Can Carbon Nanotubes Make Space Elevators a Reality?

[DaveC426913]

I'm looking for good links to stuff on space elevators, particularly for laymen, or even school-age students.

 

[berkeman]

What's a space elevator?

 

[DaveC426913]

You jest.

 

[stewartcs]

What's a space elevator?

http://en.wikipedia.org/wiki/Space_elevator

 

[DaveC426913]

Forgive me Berke. I could not bring myself to think you were asking seriously.

 

[berkeman]

Forgive me Berke. I could not bring myself to think you were asking seriously.

No worries. After seeing the wikipedia article, it is something that I'd heard of before, but when I saw you mention the term, I wasn't sure it was the same thing.

Orbital tethers
This concept, also called an orbital space elevator, geosynchronous orbital tether, or a beanstalk, is a subset of the skyhook concept. Construction would be a vast project: a tether would have to be built of a material that could endure tremendous stress while also being light-weight, cost-effective, and manufacturable in great quantities. Today's materials technology does not quite meet these requirements, although carbon nanotube technology shows promise. A considerable number of other novel engineering problems would also have to be solved to make a space elevator practical. Not all problems regarding feasibility have yet been addressed. Nevertheless, the LiftPort Group believes that the necessary technology might be developed as early as 2008[4] and that by developing the technology, the first space elevator could be operational by 2014.[5][6]

 

[DaveC426913]

I rue the fact that the name beanstalk has not caught on. It is both very accurate and whimsical.

 

[waht]

There is a nice fictional book about the construction of a space elevator "Fountains of Paradise" by Arthur C Clarke. It's just fiction, Clark basically rejuvenated the concept of a space elevator that was first brought up by a Russian scientist, forgot his name.

Today there is a lot of proposals and designs of various space elevators. The only problem is the material required. It has to be super light and super strong, and not be corrosive. I think we already have that in form of carbon nano-tubes. But we lack the industry, and know-how to efficiently manufacture hundreds of miles of cable.

There is dozens of clips on Youtube:

 

[FredGarvin]

Dave,
You do realize that the mere posting of a question will bring every space elevator whack-o on the net in here in no time.

 

[Ivan Seeking]

Dave,
You do realize that the mere posting of a question will bring every space elevator whack-o on the net in here in no time.

I never realized that this qualifies as subculture, but it probably does!

Are you implicity suggesting that the idea itself is cranky, or just that that it has a crank following?

 

[FredGarvin]

I never realized that this qualifies as subculture, but it probably does!

Are you implicity suggesting that the idea itself is cranky, or just that that it has a crank following?

I am implying that the following has a serious crank factor to it. Personally I think that the space elevator will never happen, even if we have thousands of plants turning out carbon nanotubes by the truckloads. However, like most things I am adamant about, I wait to be proven wrong.

 

[DaveC426913]

I am implying that the following has a serious crank factor to it.

I knew it had a big following, I'd no idea it was considered by some to be cranky.

 

[FredGarvin]

I knew it had a big following, I'd no idea it was considered by some to be cranky.

I call it cranky because of all of the people that have come on this board, it seems that 95% of them think that once we get carbon nanotube production going that it will be a simple matter of hooking them together with a tether and some motors.

 

[Ivan Seeking]

I am implying that the following has a serious crank factor to it. Personally I think that the space elevator will never happen, even if we have thousands of plants turning out carbon nanotubes by the truckloads. However, like most things I am adamant about, I wait to be proven wrong.

I tend generally to take the opposite view of things: I expect that it will happen until someone convinces me that it's not possible; and then I may or may not listen. But in this case, I recognize that the engineering challenges are daunting - the harmonics and wind shear forces being the ones the most come to mind for me.

 

[FredGarvin]

The structural problems are the ones that I think of as being the biggest hurdles as well.

 

[russ_watters]

Are you implicity suggesting that the idea itself is cranky, or just that that it has a crank following?

Is that two questions or one...?

 

[russ_watters]

But in this case, I recognize that the engineering challenges are daunting - the harmonics and wind shear forces being the ones the most come to mind for me.

As of today, engineering challenges are a distant second to the challenge of producing carbon nanotubes in such quantities. It's like discussing a bridge from New York to London - sure, there are engineering challenges, but the scale is what makes the very idea of building a bridge from New York to London asinine.

 

[Ivan Seeking]

As of today, engineering challenges are a distant second to the challenge of producing carbon nanotubes in such quantities. It's like discussing a bridge from New York to London - sure, there are engineering challenges, but the scale is what makes the very idea of building a bridge from New York to London asinine.

That doesn't seem like a fair analogy to me. I see it as being more akin to the transatlantic cable.

In what way does the scale of this concern you? We know that this is the issue but that can change quickly. It doesn't justify declarations of failure. Besides, Fred was assuming that we have production of nanotubes going.

 

[TVP45]

I tend generally to take the opposite view of things: I expect that it will happen until someone convinces me that it's not possible; and then I may or may not listen. But in this case, I recognize that the engineering challenges are daunting - the harmonics and wind shear forces being the ones the most come to mind for me.

In most industrialized countries, I think this would be close to impossible. Nobody would ever insure the construction and the environmental impact hearings would still be going on when the sun went dead.

 

[Ivan Seeking]

Nobody would ever insure the construction and the environmental impact hearings would still be going on when the sun went dead.

How is this any worse than the space program; say a mission to Mars?

 

[TVP45]

How is this any worse than the space program; say a mission to Mars?

A closer analogue might be building a nuclear power plant (OK, forget France - they make up for not liking Australian wine by being sensible about nuclear). My presumption is that a space elevator would involve a consortium of private industries and one or more governments. Imagine, if you will, a risk cascade analysis for a 50 km cable parting. What would a FMECA look like for hitting, say, Cleveland with that thing (sorry, Cleveland, but since you're trashing the Steelers this week, what goes around comes around)?

Now, if you could get a government to run, and fund, the whole thing, then you probably could get it off the ground in much the same way the space program works. After all, you could probably put the elevator in some out of the way place (maybe the Canadian provinces or the Sonora desert) and the effects of mishaps could be mitigated.

 

[russ_watters]

That doesn't seem like a fair analogy to me. I see it as being more akin to the transatlantic cable.

In what way does the scale of this concern you? We know that this is the issue but that can change quickly. It doesn't justify declarations of failure.

[separate post] How is this any worse than the space program; say a mission to Mars?

You are equating things that are several orders of magnitude different in scale. Ie, this is a much bigger project than a translantic cable - you are off by perhaps 3 order of magnitude. And there has never been a time since wires were invented (much less decades after they were invented) that they could only be produced in microscopic quantities and for thousands of dollars a gram. So production of carbon nanotubes will have to improve by, oh, I dunno, ten orders of magnitude in both cost and scale.

So I would say, as a rough guess, that a carbon nanotube space elevator would be around 10^23 times more difficult to do than a translantic cable. It puts it on similar footing with things like anti-matter propulsion.

In order to start with the assumption that 'anything is possible', like you said you do, you are assuming that we will discover new technology with the absence of any scientific basis for the assumption. Such assumptions are unscientific and wrong.

Besides, Fred was assuming that we have production of nanotubes going.

Fred said "even if". I'm not completely certain what he meant, but my position, if I were willing to let the first "impossible" go, would be "even if" we get past the first 'impossible', there is another one right behind it. But I'm not willing to let the first ''impossible' go.

BTW, I'm pretty sure you once suggested that it is best to start out with no assumptions. The 'anything is possible' assumption is the crank assumption that makes this a cranky subject.

 

[DaveC426913]

So I would say, as a rough guess, that a carbon nanotube space elevator would be around 10^23 times more difficult to do than a translantic cable. It puts it on similar footing with things like anti-matter propulsion.

That's silly. Antimatter propulsion is science fiction. We have NO form of antimatter propulsion. We do, on the other hand have the materials for a space elevator, even if the logistics and engineering challenges are fabulously difficult.

 

[russ_watters]

That's silly. Antimatter propulsion is science fiction. We have NO form of antimatter propulsion.

Correct. And far-out science fiction too. The Enterprise's "impulse engines" are fusion reactors. That, at least, is something that isn't just technobabble-gibberish. Antimatter? It is barely even concievable right now.

We do, on the other hand have the materials for a space elevator, even if the logistics and engineering challenges are fabulously difficult.

Not correct. The "challenges" posed by the materials far exceed any scientific/engineering endeavour ever undertaken by mankind. And that comes before the logistics and engineering challenges of building it. We can synthesize anti-matter and we can synthesize carbon nanotubes. And both on about the same scale.

What would you say about the feasiblilty of buidling a DNA strand to the Moon? The very words put together into a sentence are pretty much nonsensical, right? Right now, (and for the past few decades) that's where carbon nanotube production is.

It is silly.

 

[russ_watters]

Lets do a little cost/scale exercise. No one has done it yet, but let's assume that it would be possible sometime in the relatively near future for a manufacturing plant to produce 1 meter of carbon nanotubes per year using a gigawatthour of energy. And let's assume that a million strands would be strong enough to support a space elevator. The cable would stretch to 1.5 times geostationary orbit (60,000 km). (power costs about $.1/kwh)

How many plants and how long would it take to build and how much would it cost?

 

[DaveC426913]

Lets do a little cost/scale exercise. No one has done it yet, but let's assume that it would be possible sometime in the relatively near future for a manufacturing plant to produce 1 meter of carbon nanotubes per year using a gigawatthour of energy. And let's assume that a million strands would be strong enough to support a space elevator. The cable would stretch to 1.5 times geostationary orbit (60,000 km). (power costs about $.1/kwh)

How many plants and how long would it take to build and how much would it cost?

I'm not prepared to take those initial numbers for granted.

 

[FredGarvin]

Despite anything that can be said, there is one thing that can not be disputed at this point; there will need to be some major technological breakthroughs (not just advances) for the design process to even get kicked off. The thing that eludes most people is that it is all just a thought exercise at this point and will be for at least a few more decades (if not longer).

I would be a lot happier if half of the energy put into the space elevator ideas and notions was, in stead, put into the advancement of solar energy.

 

[russ_watters]

I'm not prepared to take those initial numbers for granted.

Well, yeah - they are optimistic. My point is that even with very optimistic assumptions about production, it's still Star Trek level science fiction.

 

[Integral]

You are equating things that are several orders of magnitude different in scale. Ie, this is a much bigger project than a translantic cable - you are off by perhaps 3 order of magnitude. And there has never been a time since wires were invented (much less decades after they were invented) that they could only be produced in microscopic quantities and for thousands of dollars a gram. So production of carbon nanotubes will have to improve by, oh, I dunno, ten orders of magnitude in both cost and scale.

So I would say, as a rough guess, that a carbon nanotube space elevator would be around 10^23 times more difficult to do than a translantic cable. It puts it on similar footing with things like anti-matter propulsion.

In order to start with the assumption that 'anything is possible', like you said you do, you are assuming that we will discover new technology with the absence of any scientific basis for the assumption. Such assumptions are unscientific and wrong. Fred said "even if". I'm not completely certain what he meant, but my position, if I were willing to let the first "impossible" go, would be "even if" we get past the first 'impossible', there is another one right behind it. But I'm not willing to let the first ''impossible' go.

BTW, I'm pretty sure you once suggested that it is best to start out with no assumptions. The 'anything is possible' assumption is the crank assumption that makes this a cranky subject.

Russ I seriously expect that you are pulling some numbers out of your A$$.

Does making up numbers make this a meaningful post? Perhaps you should stick to generalities.

 

[FredGarvin]

The only number that really requires estimation is the power required to produce the nanotubes.

Just for argument sake, let's say that a plant could make 1 nanotube the required length to get something into stationary orbit, let's say 1000 km, in 6 months. Let's also say that the power required is no more than a common household usage, let's say 20 kWh/day. Let's also assume that a bundle required for the space elevator requires 1 million individual tubes.

According to my calcs, that would equate to an energy (and only energy) usage of 3.6x10^9 \frac{kWh}{bundle} which equates to $360 M/bundle. In terms of the space program, that cost is not too exorbitant. However, does anyone have a handle on the cost for materials and equipment required to produce this stuff? I have no idea there.

However, looking at the time to produce, if there were 1000 factories churning out 1 tube 1000 km in length every 6 months, that still equates to 492 years to produce one bundle.

Like all engineering endeavors, we're already behind schedule.

 

[russ_watters]

Russ I seriously expect that you are pulling some numbers out of your A$$.

Does making up numbers make this a meaningful post? Perhaps you should stick to generalities.

Yes, I'm making them up and yes, they most certainly make for a meaningful post if they are educated guesses and illustrate the magnitude of the problem.

Ivan used the example of a translantic cable for comparison, but translantic cables are only something like 2,000 miles long, while geostationary orbit is 22,000 - and a translantic cable doesn't hold up its own weight and uses cheap, mass produced materials. It is important for him to understand that his example is wrong by many, many, many orders of magnitude. It doesn't actually matter he's off by 5 orders of magnitude or 10 (or 50), the point is the same: the position that a space elevator is anything but Star Trek level science fiction is absurd.

 

[russ_watters]

The only number that really requires estimation is the power required to produce the nanotubes.

Just for argument sake, let's say that a plant could make 1 nanotube the required length to get something into stationary orbit, let's say 1000 km, in 6 months. Let's also say that the power required is no more than a common household usage, let's say 20 kWh/day. Let's also assume that a bundle required for the space elevator requires 1 million individual tubes.

According to my calcs, that would equate to an energy (and only energy) usage of 3.6x10^9 \frac{kWh}{bundle} which equates to $360 M/bundle. In terms of the space program, that cost is not too exorbitant. However, does anyone have a handle on the cost for materials and equipment required to produce this stuff? I have no idea there.

However, looking at the time to produce, if there were 1000 factories churning out 1 tube 1000 km in length every 6 months, that still equates to 492 years to produce one bundle.

Like all engineering endeavors, we're already behind schedule.

Well, you are also making big assumptions about the capacity of a factory and the power usage. These look pretty energy intensive to me:

Carbon nanotubes can be manufactured using a variety of methods:

· Laser ablation uses a high-power laser to vaporise a graphite source loaded with a metal catalyst. The carbon in the graphite reforms as predominantly single-wall nanotubes on the metal catalyst particles.

· Arc discharge involves an electrical discharge from a carbon-based electrode in a suitable atmosphere to produce both single and multi-wall tubes of high quality but in low quantities.

· Chemical vapour deposition (CVD) is where a hydrocarbon feedstock is reacted with a suitable metal-based catalyst in a hot furnace to ‘grow’ nanotubes which are subsequently removed from the substrate and catalyst by a simple acid wash.

http://www.azonano.com/details.asp?ArticleID=1108

I'm also not sure how it is even possible to speculate how we could go from the current production levels to 40,000 km (not 1,000 km) every 6 months. Some more research, though:

NASA scientists have developed an SWCNT manufacturing process that does not use a metal catalyst, resulting in simpler, safer, and much less expensive production. Researchers used a helium arc welding process to vaporize an amorphous carbon rod and then form nanotubes by depositing the vapor onto a watercooled carbon cathode. Analysis showed that this process yields bundles, or “ropes,” of single-walled nanotubes at a rate of 2 grams per hour using a single setup.

NASA’s process offers several advantages over metal catalyst production methods. For example, traditional catalytic arc discharge methods produce an “as prepared” sample with a 30% to 50% SWCNT yield at a cost of approximately $100 per gram. NASA’s method increased the SWCNT yield to an average of 70% while significantly reducing the per-gram production cost. Additional research is needed to determine the physical characteristics of NASA’s SWCNTs.

http://www.fuentek.com/technologies/carbon-nantubes.htm#techdet
It doesn't say what "significantly" means, but for a starting point, we can try $10 per gram. (that's actually more production for less than I would have expected).


http://www.isr.us/Downloads/niac_pdf/chapter2.html
Here's a space elevator site that says carbon nanotubes are around 100x stronger than steel and 1/4 the density. I really should let the people proposing it can be done do the math to prove it (unless that site calculated the mass and I missed it), but maybe I'll come back later and do a cost estimate with what we now have...

 

[FredGarvin]

What I was trying to show was that, even with extremely "advantageous" number estimates for the production costs (which I know are way too low) that the production still has no hope of getting up to speed any time this century. Even if the process uses the power that a common household uses, the energy requirement is pretty darned large.

 

[Benzsk8]

PBS had a good special on it in layman's terms. Just google PBS + space elevator and you should find it. One of the big problems noted is the carbon nano tube structure which is the heart of the elevator.