It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
originally posted by: GV1997
a reply to: theabsolutetruth
they have accounted for them and now where does anyting say they are infalliable. Try reading up on them before making pointless comments like thinking carbon nanotubes are somehow eletrically conducitve.
Try reading up on them before making pointless comments like thinking carbon nanotubes are somehow eletrically conducitve.
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. In particular, owing to their extraordinary thermal conductivity and mechanical and electrical properties, carbon nanotubes find applications as additives to various structural materials. For instance, nanotubes form a tiny portion of the material(s) in some (primarily carbon fiber) baseball bats, golf clubs, car parts or damascus steel 
As with any material, the existence of a crystallographic defect affects the material properties. Defects can occur in the form of atomic vacancies. High levels of such defects can lower the tensile strength by up to 85%.
Crystallographic defects also affect the tube's electrical properties. A common result is lowered conductivity through the defective region of the tube. A defect in armchair-type tubes (which can conduct electricity) can cause the surrounding region to become semiconducting, and single monatomic vacancies induce magnetic properties.
All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a property known as "ballistic conduction", but good insulators laterally to the tube axis. Measurements show that a SWNT has a room-temperature thermal conductivity along its axis of about 3500 W·m−1·K−1; compare this to copper, a metal well known for its good thermal conductivity, which transmits 385 W·m−1·K−1. A SWNT has a room-temperature thermal conductivity across its axis (in the radial direction) of about 1.52 W·m−1·K−1, which is about as thermally conductive as soil. The temperature stability of carbon nanotubes is estimated to be up to 2800 °C in vacuum and about 750 °C in air.
Another risk of structural failure comes from the
possibility of vibrational harmonics. The
Vibrational energy could build up to dangerous
levels and exceed the cable’s tensile strength.
Remedy: This can be avoided by the use of
suitable clammy systems within the cable, and
by scheduling travel up and down the cable
keeping its resonant frequency in mind. It may
be possible to dampen the resonant frequency
against the Earth's magnetosphere.
To better understand this particular challenge, I contacted Keith Henson, a technologist and engineer who has written about space colonies and related space engineering subjects for nearly four decades. In 1975, he co-founded the L5 Society, now known as the National Space Society. Henson, despite his enthusiasm for space colonization, is skeptical that a space elevator will ever get off the ground.
Why we'll probably never build a space elevator
"No current material exists with sufficiently high tensile strength and sufficiently low density out of which we could construct the cable," he told me. "There's nothing in sight that's strong enough to do it — not even carbon nanotubes."
Indeed, this is the handy piece of evidence that's conveniently touted as the wonder-material that will make space elevators a reality. No doubt, these structures are the strongest and stiffest materials yet discovered in terms of tensile strength and elasticity — a strength that results from the covalent sp2 bonds formed between the individual carbon atoms.
"The best that theorists can do right now is come up with a material that's about two-thirds the strength needed to make a practical elevator," Henson told me. "And that's a very, very short tiny tube."
The problem, says Henson, is that when the carbon bonds get loaded to such an extreme extent, the hexagonal bonds that exist in carbon nanotubes become unstable when converting to 5-to-7 member bonds."
"It's not unlike a run in a lady's stocking," he says.
Henson worries that the cable, when exposed to such a tremendous strain, will simply unzip. Based on some preliminary models, the strain on the tether could exceed 100,000 kN/(kg/m) — so the material will have to have an extraordinarily large tensile strength/density ratio. Even with nanotechnology, he argues, it may not be possible to build material that's strong enough for the job. "It's not immediately obvious what can be done about this," he added.
"The bond strengths are known and you have a very limited number of bond strengths you can use around carbon," he says. "You can go outside of carbon and use boron nitride — it doesn't save you anything in weight — but it would conceivably be more resistant to this unzipping thing." He notes that no one has made nanotubes out of boron nitride.
"So, while it may be theoretically possible to get the material, it still looks pretty unlikely owing to the strengths of the bonds involved... the strength just seems inadequate."
It's worth noting that not everyone agrees with Henson. According to Bradley Edwards, a former Los Alamos physicist who has started several elevator-related companies in recent years, carbon nanotubes are up to the task. Science writer David Appell explains:
Lubos Perek of the Astronomical Institute at the Czech Academy of Sciences has warned that gravitational tugs from the Moon and Sun, along with pressure from gusts of solar wind, will shake the cable. These unpredictable — and potentially violent motions — could veer the tether into satellite traffic or space debris (another serious problem we'll get into in just a bit).
Perek says the lack of resistance against buckling or bending will have a profound impact on the elevator's stability, both in its initial phase as a geostationary (GEO) satellite as well as in its operational phase as a "sling."
There's also the hazardous stuff in orbit to consider.
"Even if you solve those problems you still have another problem to deal with — and that's all the space junk and active satellites," says Henson. "You've got to find it all and clean it up — and then you have to install dodging capabilities in all the existing satellites, except for the ones in geosynchronous orbit."
Henson says violent impacts with the cable would be a regular occurrence, and that most satellites and junk would be fast enough to "vaporize six or eight feet of the elevator."
Creating satellites with dodging capabilities is not a big problem, he says, it's just that every pre-existing one would have to be retired or re-configured.
"But you've got to clean all the old junk out as well because you can't move the cable around in any practical sense of the term — and there's 6,000 tons of junk up there," he says.
Cleaning up all that stuff is possible, argues Henson, especially if you build a big laser in space.
"If you're going to build a laser in space, however, you'll be using so much energy that you should just go ahead and raise the stuff via hydrogen rockets in place of an elevator," he adds.
originally posted by: DjembeJedi
Since it has first been hypothesized the space elevator has intrigued me. The notion of leaving our planet (ground floor) on an elevator and reaching the (top floor) space is AWESOME! BUT it seems very 1950's in a way as well almost Jetsons-esc.
" Scientists at Penn State University in the US released a research paper last month that showed the way forward to producing ultra-thin "diamond nanothreads" that have a strength and stiffness greater than that of today's strongest nanotubes and polymers."
Here is the article from CNN explaining the advancement in achieving this ambitious goal!
My question to you all out in ATS is would you ride the elevator? If so how much would the ride be worth to you?
originally posted by: theabsolutetruth
a reply to: GV1997