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There's a flaw in our plan to build a space elevator

Carbon nanotubes aren't strong enough to make a space elevator

Bad news for sci-fi enthusiasts. Chinese nanotechnologists have calculated that the carbon nanotubes are nowhere near strong enough to build a space elevator out of.

In case you're unfamiliar with carbon nanotubes, they're a "wonder material" made up of carbon atoms arranged into hexagons that make up a tube.

They have weird and exciting electronic, magnetic and mechanical properties - including a tensile strength 100 times greater than steel with only one-sixth the weight.

That has lead some to suggest they could be woven into a fibre that would be strong enough to stretch into space, creating a 'space elevator' that could quickly and cheaply ferry goods and people into orbit.

Unfortunately, the carbon nanotube fibres that we've made so far are about a hundredth as strong as they should be. To find out why, Feng Ding from Hong Kong Polytechnic University lead a team that simulated what's happening at the nanoscale.

Weak Points

They built a model of a carbon nanotube with just one atom out of place - turning two of the hexagons into a pentagon and a heptagon. In tests, this tiny fault acted as a weak point, snapping much more easily than the adjacent hexagons.

Once it broke, the resulting strain on the rest of the structure was enough to totally unravel it.

With just one fault of this kind, the theoretical maximum tensile strength of a nanotube was cut from 100 gigapascals to just 40, with the effect even more severe when more faults were introduced. It's thought that a tensile strength of 50 gigapascals would be the minimum required for a functioning space elevator.

"Only carbon nanotubes with extreme quality are able to retain their ideal strength," Ding told New Scientist. "Most mass-produced carbon nanotubes are highly defective, and high-quality carbon nanotubes are hard to produce in large quantity."

Ding added: "Unless great breakthroughs on carbon nanotube synthesis can be achieved, using carbon nanotubes to build a space elevator would be extremely challenging."

He's right. A working space elevator would require 22 miles of carbon nanotube fibre without a single atom in the wrong place.

In space, where radiation and solar winds become a factor, that's pretty much an impossibility. Ah well - for the time being it looks like we'll have to stick with SpaceX's reusable rockets for getting things into space instead.

  • Duncan Geere is TechRadar's science writer. Every day he finds the most interesting science news and explains why you should care. You can read more of his stories here, and you can find him on Twitter under the handle @duncangeere.

Image credit: Liftport // CC BY 3.0