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>>>>I think I first came across the idea of a space elevator in Arthur C. Clarke's novel "The Fountains Of Paradise". From what I remember, it seems like the major problem is finding a material that won't sag under its own weight when you make it into a cable that's thousands of miles long.

Gordon: Actually, the problem is just the reverse. A space elevator doesn't have to be stron enough to support it's own weight. It has to be strong enough to keep the "string" from snapping and hurling the counterweight (space station) off into space. The only part than can fall is the carbon nanotube tether cable(s). And because it's made of carbon, most of it will burn up in reentry. Because it would only have to be microns thick, it would be like a multi-thousand-mile long roll of toilet paper falling (unrolled), rather than some huge steel structure.

As for Clarke, yes, he and Charles Sheffield wrote novels with similar concepts the same year. But they weren't the first to com eup with the idea by a long shot. Here is my afterword from the novel:

The space elevator described in this novel may not be in the realm of science fiction much longer. “Celestial towers,” “beanstalks,” “sky hooks,” and others similar concepts have been discussed and refined for decades: from Konstantin Tsiolkovsky in 1895 though Yuri Artsutanov in 1960, Jerome Pearson in the mid-1970s, Sir Arthur C. Clarke's novel The Fountains of Paradise and Dr. Charles Sheffield's The Web Between the Worlds in 1979, Kim Stanley Robinson's Red Mars/Green Mars/Blue Mars trilogy in the '90s, and a study commissioned by the NASA Institute for Advanced Concepts (NIAC) and authored by Dr. Bradley Edwards in 2000-2002 . Various possible solutions to some obstacles have been proposed along the way, but others required future science to provide the answers.

Until recently, the biggest obstacle was finding a material that was far stronger and yet lighter than steel, to use as the cable material. Kevlar was the first step in this direction, yet it too fell well short of the necessary strength-to-weight ratio.

Finally, in 1991 electron microscopist Sumio Iijima discovered carbon nanotubes (CNTs). CNTs offered the strength-to-weight ratio necessary to make space elevators a practical consideration.

The largest remaining technical hurdles appear to be finding ways to produce mass quantities of carbon nanotubes and link them together into cables tens of thousands of kilometers long, and how to keep all the space junk orbiting Earth from colliding with the elevator. Beyond that is the larger issue of finding the funding and the will to undertake a task that would make the International Space Station program pale by comparison. Still, the NIAC study suggests that a feasible design could be constructed within the next fifty years. By the late twenty-second century, when this novel is set, the technical, financial, and sociological hurdles should have been resolved.

Many of the space elevator concepts used in this story come from the authors cited. Any errors in interpretation or extrapolation are mine.

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