Editing Space elevator (section)

==Materials==
A significant difficulty with making a space elevator for the Earth is strength of materials. Since the structure must hold up its own weight in addition to the payload it may carry, the strength to weight ratio, or [[specific strength]], of the material it is made of must be extremely high.

Since 1959, most ideas for space elevators have focused on purely [[Tension (physics)|tensile]] structures, with the weight of the system held up from above by centrifugal forces. In the tensile concepts, a [[space tether]] reaches from a large mass (the counterweight) beyond geostationary orbit to the ground. This structure is held in tension between Earth and the counterweight like an upside-down [[plumb bob]]. The cable thickness is tapered based on tension; it has its maximum at a geostationary orbit and the minimum on the ground.

The concept is applicable to other planets and [[Astronomical object|celestial bodies]]. For locations in the Solar System with weaker gravity than Earth's (such as the [[Lunar space elevator|Moon]] or [[Mars]]), the strength-to-density requirements for tether materials are not as problematic. Currently available materials (such as [[Kevlar]]) are strong and light enough that they could be practical as the tether material for elevators there.<ref>[[Hans Moravec|Moravec, Hans]] (1978). [http://www.frc.ri.cmu.edu/~hpm/project.archive/1976.skyhook/papers/scasci.txt ''Non-Synchronous Orbital Skyhooks for the Moon and Mars with Conventional Materials'']. Carnegie Mellon University. frc.ri.cmu.edu.</ref>

Available materials are not strong and light enough to make an Earth space elevator practical.<ref>{{cite web |last=Fleming |first=Nic |date=15 February 2015 |title=Should We give up on the dream of space elevators? |url=http://www.bbc.com/future/story/20150211-space-elevators-a-lift-too-far |access-date=4 January 2021 |publisher=BBC |quote='This is extremely complicated. I don't think it's really realistic to have a space elevator,' said Elon Musk during a conference at MIT, adding that it would be easier to 'have a bridge from LA to Tokyo' than an elevator that could take material into space.}}</ref><ref>{{cite web |last=Donahue |first=Michelle Z. |date=21 January 2016 |title=People Are Still Trying to Build a Space Elevator |url=https://www.smithsonianmag.com/innovation/people-are-still-trying-build-space-elevator-180957877/ |access-date=4 January 2020 |publisher=Smithsonian Magazine |quote='We understand it’s a difficult project,' Yoji Ishikawa says. 'Our technology is very low. If we need to be at 100 to get an elevator built – right now we are around a 1 or 2. But we cannot say this project is not possible.'}}</ref><ref>{{cite web |date=30 January 2018 |title=Why the world still awaits its first space elevator |url=https://www.economist.com/the-economist-explains/2018/01/30/why-the-world-still-awaits-its-first-space-elevator |access-date=4 January 2020 |publisher=The Economist |quote=The chief obstacle is that no known material has the necessary combination of lightness and strength needed for the cable, which has to be able to support its own weight. Carbon nanotubes are often touted as a possibility, but they have only about a tenth of the necessary strength-to-weight ratio and cannot be made into filaments more than a few centimetres long, let alone thousands of kilometres. Diamond nanothreads, another exotic form of carbon, might be stronger, but their properties are still poorly understood.}}</ref> Some sources expect that future advances in [[carbon nanotube]]s (CNTs) could lead to a practical design.<ref name="Edwards" /><ref name="Smitherman"/>{{Page needed|date=August 2024|reason=Lengthy document; please provide applicable page.}}<ref name="universetoday" /> Other sources believe that CNTs will never be strong enough.<ref>{{cite web |last=Aron |first=Jacob |date=13 June 2016 |title=Carbon nanotubes too weak to get a space elevator off the ground |url=https://www.newscientist.com/article/2093356-carbon-nanotubes-too-weak-to-get-a-space-elevator-off-the-ground/ |access-date=3 January 2020 |publisher=New Scientist |quote=Feng Ding of the Hong Kong Polytechnic University and his colleagues simulated CNTs with a single atom out of place, turning two of the hexagons into a pentagon and heptagon, and creating a kink in the tube. They found this simple change was enough to cut the ideal strength of a CNT to 40 GPa, with the effect being even more severe when they increased the number of misaligned atoms... That’s bad news for people who want to build a space elevator, a cable between the Earth and an orbiting satellite that would provide easy access to space. Estimates suggest such a cable would need a tensile strength of 50 GPa, so CNTs were a promising solution, but Ding’s research suggests they won’t work.}}</ref><ref>{{cite web |last=Christensen |first=Billn |date=2 June 2006 |title=Nanotubes Might Not Have the Right Stuff |url=https://www.space.com/2456-nanotubes-stuff.html |access-date=3 January 2020 |publisher=Space.com |quote=recent calculations by Nicola Pugno of the Polytechnic of Turin, Italy, suggest that carbon nanotube cables will not work... According to their calculations, the cable would need to be twice as strong as that of any existing material including graphite, quartz, and diamond.}}</ref><ref>{{cite web |last=Whittaker |first=Clay |date=15 June 2016 |title=Carbon Nanotubes Can't Handle a Space Elevator |url=https://www.popsci.com/carbon-nanotubes-cant-handle-space-elevator/ |access-date=3 January 2020 |publisher=Popular Science |quote=Alright, space elevator plans are back to square one, people. Carbon nanotubes probably aren't going to be our material solution for a space elevator, because apparently even a minuscule (read: atomic) flaw in the design drastically decreases strength.}}</ref> Possible future alternatives include [[boron nitride nanotube]]s, [[carbon nanothread|diamond nanothreads]]<ref name="SCIAM_DN" /><ref name="Xtech_DN" /> and macro-scale single crystal [[graphene]].<ref name="azom.com" />