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« Why I Didn't Vote For Kerry | Main | Like Dogs To Their Vomit »

No Space Elevators?

Maybe not:

Laboratory tests have shown that individual nanotubes can withstand an average of about 100 GPa, an unusual strength that comes courtesy of their crystalline structure. But if a nanotube is missing just one carbon atom, this can reduce its strength by as much as 30%. And a bulk material made from such tubes is even weaker. Most fibres made from nanotubes have so far had a strength much lower than 1 GPa.

Recent measurements of high-quality nanotubes have found them to be missing one carbon atom out of every 1012 bonds; that's about one defect over 4 micrometres of nanotube length1. Defects of two or more missing atoms are much more rare, but Pugno points out that on the scale of the space elevator they become statistically probable.

Using a mathematical model that he has devised himself, and which has been tested by predicting the strength of materials such as nano-crystalline diamond, Pugno calculates that large defects will unavoidably bring a cable's strength below about 30 GPa. His paper has been posted to arXiv2, and will appear in the July edition of the Journal of Physics: Condensed Matter.

Pugno adds that even if flawless nanotubes could be made for the space elevator, damage from micrometeorites and even erosion by oxygen atoms would render them weak. So can a space elevator be made? "With the technology available today? Never," he says.

This seems like kind of an oxymoronic statement, because "never" implies the technology available any time, not just today. I would think that devices that continuously repaired redundant cables at a molecular level could solve this problem, though they're not "technology available today." In any event, I remain an agnostic.

Posted by Rand Simberg at May 23, 2006 06:23 AM
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Hmmm... sounds very likely, sadly, although as you say, "never" is a long time. I still have some hope for Space Elevators.

It reminds me of the materials science "fuss" over ceramic fibres in the mid-80s. Everything was looking great until it turned out that the maximum length they could grow them seemed to be about 1cm and then it all fell apart. They were a key part of our sylabus in 1987 and out in 1988.

Posted by Daveon at May 23, 2006 07:37 AM

I remain an agnostic.

A sentiment I appreciate. But more to the point if this is genuine and a workaround can't be found it also is bad news for structural members, body armor and etc. The SE is just the biggest (and unlikeliest) candidate for CNT applications.

Posted by Brian at May 23, 2006 08:23 AM

We should worry about tethers now, elevators later. Try a few finesse plays rather than go for the hail Mary pass.

Posted by rjschwarz at May 23, 2006 08:46 AM

With the tubes losing 30% of their strength with one little carbon atom missing, I sure don't plan on trying one out anytime soon. Perhaps "never" is strong language, but it definitely sounds like they are a long way from probable.

Posted by gamer girl at May 23, 2006 08:51 AM

Body armor, lightweight spaceship parts, etc., are probably safe. Those applications use nanotubes in a composite or polymer as a reinforcing material, like rebar. So, large quantities of really short nanotubes are o.k. These applications also don't normally subject nanotubes to the same tensile stress as an elevator (I think even gunshots are far less stress, but I don't have numbers).

Suspension bridges and elevators may be hosed as applications, though.

Posted by Big D at May 23, 2006 09:08 AM

I guess that means we quit trying to get it right. If we encounter any problems, we have to shut down, cease and desist, go home and sulk.

That is certainly the spirit that got us out of caves, off the back of horses and onto the moon.

I hope in 5 or 10 years the writer wishes he'd NEVER written that statement.

Posted by Steve at May 23, 2006 02:00 PM

Nah, it means that we figure out how to use shorter nanotubes to make ultralightweight spaceships, while the nanoengineers work on increasing the strength.

Posted by Big D at May 23, 2006 07:43 PM

Also, I don't know the numbers offhand for comparison, but this does not necessarily invalidate elevators on other planets.

Posted by Big D at May 23, 2006 07:44 PM

Preface: Not a scientist, just a guy, who thinks this is all very cool.


Automaticaly the possibility of using nano-tubes in suspension bridges is impossible, automaticaly the use of nanotubes for anything more than small support functions like being an aggregate for porcelain body armor or some other such seems VERY pre-mature.

I used to climb rocks, I'm affraid of heights, so I made sure that we used 13 mil "cables"/ropes to start (they are friggen HUGE! in climbing terms) within a few weeks, and more experience I realized I was safe with a 7 mil rope over certain heights, and really never need more than 11, including rapid decent rapeling.

The point of this. the ropes I used were so well engineered, that a 13 mil rope could stand up to virtually anything I could deliver to it, even if it's damaged. same with 11, 7 mil is a bit more speciallized.

To remove the idea of nano-tubes being a good use for a building composite strikes me as silly, granted, the individual strand might lose 30% of it's strength, over a length of . . . whats the ratio of length to strength per average nano-tube failure?

If you properly weave the tubes in large enough numbers, after all, you would need at least MILLIONS of individual tube strands to build a standard GUIDE cable of steel, do you really need the individual strength of the tube at ONE point, to sustain a structure when the tubes will in fact not be individual structures that stand alone, but rather are a part of a system of co-supportive structures? Every weakness in one strand, will be ignored, and never strained because the rest of the strands will handle the forces applied to it.

All it says is that this new tech, the nano tube, must be designed with a 30% engineering oversight rather than a 15%, and still 30% oversight with nano, is still . . . . I don't know, how much less than all other materials?

I know I didn't put my words to proper use, but, a seemstress could correct this argument more easily than I, after all, thread consists of strands of material that AREN'T EVEN CONNECTED!!! The thread your clothes are sewn together with consists of strands of fabric, some of which are less than an inch long, but they still hold together thanks to the alinear connection the threads make, and they support eachother.

once again, I have a problem puting my point across, but think thread, hell, even think concrete, and glass, and the steel cables that DO hold up suspension bridges, a tiny nick in a steel cable basicaly steels ALL of it's ability to maintain a flexible strength, it is all of the other strands that hold it together.

Posted by Wickedpinto at May 23, 2006 10:25 PM

Sadly, the problem is a bit more intractable than that.

There are two operating issues which make this very different to steel. Firstly, the mass of the structure.

Unlike a bridge, the steel is support a defined load which is split over several different strands and supports. You could cut several supports in a suspension bridge and the bridge will survive, likewise a fero-concrete structure can take a lot of punishment before it will collapse. However, in space elevator, the mass of the strands is enormous, even a single strand is going to be non-trival - We're talking a 30,000km+ cable after all.

Secondly, the physics of the substance. On this scale, materials behave differently to composites such as steel. When you look at a steel "strand", it's really no such thing - it's essentially long(ish) pieces of steel cable wrapped around other pieces. We're not 100% sure of the material science of long carbon nano-tubes, but each "strand" will be supporting it's own mass and will not be atomically linked to it's neighbours like in steel.

This also leads to some interesting questions if you build large C60 structures. There's a lot of interesting effects you get in carbon structures at the atomic level, especially in relatively stable forms like graphite and diamond. I'd be really interested to know if the same problems exist in Carbon 60. If they do, and reading between the lines of this article, then they might, then while there will be plenty of great applications for this stuff. It wouldn't be safe to use it in this sort of application. Shame.

The problem is that unlike other conventional supports or structures, the mass of the cable itself is going to be significant. This is the reason we need an esoteric substance for a space elevator - conventional steel or concrete is simply too weak to support that much of its own mass.

Then you get into the very nature of the nano-tubes. You can't think of it like it's a simple nylon or steel strand. Wrapping more of them together won't necessarily solve the problem, and, given it's carbon you can get some really weird atomic effects happening in carbon lattices which can have disasterous effects - I'm personally very interested to know if the problems you get in graphite and diamond also apply to Buckyballs and tubes.

Posted by Daveon at May 24, 2006 05:27 AM

Wrapping nanotubes together would be intended not to just increase the strength in proportion to thickness, but transfer stress around failures. But you'd need a way to get adequate coupling between the nanotubes without weakening them too much.

For tube degradation, you'd also worry about cosmic radiation, not just atomic oxygen (which could in principle be protected against with coatings) or micrometeorites. Cosmic rays will penetrate any practical amount of shielding without difficulty, and dislodge or transmute carbon atoms.

Posted by Paul Dietz at May 25, 2006 05:40 AM

Would it be possible to make carbon nano hooks, and have them joined together to form a carbon chain?

Posted by Robert at May 27, 2006 10:58 AM

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