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Physics/Carbon nanotube space habitats

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Question
Hi! I read that carbon nano tubes can be used to build huge space habitats on the order of thousands of kilometers but I remember hearing that we can only produce really small amounts of carbon nanotubes like only a few tons a year and it's an expensive material to produce so do you believe that we can discover a way to make carbon nanotubes in quantities that would allow us to build a McKendree cylinder 460km in radius and 4600km in length? Or are carbon nanotubes as a material to build huge constructs of mostly an ''unobtainium'' because of the practical challenges?

Answer
Dear Mika:

Carbon nanotubes (CNTs) are a big part of what I research professionally.  The best answer I can give you is that we are getting better at making them - and we definitely manufacture more than a few tons a year at this point.  The issue is quality.  There is *a lot* of variation in CNTs that arise from manufacturing strategy and scale.  

For your question, in terms of application, the real issue will be energy - both to put the CNTs into space and to make them.  Most of our CNT bulk manufacturers use high temperatures and/or voltages to synthesize them.

Here is a page listing current CNT prices
http://www.cheaptubesinc.com/carbon-nanotubes-prices.htm#Industrial_Grade_Nanotu

Note that low grades are relatively cheap per kg when compared to the cost of putting a kg of anything into space (something like 5000 euros/kg) right now.  So the limiting factor right now is not the CNT cost, but getting things to space.

My personal experience leads me to believe that the way to do this will be to use solar or nuclear energy in space to do the production using carbon found on the moon or elsewhere.  How long until we have this ability? I am uncertain.  But we don't actually have many technical reasons why CNT based space materials could not be used extensively in the future.

I hope this helps.  

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Dr. Jeffery Raymond

Expertise

Materials chemistry. Materials science. Spectroscopy. Polymer science. Physical Chemistry. General Physics. Technical writing. General Applied Mathematics. Nanomaterials. Optoelectronic Behavior. Science Policy.

Experience

Teaching: General Inorganic Chemistry I & II, Organic Chemistry I & II, Physical Chemistry I, Polymeric Materials, General Physics I, Calculus I & II
My prior experience includes the United States Army and three years as a development chemist in industry. Currently I am the Assistant Director of the Laboratory for Synthetic Biological Interactions. All told, 13 years of experience in research, development and science education.

Organizations
Texas A&M University, American Chemical Society, POLY-ACS, SPIE

Publications
Journal of the American Chemical Society, Nanoletters, Journal of Physical Chemistry C, Journal of Physical Chemistry Letters, Ultramicroscopy Proceedings of SPIE, Proceedings of MRS, Polymer News, Chemical and Engineering News, Nano Letters, Small, Chemistry.org, Angewandte

Education/Credentials
PhD Macromolecular Science and Engineering (Photophysics/Nanomaterials Concentration), MS Materials Science, BS Chemistry and Physics, Graduate Certificate in Science Policy, AAS Chemical Technology, AAS Engineering Technology

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