Posted: Mon May 05, 2008 4:40 am
Keegan, I'm aware of the awesome tensile strength necessary to construct the ribbon and the current limitations on CNT length. But, I'm not sure we need 100,000 km CNT molecules to make an adequate ribbon. One millimeter tubes woven into a matrix would make a ribbon capable of supporting a modest elevator car. It's curious to me that as futuristic as a SE might seem, fusion powered SSTO's may leapfrog right past them in affordability. Or, maybe the combined technologies will create an earth to orbit system better than fusion or elevators alone could provide.
From Wikipedia...
Cable
The cable must be made of a material with a large tensile strength/density ratio. A space elevator can be made relatively economically feasible if a cable with a density similar to graphite and a tensile strength of ~65–120 GPa can be mass-produced at a reasonable price.
Carbon nanotubes would be a highly useful material for creating a space elevatorBy comparison, most steel has a tensile strength of under 2 GPa, and the strongest steel resists no more than 5.5 GPa, but steel is dense. The much lighter material Kevlar has a tensile strength of 2.6–4.1 GPa, while quartz fiber[citation needed] and carbon nanotubes[28] can reach upwards of 20 GPa; the tensile strength of diamond filaments would theoretically be minimally higher.
Carbon nanotubes' theoretical tensile strength has been estimated between 140 and 177 GPa (depending on plane shape),[28] and its observed tensile strength has been variously measured from 63 to 150 GPa, close to the requirements for space elevator structures.[28][29] Even the strongest fiber made of nanotubes is likely to have notably less strength than its components.
Improving tensile strength depends on further research on purity and different types of nanotubes.
Designs call for single-walled carbon nanotubes. While multi-walled nanotubes are easier to produce and have similar tensile strengths, there is a concern that the interior tubes would not be sufficiently coupled to the outer tubes to help hold the tension. However, if the nanotubes are long enough, even weak Van der Waals forces will be sufficient to keep them from slipping, and the full strength of individual nanotubes (single or multiwalled) could be realized macroscopically by spinning them into a yarn. It has also been proposed to chemically interlink the nanotubes in some way, but it is likely that this would greatly compromise their strength. One such proposal is to take advantage of the high pressure interlinking properties of carbon nanotubes of a single variety.[30] While this would cause the tubes to lose some tensile strength by the trading of sp² bond (graphite, nanotubes) for sp³ (diamond), it will enable them to be held together in a single fiber by more than the usual, weak Van der Waals force (VdW), and allow manufacturing of a fiber of any length.
A seagoing anchor station would incidentally act as a deep-water seaport.The technology to spin regular VdW-bonded yarn from carbon nanotubes is just in its infancy: the first success in spinning a long yarn, as opposed to pieces of only a few centimeters, was reported in March 2004; but the strength/weight ratio was not as good as Kevlar due to the inconsistent quality and short length of the tubes being held together by VdW.
As of 2006, carbon nanotubes cost $25/gram, and even a space elevator that did not reach GEO would have a mass of 20,000 kg. However, this price is declining, and large-scale production could result in strong economies of scale.[31]
Carbon nanotube fiber is an area of energetic worldwide research because the applications go much further than space elevators. Other suggested application areas include suspension bridges, new composite materials, lighter aircraft and rockets, armor technologies, and computer processor interconnects. This is good news for space elevator proponents because it is likely to push down the price of the cable material further.
http://en.wikipedia.org/wiki/Space_elevator
BS
From Wikipedia...
Cable
The cable must be made of a material with a large tensile strength/density ratio. A space elevator can be made relatively economically feasible if a cable with a density similar to graphite and a tensile strength of ~65–120 GPa can be mass-produced at a reasonable price.
Carbon nanotubes would be a highly useful material for creating a space elevatorBy comparison, most steel has a tensile strength of under 2 GPa, and the strongest steel resists no more than 5.5 GPa, but steel is dense. The much lighter material Kevlar has a tensile strength of 2.6–4.1 GPa, while quartz fiber[citation needed] and carbon nanotubes[28] can reach upwards of 20 GPa; the tensile strength of diamond filaments would theoretically be minimally higher.
Carbon nanotubes' theoretical tensile strength has been estimated between 140 and 177 GPa (depending on plane shape),[28] and its observed tensile strength has been variously measured from 63 to 150 GPa, close to the requirements for space elevator structures.[28][29] Even the strongest fiber made of nanotubes is likely to have notably less strength than its components.
Improving tensile strength depends on further research on purity and different types of nanotubes.
Designs call for single-walled carbon nanotubes. While multi-walled nanotubes are easier to produce and have similar tensile strengths, there is a concern that the interior tubes would not be sufficiently coupled to the outer tubes to help hold the tension. However, if the nanotubes are long enough, even weak Van der Waals forces will be sufficient to keep them from slipping, and the full strength of individual nanotubes (single or multiwalled) could be realized macroscopically by spinning them into a yarn. It has also been proposed to chemically interlink the nanotubes in some way, but it is likely that this would greatly compromise their strength. One such proposal is to take advantage of the high pressure interlinking properties of carbon nanotubes of a single variety.[30] While this would cause the tubes to lose some tensile strength by the trading of sp² bond (graphite, nanotubes) for sp³ (diamond), it will enable them to be held together in a single fiber by more than the usual, weak Van der Waals force (VdW), and allow manufacturing of a fiber of any length.
A seagoing anchor station would incidentally act as a deep-water seaport.The technology to spin regular VdW-bonded yarn from carbon nanotubes is just in its infancy: the first success in spinning a long yarn, as opposed to pieces of only a few centimeters, was reported in March 2004; but the strength/weight ratio was not as good as Kevlar due to the inconsistent quality and short length of the tubes being held together by VdW.
As of 2006, carbon nanotubes cost $25/gram, and even a space elevator that did not reach GEO would have a mass of 20,000 kg. However, this price is declining, and large-scale production could result in strong economies of scale.[31]
Carbon nanotube fiber is an area of energetic worldwide research because the applications go much further than space elevators. Other suggested application areas include suspension bridges, new composite materials, lighter aircraft and rockets, armor technologies, and computer processor interconnects. This is good news for space elevator proponents because it is likely to push down the price of the cable material further.
http://en.wikipedia.org/wiki/Space_elevator
BS