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The World's Longest Carbon Nanotube
Roland Piquepaille writes "As you probably know, carbon nanotubes have very interesting mechanical, electrical and optical properties. The problem, currently, is that they're too small (relatively speaking) to be of much use. Now, researchers at the University of Cincinnati (UC) have developed a process to build extremely long aligned carbon nanotube arrays. They've been able to produce 18-mm-long carbon nanotubes which might be spun into nanofibers. Such electrically conductive fibers could one day replace copper wires. The researchers say their nanofibers could be used for applications such as nanomedicine, aerospace and electronics."
That's na-NU, my man....
My understanding is that writers originally wrote the it as nano, and so in particular first season merchanise often used that spelling, but Robin Williams pronounced it as nanu.
File under 'M' for 'Manic ranting'
That puts it in the area of useable length for macro-sized application.
Well, they're still more slippery than wool, so that problem has to be solved too. But this is one piece of the puzzle, and it's very cool to see it coming along.
Although the PR person who wrote this obviously thinks this is a major breakthrough, these guys are using a method which was originally invented by Japanese researchers three years ago (google for "CNT super growth"). The Japanese guys have since focused on getting the fastest growth rate possible (I think it's about 0.2mm/min... if you want to figure out how many, many years it would take to grow a space elevator). There are lots of people working on improving this growth method, 18mm arrays may be the longest, but it seems to be in the same range as other people working on the "super growth" method. That doesn't diminish this research, rather it means that this method is very likely to work in the long run for industrial scale growth of nanotubes for materials (more simply, it's easily reproducible, and people want "nano-enhanced" golf clubs).
Isolated nanotubes have been grown longer than this (I've grown isolated nanotubes longer than this, and I'm not a growth specialist), as have bundles of nanotubes. This is the longest array of pure, aligned, continuous nanotubes.
From wikipedia.
This is not the record for longest tube ever grown. Groups have grown single tubes the size of their substrate wafers (4 inches usually). This group grew a long bundle of CNTs. In the field we call these 'forests'--imagine a lawn, but at the nanoscale. The blades of grass are the CNTs poking up off the surface.
Remember also that the figure of merit of a CNT when used for its mechanical properties is the growth defect density per meter, and even for the best growth techniques so far this ends up being a number like 1 every 10 microns (10^-6 m).
This means that for something such as a macroscopic cord, not only would one have to grow incredibly long CNTs, they would also have to be nearly defect-free in order to satisfy the (nearly magical) strength requirements attributed to them by many people.
It would be nice if people actually read up the subject before posting this garbage...
This is not "The World's Longest Carbon Nanotubes." It's the longest mass-producable parallel carbon nanotubes.
"Dictator Flakes. They WILL be delicious."
While I don't condone his actions in the past (that is, using /. to push more views to his site for personal gain), he doesn't link-through his site anymore. So now, he's just another submitter of crappy stories that generally give off wildly over-optimistic expectations of future possibilities.
You are in a twisty maze of processor lines, all alike.
There is a lot of hype here.
People don't seem to get this somehow. Yes, mass ratio matters. A lot. Let's look at LOX+Kerosene, a very typical combination in many ways. You get an ISP of about 3000 m/s in a medium-high performance vacuum engine (the case for most of the way to orbit). LEO takes about 9000 m/s of delta-v by the time you account for aerodynamic and gravity losses. That means the mass ratio of your rocket needs to be about e^(9000/3000) = e^3 = 20. So 5% of your rocket makes it to orbit. Yup, that sucks. LOX costs about $0.07/lb in bulk, kerosene about $0.30. So propellant costs are about $0.15/lb for propellant, or $3/lb of orbited mass.
Now lets look at the space elevator. Climbing to geosynchronous orbit is equivalent to about 8000 m/s of delta-v (roughly... don't have the exact number off hand and I don't feel like calculating it). From 1/2M*v^2, that's 32MJ/kg. That's about the energy you get from burning 6 kg of LOX-kerosene. So from an energy equivalence standpoint, you're using 6 kg of propellant worth of energy instead of 19 -- a factor of 3 improvement.
The problem with the space elevator is twofold. First, the required *form* of the energy is different. You can't just use cheap hydrocarbon fuels -- you have to convert it to electricity, and then get that electricity up to the elevator either by beaming it or along wires, and neither option is efficient in the slightest. In fact, by the time you turn the hydrocarbon fuel into electricity and then get it to the elevator car, you're under 50% efficient; being as high as 30% would take a lot of work and be quite impressive. But the rocket was 30% efficient! Space elevators are *not* particularly more efficient than rockets.
The second problem is the infrastructure of the space elevator -- the required capital investment for a certain payload rate (kg delivered per day) is higher than for the rocket (we won't even discuss non-reusable rockets). Even if you got the space elevator more energy-efficient than the rocket, this fact combined with the slower transit time, the geosynchronous orbit as the only one available, and the more complicated technological requirements, the rockets win.
Yes, the space elevator tech is harder. The ribbon itself and the beamed power are the obvious examples, but there are others. For example, the tires on the car that work against the ribbon -- you need tires that run at about Mach 3 and are good for 27000 miles. That's not even remotely easy. You need motors that have higher power to weight ratios than currently exist. Etc, etc, etc. Rockets, in comparison, are easy. Especially if you have space-elevator class building materials available -- at that point you can do SSTO with pressure fed rockets, and get rid of the pumps altogether -- the pumps being the hardest part of rocket engine development by far in a conventional design.
When people say that for space elevators you only have to provide the energy to climb up, and aren't wasting the energy carrying propellant, they often forget that it's actually a *lot* of energy to climb up, and that rockets are actually remarkably good at converting available chemical energy into exhaust kinetic energy -- some are better than 80% efficient by that metric.
Your idea of a space elevator is interesting, but very wasteful.
To make a far more energy efficient design you need to run the cars at constant speed. You also need to attach each car together. That way you can use the energy of the cars on the way down to help power the cars on the way up, much more like how a real elevator works. This means that the whole system requires a much more constant energy input.
This also does away with the idea that each car ever stops. It presents a problem of how you load and unload a moving system at the bottom but this is certainly a solvable problem. At the top you just have a fleet of small craft who dock with each car. Everything is moving in space anyway so all you need to do is match velocities, something the shuttle already does with the space station.
The mistake you seem to be making is trying to treat each car as separate entity rather than looking at the system as a whole. If you can do this then you can use the potential energy of the stuff (raw materials, people coming home, etc) you are bringing back rather than wasting it. This is why space elevators have the capability to be far more energy efficient than rockets ever can.
Now before everyone replies with all the problems, I know, its hard. The fact remains however that continuing on the current task of using semi reusable rockets (like the shuttle and it SRB's) then just letting the stuff we want to bring back fall is not an option. It wastes too much energy from the standpoint of bringing materials back.
Once I could have filled my post with numbers too, but I finished Physics (with Space Tech) several years ago now and have forgotten most of the maths needed.
I dont read
Carbon nanotubes have their strength in tension, not compression.
A self-supporting building based on nanotubes would have to be a tensegrity structure of some kind, where you'd have nanotubes pulling against something else that's relatively incompressible; maybe a diamond lattice. The tensions involved at the base of such a structure would be immense to keep the thing rigid enough to remain standing.
A space elevator, on the other hand, would rely purely on tension; the centrifugal effects of following the Earth's rotation are what keep it aloft -- that's the beauty of it. The tension forces -- greatest just below the geostationary orbit height -- would be large, but perhaps not as large as in the tensegrity structure.
You call this funding?"Orthodoxy is unconsciousness" - Orwell