From: henry@spsystems.net   
      
   In article <41F15D3E.CD363FA6@optonline.net>,   
   David Cornell   wrote:   
   >It sounds like a nuclear power supply is required for anything more than   
   >a couple of hours on the surface.  Is that true?   
      
   Yes, there seems to be no good alternative for long-lived landers.  (Note   
   that there *are* ways to build RTGs which would be better than existing   
   designs, mind you.)   
      
   >Would the ability to send data directly back to Earth be worth the cost?   
   >Or would be better off with a Titan orbiter that could serve as a   
   >communications relay?   
      
   Much depends on details.  One big advantage of relay via an orbiter is   
   that a random surface location generally has a line of sight to Earth for   
   only about 8 days out of every 16, while an orbiter can see Earth once per   
   orbit.   
      
   The situation isn't *quite* as good as for Mars, because the very extended   
   atmosphere forces an orbiter to orbit a long way up, making communications   
   to a lander a bit harder and hampering orbiter remote sensing.  But on the   
   whole, a support orbiter is still a good idea.   
      
   >Given the possibility that a probe might land on liquid, solid, or   
   >swampy surface, would be be better of with a amphibious rover, or would   
   >we try to steer it to a suitable landing spot.  Both options seem hard.   
      
   Going for a good landing spot strikes me as a better approach, but it does   
   have its own problems.   
      
   One interesting option is a multi-spacecraft mission, with a staggered   
   arrival schedule.  You *can* adjust the arrival times, within limits, of   
   things launched in the same launch window.   
      
   First a small orbiter arrives.  It's primarily for communications relay,   
   but it also includes an infrared imager for global mapping.  (I say   
   "small", and I avoid loading it up with instruments, because getting it   
   into Titan orbit is going to be difficult unless it uses some rather   
   speculative technology, so it's going to start out mostly rocket fuel.)   
      
   A little later, after time for a quick mapping campaign, half a dozen   
   small landers arrive.  These are battery-powered like Huygens, although   
   more focused on descent imaging and brief surface surveys than on   
   atmosphere studies.  Penetrators might be worth considering as an   
   alternative to conventional landers.  They're targeted relatively late, to   
   bring them down on a variety of terrains selected from the imaging; the   
   orbiter not only relays their data back, it also determines their exact   
   landing locations.  They're scouts for the main lander.   
      
   And only after that, with landing site selection postponed until after the   
   scout reports are in, comes the long-lived main lander, which has active   
   navigation during reentry to do something approaching a precision landing.   
      
   >Would a hot air balloon or glider work in Titan's atmosphere?   
      
   Yes.  Another interesting option is a helicopter:  it can do both   
   controlled flight and multiple safe landings.   
      
   >What kind of equipment would be worth having?   
      
   The obvious things are surface mobility, multispectral imaging, and some   
   kind of material analyzer (with an arm to bring it to its targets, MER   
   style -- that way it can analyze things that can't easily be picked up).   
   --   
   "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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