I'm pretty sure the 100 GPa rating for a 1 meter wide cable already has a safety factor of 2 built in. If you wanted 3, then you could either go to 10 meters, or wait until you could manufacture a stronger (150 GPa) composite material.
You're right, you would have to do some serious lateral acceleration to get to the top. Luckily, this is spread out over a 1-week climb so the specific impulse required is not too great.
But actually, the lateral acceleration at the top of the elevator is one of the main selling points. By the time you reach the top of the elevator, you've got enough angular momentum that you can just let go and be thrown to the Moon or Mars for free.
Check the bottom of this page. Of particular note:
In any analysis of the environmental impact the possibility of a falling cable and the damage it will cause must be compared to the alternative which is continued use of rockets. During rocket use both pollutants from the burning fuel and from the re-entry of the spent rockets must be considered. For example, each Titan IVB has a dry mass of 65,000 kg, much of which ends up re-entering and burning up in Earth's atmosphere. The Titan IVB also burns roughly 500,000 kg of propellant. Our proposed 20 ton capacity cable has a mass of 750,000 kg. A strictly mass comparison is far from the proper comparison to make but it gives a rough idea of scales of the environmental impacts we need to compare.
I've seen this stuff... somewhere, and it looks just like black string.
There are some pictures of real carbon nanotubes in plexiglass containers available here, taken with my crappy digital camera at LiftPort.
Cool story: at one point some of this material, which looks more or less like soot, spilled onto the flat, seemingly smooth table top. After wiping it off, there was a permanent black smudge left on the table top that no amount of scrubbing would remove... some of the nano-scale CNTs had slipped down into the microscopic grooves and divots on the table surface!
Michael Laine (of LiftPort Inc.) told me that Edwards' Phase 1 presentation had much the same effect on him, and in fact it was what finally inspired him to pursue this concept full-time.
Apparently hecklers in the audience gradually converted and by the end were offering up resumes to work on the project.:-)
A few days ago here on Slashdot there was a link to an interview that The Onion AV Club was running with Arthur C. Clarke. I found it intruiging that (1) Clarke says that Fountains of Paradise is still his personal favourite of his published works, and (2) that he's hoping for it to be made into a film shortly.
Here's Fountains on Amazon (no affiliation) if you want to check out the reviews.
While there is a difference between achieving 100 GPa over very short lengths and over 100,000 kilometers, it's not as much as you might think.
The longest individual nanotubes we can reliably produce are on the order of a couple of centimeters. But once we have nanotubes on the order of a meter long, they will probably be sufficient to produce a long ribbon with sufficient loading on the nanotubes themselves.
The limiting factor is not the length of the nanotubes in a composite (beyond a certain point, anyway), but rather how effectively the nanotubes themselves can be made to bear the load. Nanotube exteriors are slippery, like graphite, so the challenge is being able to stick them together in a substrate the transfers load effectively between them.
For this, a process known as "functionalization" comes into play. This basically means adding small appendages to the nanotubes so that they have more traction within the substrate.
LiftWatch.org carries regular space-elavator news items. Here are some recent articles on CNT advances:
I was particularly interested in the last couple of paragraphs, regarding a possible film adaptation of Fountains of Paradise, and the fact that Clarke considers that his best/favourite novel.
Fountains was the first novel to incorporate the modern concept of a space elevator.
Personally, I'm hoping for Steven Spielberg. He did a terrific job on Minority Report. Between that, AI, and Taken, he's definitely on a sci-fi roll lately.
A space elevator is totally infeasible at the moment. It is absolutely safe to predict that none of us will see such an installation realized in her or his lifetime.
Um, moderators... please take a moment to reconsider why you thought the parent comment deserved a +5, Informative. To me, it just reads like a troll.
Such predictions are never absolutely safe. In the case of a space elevator, you must be aware of recent feasibility studies commissioned by NASA. Although some advances in CNT (carbon nanotube) composite strength are still needed, there is every possibility that these will occur in the next couple of decades, if not sooner.
Space Elevator R&D fits perfectly with the national space strategy. An enduring, heavy-lift system, with low amortized cost would of course be ideal. But regardless of whether one actually gets built or whether the concept even works, research dollars in that direction would be very well spent because of the great potential for spin-off products and materials.
This is a perfect opportunity to put a bug in their ear about the space elevator concept, as one/. poster has already done.
I'm glad to see so many space elevator stories on Slashdot lately. I think the actual feasibility of this idea is important to impress upon people. SE research has a considerable amount of NASA funding, the fruits of which where the Phase I & II NIAC reports mentioned in the parent post.
LiftWatch.org is a news/portal site dedicated to following this and other developments in space elevators and related technologies. Besides the main front page news, here are some handy links for the SE afficianado:
I've been trying to get Slashdot to add LiftWatch headlines as an RSS feed. If you find the site interesting, please let the/. editors know so that there can be a LiftWatch.org slashbox.
If the theory is probably wrong, then it's about as reasonable that the maximum could be higher.
I think that the original poster meant not that the theoretical maximum strength for CNTs was WRONG... just that there might be other factors, as yet undiscovered, which may also limit the maximum strength. It is much more likely that the maxiumum strength of CNTs will be LESS than 300GPa than it is the strength will be GREATER than 300GPa.
Also, a space elevator could be built with steel cables, if you had the money to lift it all into orbit.
Not true. Steel does not have anywhere near the tensile strength needed to support even its own weight from GEO. Steel has 5GPa max. Something closer to 100GPa is required for a space elevator.
The nanotubes are sticky and bond well with themselves. Read the article.
While this is true, for a sufficiently strong composite material we will also need the nanotubes to bond well to the substrate polymer. Although CNTs are attracted to each other, they tend to have featureless, smooth surfaces that don't bond well with other materials. The likely solution to this problem is a process called 'functionalization' which adds features -- small appendages -- to the CNTs so that there is more traction within the substrate. More work is required here, but some recent developments are encouraging.
Slashdot Mirror
Answer: Just two, but how did they get in there in the first place?
I'm pretty sure the 100 GPa rating for a 1 meter wide cable already has a safety factor of 2 built in. If you wanted 3, then you could either go to 10 meters, or wait until you could manufacture a stronger (150 GPa) composite material.
You're right, you would have to do some serious lateral acceleration to get to the top. Luckily, this is spread out over a 1-week climb so the specific impulse required is not too great.
But actually, the lateral acceleration at the top of the elevator is one of the main selling points. By the time you reach the top of the elevator, you've got enough angular momentum that you can just let go and be thrown to the Moon or Mars for free.
Check the bottom of this page. Of particular note:
There are some pictures of real carbon nanotubes in plexiglass containers available here, taken with my crappy digital camera at LiftPort.
Cool story: at one point some of this material, which looks more or less like soot, spilled onto the flat, seemingly smooth table top. After wiping it off, there was a permanent black smudge left on the table top that no amount of scrubbing would remove... some of the nano-scale CNTs had slipped down into the microscopic grooves and divots on the table surface!
Michael Laine (of LiftPort Inc.) told me that Edwards' Phase 1 presentation had much the same effect on him, and in fact it was what finally inspired him to pursue this concept full-time.
Apparently hecklers in the audience gradually converted and by the end were offering up resumes to work on the project. :-)
A few days ago here on Slashdot there was a link to an interview that The Onion AV Club was running with Arthur C. Clarke. I found it intruiging that (1) Clarke says that Fountains of Paradise is still his personal favourite of his published works, and (2) that he's hoping for it to be made into a film shortly.
Here's Fountains on Amazon (no affiliation) if you want to check out the reviews.
While there is a difference between achieving 100 GPa over very short lengths and over 100,000 kilometers, it's not as much as you might think.
The longest individual nanotubes we can reliably produce are on the order of a couple of centimeters. But once we have nanotubes on the order of a meter long, they will probably be sufficient to produce a long ribbon with sufficient loading on the nanotubes themselves.
The limiting factor is not the length of the nanotubes in a composite (beyond a certain point, anyway), but rather how effectively the nanotubes themselves can be made to bear the load. Nanotube exteriors are slippery, like graphite, so the challenge is being able to stick them together in a substrate the transfers load effectively between them.
For this, a process known as "functionalization" comes into play. This basically means adding small appendages to the nanotubes so that they have more traction within the substrate.
LiftWatch.org carries regular space-elavator news items. Here are some recent articles on CNT advances:
I was particularly interested in the last couple of paragraphs, regarding a possible film adaptation of Fountains of Paradise, and the fact that Clarke considers that his best/favourite novel.
Fountains was the first novel to incorporate the modern concept of a space elevator.
Anyone heard anything else about this news item?
Personally, I'm hoping for Steven Spielberg. He did a terrific job on Minority Report. Between that, AI, and Taken, he's definitely on a sci-fi roll lately.
Um, moderators... please take a moment to reconsider why you thought the parent comment deserved a +5, Informative. To me, it just reads like a troll.
Such predictions are never absolutely safe. In the case of a space elevator, you must be aware of recent feasibility studies commissioned by NASA. Although some advances in CNT (carbon nanotube) composite strength are still needed, there is every possibility that these will occur in the next couple of decades, if not sooner.
See What is a Space Elevator? for more...
Space Elevator R&D fits perfectly with the national space strategy. An enduring, heavy-lift system, with low amortized cost would of course be ideal. But regardless of whether one actually gets built or whether the concept even works, research dollars in that direction would be very well spent because of the great potential for spin-off products and materials.
This is a perfect opportunity to put a bug in their ear about the space elevator concept, as one /. poster has already done.
See this related story on LiftWatch.org.
That UPI article is actually a 3-parter. Here are all three parts at spaceref.com:
Also, here's the LiftWatch.org story.
I'm glad to see so many space elevator stories on Slashdot lately. I think the actual feasibility of this idea is important to impress upon people. SE research has a considerable amount of NASA funding, the fruits of which where the Phase I & II NIAC reports mentioned in the parent post.
LiftWatch.org is a news/portal site dedicated to following this and other developments in space elevators and related technologies. Besides the main front page news, here are some handy links for the SE afficianado:
I've been trying to get Slashdot to add LiftWatch headlines as an RSS feed. If you find the site interesting, please let the /. editors know so that there can be a LiftWatch.org slashbox.
I think that the original poster meant not that the theoretical maximum strength for CNTs was WRONG... just that there might be other factors, as yet undiscovered, which may also limit the maximum strength. It is much more likely that the maxiumum strength of CNTs will be LESS than 300GPa than it is the strength will be GREATER than 300GPa.
Not true. Steel does not have anywhere near the tensile strength needed to support even its own weight from GEO. Steel has 5GPa max. Something closer to 100GPa is required for a space elevator.
While this is true, for a sufficiently strong composite material we will also need the nanotubes to bond well to the substrate polymer. Although CNTs are attracted to each other, they tend to have featureless, smooth surfaces that don't bond well with other materials. The likely solution to this problem is a process called 'functionalization' which adds features -- small appendages -- to the CNTs so that there is more traction within the substrate. More work is required here, but some recent developments are encouraging.