`Scientists and science fiction fans alike have big plans for carbon nanotubes; it has been hoped that a cable made of carbon nanotubes would be strong enough to serve as a space elevator. However, recent calculations by Nicola Pugno of the Polytechnic of Turin, Italy, suggest that carbon nanotube cables will not work.
[..] Laboratory tests have demonstrated that flawless individual nanotubes can withstand about 100 gigapascals of tension; however, if a nanotube is missing just one carbon atom, it can reduce its strength by as much as thirty percent. Bulk materials made of many connected nanotubes are even weaker, averaging less than 1 gigapascal in strength.
In order to function, a space elevator ribbon would need to withstand at least 62 gigapascals of tension.’