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Space Elevator An Impossible Dream?
bj8rn writes "Three months ago, the dreams of a space elevator finally seemed to be coming true after a successful test. An article in Nature, however, suggests that there's reason to be pessimistic. Ever since carbon nanotubes were discovered, many have been hoping that this discovery would turn the dream into reality. Pugno, however, argues that inevitable defects in the nanotubes mean that such a cable simply wouldn't be strong enough. Even if flawless nanotubes could be made for the space elevator, damage from micrometeorites and even erosion by oxygen atoms would render them weak. It would seem that sci-fi will never be anything other than what it is: a fiction."
It would seem that sci-fi will never be anything other than what it is: a fiction.
Never? That's a very, very long time. I would never bet against never. Never always wins. (Especially if you believe in an infinite universe.)
Just have 2 stations. One on earth, one in orbit. In between the two would be nothing but space.
Have the station on earth "launch" the "elevator" and the station in space "catch" it.
Reason #0 to be pessimistic: A "successful test" isn't a climbing robot. The climbing robot isn't the hard part of the problem. The hard part of the problem is the materials science.
Nor is it the sort of discoveries we've seen in the materials side of the equation; fibers measured in millimeters. That's not a prototype, it's just basic research. Interesting basic research, worthy basic research, and good basic research to be sure, but it's not a demonstration of practicality by any stretch of the imagination.
When someone builds a small footbridge out of these things, I'll be interested. When you can scale that to a mile-long suspension bridge that supports two lanes of traffic in each direction, I'll be optimistic.
OK, the summary is ridiculous here. It assumes that because one method of making a space elevator might be impossible, that it can't be done, ever in any way.
There is so much that we don't know about the physical universe, that to even say we are beginning to understand what is possible is silly. Faster than light travel? Possible or not? As far as we have observed, not. Does that mean it's impossible? NO! We aren't even sure what time/space is, how can we say what is and isn't impossible? Is a space elevator impossible, just because this one method might be impractical? NO!
Somehow I wonder if the submitter was just trying to sound sensationalistic to make sure his story got accepted. And I just fell in his trap. Oh well. He did seem rather gleeful about the whole thing, though.
Qxe4
Sorry for being slightly off topic, but as a non physicist, I've always wondered why the other seemingly obvious problems with such a device are never really considered problems. I am thinking of storm type winds blowing it off balance or making it resonate, the danger to aeroplanes, the disastrous consequences of breakage, etc. Why aren't these problems?
This has already been addressed by Liftport, the company actually doing the work here:
I've discussed the article with a couple of CNT researchers, and they say that they're not convinced by the paper. My attitude is that we have to wait and see what really happens, because there's a lot about carbon nanotubes that we don't know yet.
Despite anyone's predictions, we won't know what the material will be like until it's made. There's a LOT of other work that needs to be done on SE development regardless of what the material winds up being. And in the "worst" case, you can still build a space elevator on the moon with near-term materials.
One thing to remember is that, even if bulk CNT were limited to 30 GPa, we could still build the space elevator. It would just become limited by finances. That's because, with a density of 1300kg/m^3 and a strength of 30GPa, the mass of a seed ribbon (using the same assumptions as in my November article - safety factor of 2, and 1,000kg capacity) would be roughly 3,440 tonnes (i.e., 3.44*10^6 kg), or roughly 170 rocket launches (using current medium-lift rockets) to loft it (i.e., ~80 times as massive as in the 2002 NIAC report). The expense and logistics of creating a seed ribbon at that point (assuming you're launching from Earth) becomes much more daunting, but not impossible.
and for people raising other concerns, which I see in several places here:
Breaking is a minor issue. Most of it would fall up. The base station doesn't support the elevator, it holds it down. The Earth's rotation keeps it up. People tend to forget the scale we're dealing with here. The bits that fall down would burn up, land as ash.
Space debris is well mapped. We can avoid it, for the most part. Small adjustments made from either end of the elevator can be used to shift the bulk of the thing. Remember, serious plans for it call for building it on a floating platform, which can move, and rockets can be used to adjust the space end of things.
Storms, well, like I said, we can move the thing. Also bear in mind that storms only affect the part of it in the lower atmosphere. Resonance is an issue which is being seriously considered, as well as induced current.
Any more problems you'd like to raise? Read the wikipedia article.
Sheesh, what's wrong with these people?
If the current cable isn't strong enough, there are lots of possible solutions.
For example, the strength of the cable necessary is directly related to the mass of the earth.
One good sized metor at high enough velocity striking the earth, and we could build the elevator out of nylon rope.
Some other methods of reducing the mass of the earth are available here http://qntm.org/destroy
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And as we are not really able to produce material that would be strong enough and light enough to support the space lift even in perfect conditions (there are really nice Internet-available articles and research papeers on this issue), producing a practical model is still much more thing of fiction, than of science. Therefore any coating or protection from whatever may be hazardous for our lift needs also to be developed and is a topic for the future. But may be in far future...
Oh, and there was extensive research done on many different earth-to-orbit propulsion systems, some more possible than the others. My biggest enthusiasm got the nuclear-engine, but for obvious reasons research in this area is right now strongly inhibited (if there is any at all).
Imagine a spider on it's web; the web is torn at one point. The spider fixes it by producing more silk.
Imagine a small robot, even a nanobot, space elevator cable, made of many strands of carbon nanotubes. Imagine a way to pull carbon out of air and repair the cable.
A spider produces silk from the food and air it consumes; a nanobot could repair nanotubes in much the same way, by "breathing" carbon dioxide or pure carbon and doing repairs. Hell, it doesn't even need to MAKE carbon nanotubes, it could pick them up at "ground floor" and deliver them up the cable.
A self-repair system. No need to invoke convoluted biology and DNA.
You needn't go as far as free radicals, since Ozone by itself will react with the strained olefins in nanotubes, and is abundant in the upper atmosphere. Here is a computational paper on the matter, and here is an experimental follow-up. Then there's the problem of the increased UV radiation when you get higher, since your elevator is just one big chromophore.