Slashdot Mirror
Space Elevators: Low Cost Ticket to GEO?
Crocuta writes "The current issue of Science
News features a cover story
that discusses the current developments in space elevator technology. NASA has been
working on such devices for many years, but private companies such as Highlift Systems are now jumping on the space
elevator bandwagon, no doubt seeing the huge potential profit in a low cost per pound
delivery system. PhysicsWeb has a somewhat
older, but much more technical article
on the formation and structure of the carbon nanotubes that form the basis of the proposed
tether cables. With a development like this, we could shoot entire boy bands into space and make
the world a better place."
This is somewhat a repeat...at least we mentioned the space elevator before and the plans of NASA.
And I'll say it again. I *love* the idea of a space elevator. But I do not see how it will reduce the cost of going to space as much as some people claim. The maintenance costs for the tower will be tremendous.
Life is like a web application. Sometime you need cookies just to get by.
what happens when the cable snaps?
As fascinating as it sounds, unfortunately, Congress will never fund such an endeavor -- as far as they concerned, space is a useless void that we now have no reason to explore after the death of the USSR.
The idea might be feasible -- I prefer the idea of a giant cannon/mass driver/gauss gun to shoot us into space myself -- but the idea of a 100,000km tube supporting an elevator is too farfetched to ever get funding, especially with increasingly conservative US administrations that would rather spend money launching rockets not into space, but into third-world cities, as well as European powers that have their own budget problems due to their social welfare systems that prefer to spend money on Earth and not in space.
Ah, so we should stiffle useful technological advances, and live in fear of terror until the problem magically goes away?
The universe is a big scary place; we won't have the pleasure fully discovering this if we crawl under our beds and hide.
So when to elevator tickets go on sale?
How many gazillion of billions do you think it will cost. If not by any accident, how many terrorists does it take to blow it up? There just is not and cannot be such big amount of capital tied into one physical place. It might be possible to build it - once, if you find someone who is ready to BURN that money. Someone who invested all his money into a dot.com in 1999 is worth economics nobel prize compared to this.
The "slingshot effect" is only useful for trajectory changes. It allows one to save fuel when changing directions. Due to conservation of energy, when you approach a planet and slingshot away from it, you end up with the same velocity on the way out as the way in. You will accelerate as you approach a planet, but you will decelerate the same amount on the way out.
If the system software were written in Erlang, that won't be a problem.
Of course, those kitten-fucking pigs'll use Java, dooming millions to an icy grave in the sky...
Why stop with one seemingly improbable concept?
Once the elevator is built, use it to haul pieces of an Orion craft to the top and assemble it there. When it's ready, let it go, flinging it out of Earth's magnetic field. Once clear, light it up and go see the solar system.
This way there's no radioactive contamination of the atmosphere, minimal risk while getting the "fuel" in orbit, and it's a handy way to get a crapload of plutonium out of our hair.
Saturn in fifteen years, anyone?
With reasonable men I will reason; with humane men I will plead; but to tyrants I will give no quarter. -- William Lloyd
Well, the free electrons in the ionosphere are a conductive layer that shields us from radiation. So, if you deplete it too much, you'll not only get free electricity, but you could probably get your xray taken just by going outside.
If I drive fast enough at the red light, it'll appear green.
Ok, as much as we all laugh at Lance, or whatever his name is, from N'Sync trying to go into space, I think it was moronic of everyone involved not to make sure this happened, that he got up there and back safely, and had one hell of a good time.
The entire space program has been gradually fading from world view, and particularly from the Western world. Yes, there are programs still going on at NASA and ESA and even in China, but it's nowhere near what was hoped for in the 1960s and 70s. Putting a high profile celebrity into space would bring a lot of attention back to the space program. Would it be fleeting? Of course. That's what media attention is nowadays. But it would probably enspire a lot young kids to go to space, just as the early US and Soviet astro/cosmonauts did nearly half a century ago.
I tried every decent and legal way I could think of to resolve the issue w/the business before I rented the chicken suit
Think of the space elevator structure as a 100,000-km-long highway that will require ongoing maintenance and repair," says Smitherman.
How unrealistic can an analogy be? If a crack forms in some remote stretch of interstate, there's no danger of the rest of the interstate system suddenly ripping away and falling into space. Repairs would have to happen instantaneously without ever breaking an almost unimaginable ribbon tension. And this wouldn't be a very rare occurrence, either, as the ribbon would present a surface area of five to eleven million square meters on each side (5 to 11.5 cm wide, 10^8 meters long). And remember that it's on the equator, which every piece of orbiting debris crosses twice during each orbit.
And the only mentioned solution for lightning strikes (one of which could be fatal to the ribbon) seems almost totally unworkable, and doesn't take into account that a 100,000-kilometer-high conductive tower would generate its own lightning. Remember the ill-fated (but educational) Space Tether Experiment? And the tether was only a mile long. A space elevator's ribbon would intersect a huge chord of Earth's magnetic field, including both Van Allen Belts. Seems to me that, even if the ribbon didn't immediately blow like a giant flash-bulb filament, you still couldn't get within a hundred yards of the base due to the continuous electrical discharge.
Don't get me wrong--I've dreamed about space elevators since I was a kid reading about Clarke's hyperfilaments, but the more I think about it, the more unworkable it seems.
One thing I never see mentioned by all these proponents of nanotubes as a structural material is that extrapolating the strength of nano-scale covalent bonds to macroscopic dimensions is overly optimistic. "Calculations suggest... based on flexibility... 100x as strong as steel" sure. There are all sorts of materials, if you remove all the defects on an atomic scale, that are super strong. But saying that it is inevitable that we can scale up something from 1 micrometer to 100,000 kilometers is a bit of a stretch. If you made the cable out of solid flawless diamond, it would be stronger than out of nanotubes, and we can already make bigger diamonds than we can make nanotubes. I think a space elevator would be great, but don't hold your breath. There are a lot of details to be worked out in the materials science area before it is really a possibility. But nanotubes do hold promise, just not as much as everyone here seems to think.
So yes, there are many challenges to overcome, but they all, fortunately, seem surmountable.
I know a few Native Americans who might disagree with your final sentence.
"You want a toe? I can get you a toe by three o'clock... with nail polish."
This is just impossible! :)
But seriously, I did read it. Well, really just the section about nanotubes, and if the rest of the paper is equally fallacious, I think that would serve as pretty conclusive evidence of the imposibility of the space elevator. Using a combination of an overestimate of the strength of nanotubes with an underestimate of their density, the author uses a strength/mass ratio that is twice as large as the UPPER bound on the strength of nanotubes (which is the ideal strength). In practice the ideal tensile strength is typically many times higher than the yield strength. In case you're wondering, this is based on density functional calculations I performed myself--far better than the crude estimates refered to in the paper. And yes, I did just check his source. It's a review paper that refers to an extrapolation of a strength based on a strain from a tight-binding molecular dynamics calculation which the authors recommend taking with a grain of salt.
On the experimental side, noone has yet (to my knowledge) produced a composite based on nanotubes which is actually particularly strong. Even if these composites are developed (and probably eventually nanotube composites will surpas carbon fiber composites), they are guaranteed to pay a major hit in strength/mass due to the mass of the epoxy. Look for more like a factor of two over carbon fiber composites, rather than the factor of 50 or so advertised.
As mentioned in the paper, the mass of cabling needed is extremely sensitive to the strength/mass ratio. I don't know the relation (since I haven't looked up the Pearson paper), but he mentions that if you diminish the strength/mass ratio by a factor of 50 (using kevlar) from his fictitious nanotube ratio, the mass goes up by about a factor of 100,000. With an overestimate of the strength of nanotubes of at least a factor of two, probably much more, it seems highly unlikely that the cost of the elevator (already estimated to be rather high) will be within reason, and for all I know there may similar "rounding up" going on in the rest of the paper.
I'm a huge space enthusiast. Huge. I love just about anything that promises to bring the cost of space access to a reasonable (read: below $200 per kilogram) levels. I've been following the X-Prize competition with great interest.
That said, I can't get behind this space elevator push. First, the economics of it won't scale to meet a wide range of demand fluctuations. What if you build it and then find out that demand for it is only a tenth of what you had predicted? There's no way to scale down the sunk costs involved--it's an all or nothing sort of proposition.
Second, it would represent a prime terrorist target. No set of defensive systems could hope to cover against every possible means of attack. Missiles, bombs, lasers, and who knows what else. And we haven't even covered the subject of action by a hostile nation-state, which could presumably marshall far more impressive resources to the task of bringing down a cable.
Third, it represents completely unproven technology. Better to go with a multistage rocketplane or some variation on that theme. Design one that can be built with the equivalent of off-the-shelf parts and build it with a multi-purpose role. A launch vehicle that could also effectively double as a system for high-speed transoceanic delivery would have great commercial and military applications, and would be developed that much more quickly and economically.
In short, the space elevator is a nifty idea in many respects, but it won't happen until the construction of such a system is relatively trivial. When one business guy turns to another and says: "You know, we're paying a lot of money for pilots for our launch vehicles. Maybe we should just build an elevator and get some high school kids to run it."
In a world without walls, there is no need for Windows.
One of the papers on their talks about the high about of energy a climber will require and how the energy should be transmitted by laser (as nanotubes are very good conductors the resistance over that huge distance is just too much). Anyways there is absolutly no talk about conserving energy. As technically if you had a climber at the top, and assuming it used some sort of rollers to climb up and down. The energy generated by the rollers on the way down should be the same energy required to get back up. (Minues electrical resistance and stuff) Is there any way to save this huge about of energy? It seems such a waist to not atleast try.
Also, the plane could only hit a few miles up. The 'elevator' is more a suspended rope. All they'd have to do would be to extend the cable down further. This would probably also be done for 'routine maintenance'.
I don't read AC A human right
So of course, this being Slashdot, I get flamed and modded down by geniuses who don't know a fucking winking smiley when they see one.
Sigh... well, not like it matters. Excellent minus 2 is still Excellent, in all probability. And if not, well, it still doesn't matter.
My deviantArt site