NP Mars Trilogy

[tbeshear]

Sorry -- I meant in science fiction, as far as I've read. I didn't think Clarke invented the concept.
  ----- Original Message ----- 
  From: Monte Davis 
  To: 'tbeshear' ; 'Daniel Cape' ; kelber at mindspring.com ; 'pynchon-l' 
  Sent: Saturday, September 19, 2009 4:46 AM
  Subject: RE: NP Mars Trilogy


   

   

  Tbeshear sez:

   

  Ø  Clarke introduced the idea of the space elevator in The Fountains of Paradise. 

   

  Konstantin Tsiolkovski published the idea of a "space tower" in 1895. He knew it was un-buildable, _gedanken_, but his point was the conceptual physics: IF it could be built, you could climb it at a comfortable pace, on foot or by elevator or whatever, acquiring a little bit more transverse velocity at each step as the tower swung around with the earth's rotation, until at about 23,000 miles you'd be moving at orbital velocity and could step off and float. (23,000 miles is geosynchronous orbit, in which a satellite stays over the same point on the equator. Tsiolkovski seems to have been the first to grasp that, too, as Clarke knew and acknowledged whenever people tried to credit him with it.) 

   

  In 1960, Yuri Artsutanov went most of the remaining conceptual distance by replacing the tower with a cable in tension. A  mass beyond geosync orbit - where it would revolve *faster* than orbital velocity for its altitude, and pull up/outward - would counterbalance the weight of the cable from orbit down to earth's surface. Much more feasible, as the cable doesn't buckle the way a tower would at even a small fraction of 23,000 miles, and many engineering materials are stronger in tension than compression (cf. suspension bridges). Artsutanov also had the crucial insight that you didn't have to do the full- size cable all at once, but could begin with a lighter fiber just strong enough to support itself, and then use travelers to "spin" additional fibers, as we build up the main cables of suspension bridges.

   

  Although the counterweight remained in most SF versions ("start by maneuvering an asteroid into geosync or Mars-synchronous orbit"), it isn't essential: the farther the cable itself extends beyond geosync orbit, the less mass you need at the far end. And if you can do a 23,000-mile cable in the first place, it's probably easier to just do a longer one than to go asteroid-wrangling.

   

  All this was much less fantastic than the original space tower, but still out of reach. Artsutanov had been thinking of the graphite "whiskers" discovered in the late 1950s, with the highest strength/weight known, but still not good enough. Steel, even diamond were right out: even tapering both ways from geosync orbit, they'd have to be impossibly thick and mass  millions or billions of tons. If you have the tech to put that much mass into space, you don't NEED a space elevator.

   

  The most recent step was the discovery c. 1990 of carbon nanotubes, stronger than graphite whiskers. (Mentioned in _Green Mars_ as handwaving, without detail.) They *might* just be strong/light enough to do the job (still some uncertainty about basic measurements) if they could be made flawless enough  and bonded to each other on an adequate scale. In principle, a thousand tons or so could do the job. That's what got the space elevator conferences going in 2002, and disseminated the idea that we're ready to go. In fact, there's a LOT of basic research still to do on growing carbon nanotubes, and a LOT of process engineering not even begun on turning them into reliable bulk material, It could easily take as much R&D investment and time as there was between the first transistor c. 1949 and an Intel multi-core CPU today. Space elevators are a seriously cool idea to get around the inexorable limits of rocketry (also perceived by Tsiolkovski back in the day), but if they happen it won't be soon. 
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