6647b6e3   
   From: nebusj-@-rpi-.edu   
      
   allbell@ctc.net writes:   
      
   >On May 14, 5:00 pm, nebu...@-rpi-.edu (Joseph Nebus) wrote:   
   >>         I'm sorry that more urgent issues have been keeping me from   
   >> posting regularly but on the bright side I have 145 pages done of a   
   >> second textbook that will hopefully make my plumage more interesting   
   >> to potential employers.   
      
   >Did you write that book about "Vorticity, Statistical Mechanics, and   
   >Monte Carlo Simulation"? If so, wow. How many celebrities have people   
   >who can write statistical mechanics textbooks in their active fan   
   >base?   
      
   	I did indeed.  Well, I co-wrote it.  There's actually some of   
   my doctoral thesis which can be made out in there, although it's much   
   more readable in that.   
      
   	I expect there's a lot of celebrities with fans like that,   
   though, particularly comic celebrities.  (Comedy seems really well-   
   suited to draw mathematically-oriented minds.)   
      
      
   >>         The real problem is making a cable lightweight and strong   
   >> enough for the task.  While a couple materials with the right weight   
   >> and strength characteristics exist, there aren't yet ways known to   
   >> make cables of those materials *nearly* long enough.   
      
   >I thought the other problem was that breaking the elevator would be a   
   >really good way to kill people.   
      
   	Oh, no, not at all.  If a space elevator should be possible at   
   all, it'll have to be an extremely lightweight fiber from the ground up   
   to space.  Assuming one wants to keep the tension throughout the cable   
   constant, which seems desireable, the result is the cable growing thicker   
   with altitude.   
      
   	The result is the cable near the ground would need to have the   
   sort of density of graphite.  If the cable were snapped and it were to   
   fall, there'd be almost like dust scattering on the ground.  A snapped   
   cable would tend to have a low terminal velocity.  (And since a space   
   elevator is best-built near the equator, well, look how much of the   
   equator is densely populated or even anything but ocean.)   
      
   	Stuff higher up on the cable might be dropped into the Earth's   
   atmosphere by such a snapping, but payloads being brought up to orbit   
   would presumably have few people, and they'd most likely be designed to   
   handle a drop like that anyway since it is an obvious potential failure   
   result.   
      
   	I am a fan of the concept, mind you, as I think it's a very   
   promising and clever idea.  But it has got the major problem that we   
   just don't have a cable material we can produce that's got the strength   
   to weight ratio.  That's not an impossible problem, of course, and to   
   solve it would indeed be useful outside the space elevator project, but   
   it is good reason for responsible skepticism.   
      
   --   
   								Joseph Nebus   
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