! --   
   >>unstable(*).  This makes gravity and magnetic measurements from orbit   
   >>almost useless [and radar hard]...   
   >   
   >No, it makes a case for special purpose flight to carry the low   
   >altitude sensors.   
      
   Yes, but it has to be *flight* -- as in, balloon or aircraft -- not orbit.   
   At the sort of altitude you'd really like for such sensors, a Titan orbit   
   is quite impossible.   
      
   Ideally you'd like to be down around 100km or so... at which altitude,   
   Huygens had already jettisoned its main parachute, for the sake of getting   
   down to the surface before its batteries ran out.  Circa 200km is probably   
   passable... at which altitude, Huygens had pretty much finished reentry   
   and was about to deploy its pilot chute.  You could learn *something* at   
   300km... which was about the altitude of peak reentry heating for Huygens.   
      
   No reasonable spacecraft design will let you orbit at any useful altitude,   
   or even dip down to such an altitude at the low point of an elliptical   
   orbit, for any useful length of time.  Maybe a highly aerodynamic   
   spacecraft, covered with TPS tiles and using nuclear propulsion for orbit   
   reboost, could do a magnetic survey of Titan.  I doubt you could make   
   radar work under those conditions, and there will surely be too much air   
   drag for useful gravity measurements.   
   --   
   "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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