[Lewis Thomson (OP)]

Aaron wants to know about space elevators...

I understand that current materials such as carbon nanofibers could, theoretically, be used in the construction of a space elevator, for the cable required.
I believe that carbon fibre nanotubes are capable of conducting electricity.  Given that the Earth’s ionosphere is highly charged, would the cable of a space elevator essentially act as grounding for the ionosphere creating a kind of short circuit?  If this is not the case would it be possible to extract energy from the ionosphere using the cable?

What do you think?

[wolfekeeper]

There's currently no known way to make carbon nanotubes that are strong AND long enough to reach geostationary orbit.

However, I went to a lecture by a guy that specialises in graphene (which is basically unrolled carbon nanotube). There's now a theoretical way to make defect-free monomolecular graphene in unlimited lengths using a vapour deposition technique. Unfortunately he calculated it would take several thousand years to make enough for a space elevator using this technique, and even then it would be far too lightweight to lift any signficant payload. The main use of this might be to make touchscreens or for semiconductors.

[Marika]

Currently, carbon nanotubes are the best material for the job from a structural standpoint. However, there are no carbon fibre orientations out there that are simultaneously strong enough, thin enough, long enough, and flexible enough for the job. There are actually international competitions for developing the best type of carbon nanotubes to use for a space elevator. Carbon nanotubes conduct electricity better than metals do. That being said, in the context of a space elevator it could be possible for the carbon nanotubes to become charged in the ionosphere, however it would not act as a grounding force. With the right system, carbon nanotubes could be used to transfer electricity gathered from the ionosphere. 

[evan_au]

Depending on their twist, carbon nanotubes can be metallic-type conductors or semiconductors.
Today's manufacturing techniques produce a random assortment of sizes and twists, so it is a mixture of both.
Unfortunately, if lightning struck a conductive space elevator cable, it is likely to do nasty things to it...
See: https://en.wikipedia.org/wiki/Carbon_nanotube#Electrical