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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."
What about using a thin layer of something (paint? plastic?) to protect against oxidation? Or would that add too much weight?
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.
Do I need to give any examples? Telescopes, electricity and magnetism, etc etc...
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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.
We consider ourselves masters of our universe, however there is so much yet to learn.
It always amazes me how a spider can weave a thread which is so strong and flexible yet for all our mastery of the earth we cannot yet reproduce its properties.
I believe we will find a pathway to the stars, whether it is a single tether or an entire webbed tower I don't know but I am not ready to give up on mans' inginuity.
liqbase
I thought the whole point was to be constantly rebuilding the 'string' (ie running repair bots up and down the structure or finding other repairing methods). This doesn't prove that space elevators are impossible. It just means we'd need to make a few more tech advances.
Which is, of course, always the case. But the starry-eyed folk have always known they'd have to engineer some constant repairing mechanism. I just don't see how this is a big deal.
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
Humans can't fly
Humans can't survive going more than 100 MPH
Can't transplant a heart
Maybe just a simple plastic coating will protect it. Saying something can't be done should mean nothing to most people.
..........FULL STOP.
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?
Even if it were possible to operate such a large collection of vacuum tubes with the small power supplies available for household electrical equipment, the glass fabrication process has too many flaws to enable mass production on such a scale. It would seem that the "personal computer" will never be anything other than what it is: a fiction.
I have discovered a truly remarkable
What puzzles me is why there hasn't been a bigger push for creation of a Lunar Space Elevator. A lunar space elevator could be built with existing materials--though the launch costs would be significant. We'd learn a lot from this kind of practical project--and raw getting materials into orbit for a variety of purposes would get much less expensive.
Why this obsession with a full blown "Space Elevator" when there is so much that can be done in the interim with tethers? Rotavators would require significantly less demanding materials and only require getting above atmosphere like SpaceShip One did recently. Then clamp on and ride the rest of the way to full orbital velocity (the tip would appear to hover briefly in sync with the Earth's rotation just above the atmosphere).
Letter To Iran
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.
For Earth, perhaps. But for Mars and Luna, space elevators could still be built. In fact, a Lunar elevator could be built out of Kevlar, without the need for carbon nanotubes.
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
-- Should you believe authority without question?
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What you propose is essentially what's being done. A small amount of money is being placed into theoretical research on Space Elevators, and that is what gets into the news because they are fun to think about, but the vast bulk of the money is (quite rightly) being spent on basic carbon nanotube materials research -- which is a good investment whether we end up building space elevators, or not.
As it is we're just pouring money into a money pit of a dream impossible with today's technology. Typical of our government... missle defense anyone?
Can you point to any actual figures about how much money is being wasted on research that has no application outside of Space Elevators? Or are you just assuming the worst, and bellyaching about the products of your imagination?
I don't care if it's 90,000 hectares. That lake was not my doing.
When we better understand genetics and what it takes to build self-sustaining repair subsystems, we will be able to build sustainable structures that exist in our atmosphere and beyond it. It's the same with our space stations and our space vehicles. They have an expiration date that is inevitable based on chance encounter with destructive environmental agents. The Earth is a self repairing structure that has been alive for billions of years. The Moon has been up there quite a while, too, and it's connected to the Earth by gravity. If we find a way to ride that link, we may well have the elevator we need already there.
But as far as coping with environmental damage, we have the same issues on earth with just about every object we create. It wears out and it wears out pretty rapidly. Even we wear out, though our repair systems allow us to do quite a few amazing things over a long period of time before we die. If we really want renewable structures, then they will have to have a "nervous system" of sorts that perceives structural damage and a "repair system" of sorts that can restore damaged areas to original state.
This is not impossible. Our bodies are proof that it is possible. We just don't know how to do it yet. Likely because it's never been a big enough priority. When we start to use up all the easily accessible non-renewable material resources on the planet, we may start making breakthroughs in this area of recycling and repairing rather than discarding (a la "cars no longer go to the junkyard because it's too costly to waste all those materials, so instead we build cars that can repair themselves and last 3 times longer (at which point we'll probably call them "horses").
Never isn't quite now, but it's not far.
Are they seriously suggesting there is no way to make a space elevator or just not this way? I would think you get work out most of these kinds of issues by engineering better materials and by using something more redundant. If one cable isn't strong enough in the face of defects could they use say four that would each support the corner of an elevator? Could they make cables that would diagnose their own injuries and repair themselves? Every weakness is something that can be addressed and fixed.
At what price learning? At what cost wisdom? The price is a man's peace of mind, and the cost is his life.
... of the theoretical maximum strength of a material.
:)
Nearly perfect crystals (what TFA is whining about) have been known to fail catastrophically, and quickly for as long as people have associated the word 'brittle' with 'crystal'.
Now, many *amorpheous* covalent structures (eg: window glass - although it is often weak) can have both extreme strength - as strong as a perfect crystal, perfectly aligned - and extreme thoughness (robustness in the face of damage).
Extremely complicated - although not amorpheous, materials can also be as strong as their constituent carbon bonds, and can (not usually at the same time in nature though) be even more forgiving of damage. Most woods (particularly the softwoods we are surounded by) for example, will react to penetrations (like nails) by bending around the damage, and with the massive crosslinking, the column of fibres damaged is only weakened for a short distance near the damage.
This means that we only can be sure that the *largest* hole in the material will cause significant weakening as the others should not be right next to it and thus would be 'second and subsequent' links in an analagous chain, and thus of much lesser consequence. Amusingly, a hole wouldn't neccessarily even cause weakening proportionally to its fraction of the cross-sectional area of the material.
TFAuthor noticed that a single carbon tube is weakened after losing a Carbon, way weakened by two, and toast shortly after... then used his own 'secret recipe math' to 'prove' that big piles of nanotubes would be statistically likely to fail.
Without defining the *exact* nature of the cross-linking reinforcing the tubes you can make almost no statements about how forgiving the material is going to be of damage. The researchers quoted in TFA who are working with actual buckytubes, trying to actually build something, are correct to shrug off the TFA as being both theoretical, and wrong. They have more pressing problems (like getting past the 1 GPa point) than worrying about the theoretical maximal properties of layouts of tubes that they were not even *considered* using.
And, yes, it is freaking idiotic to say something technological is impossible, when the physics do not rule it out. It is merely *daft* to assume that something prohibited by current physics is impossible - but that is not the case here.
This isn't science, it's an ill-conceived editorial. Ignore this article and get back to work, my space monkey minions! Soon space will be ours!
Liberty you never use is liberty you lose.
Yes, lightning is a definite hazard for a space elevator.
The solution: locate the space elevator in a lightning-free area.
I don't care if it's 90,000 hectares. That lake was not my doing.
Try this thought experiment. Assume a material that can support 2 feet of itself (wet spaghetti, perhaps). Make a two-fiber bundle 1 foot long. You now have a 1 foot cable capable of supporting the weight a 2 feet of fiber. Attach a single fiber 1 foot long to it. You now have a 2 foot cable capable of supporting the weight of 1 foot of fiber. Bundle two of these cables together. You now have a 2 foot cable capable of supporting 2 feet of fiber. Attach a foot of fiber. You now have a 3 foot cable capable of supporting 1 foot of fiber. Bundle two of these together and attach a foot of fiber. You now have a 4 foot cable capable of supporting a foot of fiber. Repeat until you reach the sky[2].
[1] Well, perhaps not any length. Eventually self-gravitation will cause your cable to collapse into a doughball.
[2] For a real skyhook the taper need not be this extreme as this for obvious reasons.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
Hey, some cat just showed up in my living room. What gives?
barack to the future?
... that treats today's limitations as if they extend into the future indefinitely.
So far as I can see, all the objections mean is that a space elevator cannot be built with the technologies we currently have -- and all of them seem to be of an engineering bent, as opposed to some fundamental theoretical problem. Engineering problems tend to get solved over the long haul.
And even if the problems presented do turn out to be too difficult to construct an Earth-based space elevator, the technology could still be used on the Moon, which presents a much smaller challenge. I suspect that we already have the capabilities required to construct a lunar space elevator -- all that we lack is a permanent lunar base.
Of course, the only reason anyone would built such a bridge is as a prototype demonstration to scare up investors. The potential ROI for a space elevator is pretty spectacular, not so much for a bridge... and buckytube isn't cheap.
//Information does not want to be free; it wants to breed.
Dammit! There goes my dream of hopping on the space elevator and punching the button for every floor ...
"My God...it's full of trolls!"
Civil engineers simply build things stronger than they need to be. The safety margin allows a structure to absorb some damage from rust, rot, barges running into it and so on while remaining robust enough not to kill anyone.
Set up an elevator, and when micrometeorite damage reduces the safety margin too much, use it to haul up its replacement.
Here's the thing, creating significant orbital infrastructure would be greatly faciliated by a source of raw materials, oxygen, iron and others needed. The moon might not have everything you'd need-but it would have quite a bit. There is _serious_ value in having cheap materials orbit. If nothing else, folks could build shielding for satellites-but I expect the market would evolve rapidly here. What would it be worth to get oxygen from moon rocks instead hauling it to orbit(say for the international space station or other ventures)? A great deal I expect.
It is theoretically far cheaper to move things from the moon to earth orbit than from the earths surface to that same orbit. The main problem is this kind of infrastructure doesnt exist.
So, we've found a few flaws in our plan. I doubt that means that this will be scrapped forever. We're always developing new materials and new ways to apply them. Perhaps someone will come up with a nanotube which has a non-reactive sheathing that can resist oxygen erosion.
There are also other avenues to space. We haven't heard much about laser powered propulsion, but there are possibilities as civilian and military researchers develop new and more powerful lasers. It would be a nice swords-into-plowshares project if we could use some of the military's new weapons for an application like this.
Also, we don't necessarily need to be able to loft huge payloads at first. If we can send up small satellites or maybe even a small manned capsule repeatably and cheaply, it would be a good start. That is after all how we started with chemical rockets, so there's nothing wrong with starting small.
It's good to use your head, but not as a battering ram.
You're right, I think.
It's like saying that the Human Genome will never be decoded in less than 50 to 75 years.
That was probably true when the HuGo project started, given technologies available back then.
But because the biggest effort was done by public Universities, freely sharing result, tremendous advances were made, and with it incredible advance in sequencing technology.
In the end most of the work was done in 15 years, the last tiny bit being finished after 20 years.
According TFA, the main problem is that there's a gap between the theoretic maximal strains that can be sustained by a "perfect" strand of nanotube (~ 50% more than needed) and the strains that can be sustained by a ribbon produced with technology we could have in a near future ( 1/10th of what is needed).
Thus the discrepencies between the NASA experts (nanotube can make elevator possible) and TFA's autor (we cannot make perfect enough nanotube-based ribbons for a space elevator)
I think if the space elevator research is done by networks of openly colaborating universities "à la HuGo project", maybe advance in nanotube technology will be made faster. More money will be brought by investors in related industries (like how faster and newer sequencer were made during HuGo), and maybe will be able to develop "good enough for elevator" technologies in the near future, sooner than the pessimistic article.
"Sufficiently advanced satire is indistinguishable from reality." - [Tips: 1DrYakQDKCQ6y52z6QbnkxHXAocMZJE61o ]
I will grant you that things of this scale do not fit the paradigm of everyday items (aka "everyone owns a washing machine"). But to dismiss some of these items is just asking for trouble.
Compute the resonance frequency of a device 60,000 miles long.
Which mode would you like to excite? Things don't always fail at the first resonant frequency. Many/most do, which makes the others that much more spectacular (and unexpected, I might add).
What danger to airplanes? Are you envisioning something that's going to randomly and rapidly maraud across the surface of the Earth or something?
Of course not. Not until it snaps due to a flaw or an unforseen event. I'm not saying that there will be a plane flying around when the string goes pop (note, I said "when" not "if"). That chance is very, very remote - you know, like large-comet-impacting-Jupiter remote.
On the flip side of that argument, luckily, nobody has any reason to intentionally try and fly an airplane into such a structure. That's why planes never fly into buildi... oh, right.
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.
So what happens when the fiber is severed in low earth orbit? There's a lot of money tied up in communications satellites, and the companies who own them would be pretty pissed off to lose them. Not to mention the public outcry if the loss of a major bird or two interupts their viewing of the World Series.
Even more interesting is what you're going to do with all the low earth orbit satellites. There are lots of them out there, and they'll be travelling at up to 7km/s relative the fiber (perpendicular to the strand axis, esp. for polar orbits). Not all of them are active (LAGEOS and similar passive reflectors come to mind), and will no be able to correct their orbits. No matter how thin the strand, eventually their paths will cross.
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.)
Yes, when you deal with orbital dynamics, the x, y, and z we deal with on the ground doesn't apply anymore. In addition to the article, there is one other thing that will keep the space elevator from happening in the lifetime of my children: safety. I've mentioned it above, but this sort of thing is going to have to be safe. No, I take that back, it's going to have to have a proven failure rate of zero. Too many things can go wrong, and the publics tolerance for failure is so thin - well, it makes a carbon nanotube thickness seem large. I think the political hurdles are larger than the technological ones - and that's saying quite a lot.
Is it just my observation, or are there way too many stupid people in the world?
This article from doing actual measurements found a highest strength of 63 GPa:
P DFs/science-9.pdf
n s/16.MSE%20A334demczyk.pdf
1 /5502/283
Strength and Breaking Mechanism of Multiwalled Carbon Nanotubes Under Tensile Load.
SCIENCE, VOL 287, p. 637-640, 28 JANUARY 2000
http://bucky-central.mech.northwestern.edu/Ruoffs
This report showed actual measured tensile strengths up to 150 GPa:
Direct mechanical measurement of the tensile strength and elastic modulus of multiwalled carbon nanotubes.
B.G. Demczyk et al.
Materials Science and Engineering A334 (2002), 174, 173-178.
http://www.glue.umd.edu/~cumings/PDF%20Publicatio
Both of these studies were done on multiwalled tubes since they are larger and it's easier to make attachments with them.
In the earlier study in Science, the authors from SEM imaging noted that it was actually the outer single-walled nanotube that broke first therefore it was carrying the load. This would make sense from the way the attachments were formed which could only form a bond with the outer surface of the multiwalled tube. Therefore the numbers quoted were for the strength of this outer single-walled nanotube using as thickness only that of this single-walled nanotube.
However, in the later study in Materials Science and Engineering, the authors believed the attachments were made to all the layers of the multi-layered nanotube, which would explain their higher measured strength.
The prevailing theory is that the range of strengths is due to the number of imperfections in the nanotubes. So we should be able to look at the nanotubes at the nanoscale using SEM,'s, STM's or AFM's and find which ones have the least imperfections. These should be the strongest tubes.
In the Science study, 1 out of 21 of them, 5%, have the best strength, 63 GPa. At a production of millions of tubes at a time this should still be feasible economically and technically.
The lengths of the nanotubes in these studies were however, were at the micron scale though. Nanotubes have been created at the centimeter length scale, but as far as I know the strength of these have not been tested.
Note that the reported strengths of centimeter long or longer "fibers" made of nanotubes being less than 1 GPA are not measuring the strength of individual nanotubes at these lengths. This is because the fibers are composed of the nanotubes stuck together end to end by weaker Van der Waals forces, rather than the much stronger carbon-carbon bonds that prevail in individual nanotubes.
Here is one study that detects, characterizes defects in the nanotubes at the nanoscale:
Resonant Electron Scattering by Defects in Single-Walled Carbon Nanotubes.
Science 12 January 2001, Vol. 291. no. 5502, pp. 283 - 285.
http://www.sciencemag.org/cgi/content/abstract/29
Methods such as this might make it possible to find the nanotubes with the least defects beforehand and therefore automatically select those of the highest strengths.
Bob Clark