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May 24, 2006

Challenges making bulk carbon nanotubes strong enough for a space elevator

Researcher predicts that carbon nanotubes will have trouble getting more than 30 GPa of strength 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. Using a mathematical model that he has devised himself, and which has been tested by predicting the strength of materials such as nano-crystalline diamond, Pugno calculates that large defects will unavoidably bring a cable's strength below about 30 GPa.

Bradley Edwards, whose space elevator feasibility study for NASA and a subsequent book have made him the most frequent spokesman for the space elevator project. Edwards, who is president and founder of the Dallas-based company Carbon Designs, shrugs off the controversy, and says that with adequate funding he could make cables at or above the 62-GPa benchmark in just three years. He suggests that the key step is carefully spinning long nanotubes together in a close-packed way, which encourages cooperative frictional forces that make the strengths of individual nanotubes less crucial.

I think the space pier concept is superior. Achieving the goal of very cheap launches to orbit without having and maintaining the maximum material strength. A space pier only needs 5 GPa strength material. M5 Fiber is that is already strong enough for a space pier

Space elevators on the moon and mars would still be easy. Long skyhooks could be made to take cargo from space planes going to 100km.
High Altiture Long Endurance platforms can be made better with progressively better tethers and climbers that are being developed for the space elevator

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