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Thursday, May 25, 2006
Doubts About the Space Elevator
One of the most intriguing and unusual ideas regarding space travel has been the proposal to build an elevator that could transport cargo and people into near-Earth orbit. The elevator would consist of a cable made of carbon nanotubes, structures that have incredible strength given their size. The cable would stretch from the Earth's surface to a satellite in geosynchronous orbit - about 60,000 miles high. When in place, one could simply ascend the cable, without need for rocket propulsion.

The cable, actually a ribbon of nanotubes about the thickness of a sheet of paper, and about a meter wide, would have to withstand a tension of 62 gigapascals (GPa)- which is roughly the tension that would be exerted on a rope by 200,000 people playing tug-of-war. Nanotubes have already been shown to be capable of withstanding nearly twice that amount, which have led many to believe that this is actually a viable project. A Dallas-based company founded by a former NASA researcher, Carbon Designs, has plans to build an operational elevator within three years (if they can raise sufficient funds).

But a recent paper in the Journal of Physics, reported in Nature, concludes that inevitable minor imperfections in the manufacturing process would lead to a significant and fatal weakness in the ribbon.
Laboratory tests have shown that individual nanotubes can withstand an average of about 100 GPa, an unusual strength that comes courtesy of their crystalline structure. But if a nanotube is missing just one carbon atom, this can reduce its strength by as much as 30%. And a bulk material made from such tubes is even weaker. Most fibres made from nanotubes have so far had a strength much lower than 1 GPa.
...even if flawless nanotubes could be made for the space elevator, damage from micrometeorites and even erosion by oxygen atoms would render them weak. So can a space elevator be made? "With the technology available today? Never"
Well, the entrepreneurs are not dissuaded, but it does seem that there are some new challenges to overcome.

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