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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."
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.
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).
The space elevator falls into the "Really Big" category of things, and using your traditional, every-day intuition about how things behave is actively unhelpful.
We are talking a device ~60,000 miles long, feet wide, and paper-thin. So...
I am thinking of storm type winds blowing it off balance
The atmosphere extends up a few tens of miles at most. The Space Elevator is 60,000 miles long.
making it resonate
Compute the resonance frequency of a device 60,000 miles long.
Even to the extent it's a problem, it's not like it's hard to react to; you've got all day.
the danger to aeroplanes,
What danger to airplanes? Are you envisioning something that's going to randomly and rapidly maraud across the surface of the Earth or something?
It's way, way, way easier to dodge a stationary space elevator than all the other constantly moving planes in the sky.
the disastrous consequences of breakage
You're just assuming. Somebody beat me to pointing out this is false, but I want to point out you're assuming based on your everyday experience. It works poorly in this domain.
For instance, what you probably think happens if there is a cut near the ground is the exact opposite of what happens, because your intuition is not set up for these kinds of problems.
You need to turn to the math on this. Other people have worked out the issues. Most of what you consider the "real problems" aren't, and I don't mean that as a comment on your particular post, I mean it in general. Other things that you might never think about are, such as the concern raised in TFA, which I think are valid but aren't necessarily stoppers, and the ever-present question of whether we'll ever be able to turn out 60,000 miles of cable of any kind.
Your intuition is worthless. Nothing personal; mine is too. Having studied the topics involved I can say I understand some of this stuff intellectually, but I can't say I understand it in my gut. But I do know not to trust my gut in this domain.
(For what it's worth, similar concerns apply w.r.t. nanotechnology. Your intuition about how things work does not do very well at that scale. Our brains function at the in-between scale we all live and work in, and does not do well outside of that domain.)
(60,000 mile note: I'm assuming the elevator design that extends in both directions from geosync, as I like the "throwing" ability it exhibits over the counter-weight-just-outside-of-geosync model. Other distances are possible but don't fundamentally change the results.)
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.