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."

Never?

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.)

Re:Never?

There is plenty we don't know and many breakthroughs left in the universe, but I think it's human arrogance to think we're capable of omnipotence.

Sure, carbon nanotubes are neat, and gave us the impression we could build stronger structures and materials than previously. But why does their existance mean we're sure to find something equally strong AND able to withstand being a space elevator cable?

Don't get me wrong - saying 'never' is unwise, but it's almost as bad to assume humanity will be capable of everything one day.

Re:Never?

Personally I'm of the opinion that we can eventually master all aspects of the universe.
Sure it may take 1,000's, 1,000,000's, or perhaps even 1,000,000,000's of years.

And I'm of the opinion that unless there's some mass societal changes, no one's going to be doing serious science in 100s of years.

Re:Never?

When we are talking timelines of 1,000 or 1,000,000 years, any kind of "blip" that happens in human advancement will be short term. Serious science is perpetual. It's part of human nature. You don't need 100% of the people advancing science - you never had that. It's more like 0.0001% of the people.

Re:Never?

Eh, you're both right. Either we become extinct on this one lousy rock in the next century or two, or we expand out into space and basically become unkillable. After that all we need is time.

One line from Vernor Vinge's _A Deepness in the Sky_ that caught my attention was the almost casual mention that when the human race had expanded to a volume many hundreds of light years wide, "Earth had had to be recolonized from scratch 4 times" since the civilizations would last for a few thousand years and then self-destruct to totality.

Which is what really pisses me off about NASA. All we need for them to do, all we've _ever_ needed from them, was cheap and reliable access to LEO. Probes, stations, zero-g experiments, even the moon missions, it's all really super cool but we've got universities and companies and throngs of avid would-be astronauts who would do it if they only could afford to.

Re:Never?

An infinite universe is no guarantee that everything will happen. There are many infinities. For example, there are an infinite number of numbers between three and four, but none of them are five.

Crap

For example, there are an infinite number of numbers between three and four, but none of them are five.

Crap. You just made my cat disappear. Thanks alot.

Re:Never?

. . .there are an infinite number of numbers between three and four, but none of them are five.

"You fool," said the mathematician. "Don't you know that if you can only move toward the girl half the distance each time you'll never reach her?"

"Yes," replied the engineer. "But after awhile I'll get close enough."

KFG

Re:Never?

> I guess the set of possible relative positionning of particules(or basic elements) in the universe is infinite uncountable.

Not necessarily - Planck length [wikipedia.org] may be a minimum [blogspot.com] unit of distance in the universe, making the set of possible states potentially not merely countable but (along with the other Planck units) finite.

Re:Never?

A minimum unit of distance, and a finite number of states for a minimum particle to exist in, would indeed mean that there's a finite number of states for an area of any particular size, but if the universe has no bounds, it is still not finite.

Re:Never?

Rational and real, since all rational numbers are real numbers.

Let x be a real number, such that 4 > x > 3.
Let y be a real number such that y = ((4 - x) / 2) + x

By basic algebra, ((4 - x) / 2) + x x
and y != x
By our definition, x > 3, and transiti

Re:Never?

Here's a simpler, more general way to state it:
For every two real numbers A, B where A < B, there exists a number x = (A+B)/2.
Since A < x < B, you can repeat the existence postulate for A, x and x, B
This is true for A,B = 3,4.

Re:Never?

I'm sorry, but what? In what geometries (where betweenness has an actual significance) which contain the integers in their natural ordering have five between three and four? I have studied quite a lot of math, including at the graduate level, and I have come across nothing that leads me to believe that your comment is any more that pseudo-intellectual gibberish intended to sound insightful but which is actually devoid of any real meaning. What vies on infinity could impact the discussion at all? Do you mean that if we view the number line as a giant circle which loops back upon itself that five is between four and three? If this is the case, I contend that betweenness is meaningless, as any number is then "between" any other two numbers.

There is a time and a place for mathematics to be deep and mysterious. If you throw around comments like this, nobody will care when we reach one of those times.

Of course, if this was just an attempt at humor, forgive me. My anger should be directed at the moderators!

Re:Now Is Never

what a meaningless (parent) post.

Bridging the gap between computer science, robotics, molecular genetics, and biochemistry seems like a bizarre and convoluted route to addressing the problems stated in the article.

First, modeling engineered devices on real world objects, even features of living objects, is not a new concept. Second, we're talking a fairly simple system, a big long ribbon, not a complicated self-regulating autonomous device. Nor is there any reason to make something that would need to be as fault tolerant and robust as possible more complex than it needs to be. So, self-reparing system may sound sexy, but if a simpler mechanism can be devised than inventing an entirely new class of devices and methodologies to fix the problem, that is rightly the domain of material sciences, i fail to see why we'd want to start spouting off ungrounded hype about inter-disciplinary science that at the moment is... to be kind, speculative.

Re:Now Is Never

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.

Wireless Elevators

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.

Re:Wireless Elevators

That's called a rocket.

Re:Wireless Elevators

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.

The acceleration would kill you. That's the nice thing about the elevator, it could be a very mild ride.

Re:Wireless Elevators

True, but both the space elevator approach and the approach of an almost immediate impulse launch (versus a conventional rocket) would be that we don't have to lift the fuel. The elevator has the added benefit of a possible counter-balance, but the main point is still that all current rockets use lots of fuel to lift other fuel.

This would naturally also make any kind of "power beaming" technology interesting, even if it would be quite inefficient, as long as it could be transformed into significant thrust easily in the receiver.

Re:Wireless Elevators

There is a slight difference with that: the acceleration takes place over the entire flight to orbit, not entirely on the ground. Instead of having a steady acceleration of at most a few G's, a station based on the ground "throwing" an object strait up wo

Successful Test?!?

> 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.

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.

Re:Successful Test?!?

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 b

Never say never

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.

Re:Never say never

Spider silk has been synthesised, and there are genetically modified goats that secret spider silk proteins in their milk. Strength to weight wise, spider silk is comparable to Kevlar.
http://www.isracast.com/tech_news/271204_tech.htm [isracast.com]

Steve

Psha!

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.

unwarrented negativism

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.

Re:unwarrented negativism

Is a space elevator impossible, just because this one method might be impractical?

I think the point of the article was that someone woke up and saw that it really is a hard problem that will take a vast amount of resources - and not the simple ribbon you drop from the sky than people outside of the physical sciences and engineering are thinking about. It's a very long way up - and then to keep it up the you need a counterweight and station keeping systems - plus the obvious of having a highly conductive material with an incredible potential difference from one end to the other (magnetic feild etc) if you are talking about carbon nanotubes. To get an idea of the scale of things of this elevator, consider building a railgun out of carbon nanotubes designed to accelerate something the size of the capsule that will be going up. Wrap it around the equator twice. Now stand it on it's end with some sort of living platform in the middle of it. That's your free standing beanstalk in the simplest form. Microwave or laser powered climbing robots may sound cool, but it's a nasty and expensive hack to keep the heavy stuff on the ground and rather bizzare when you have a very highly conductive material that can get power to motors a lot more easily than an incredibly lossy broadcast power system.

The next thing is to stand your beanstalk up you need to do something like ship it to geostationary orbit with a rocket and unwrap it - so we are talking about sending a vast amount of mass up there by rocket. Obviously from this a beanstalk would only make sense in the context of it being a small piece of a larger plan that involves getting incredible amounts of mass into orbit. There's been space snakeoil companies around before (eg. the Australian spaceport company which consisted of two people - I'm assuming one to scam the money and one to answer the phone) and unbelievably optimistic beanstalk people asking for money may well exactly that, since with current designs it would have to be built of unobtainium and requires robots powered by a technology Tesla abandoned a century ago once previously unknown laws of physics became clear.

One way to find out

Just do it - or at least a small model. After all these critics are in the same family that once said

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.

Is that the only problem?

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?

Re:Is that the only problem?

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?

The considerations you listed aren't considered problems because there are fai

Re:Is that the only problem?

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.)

Re:Is that the only problem?

if it breaks, points above the halfway mark fall fall upwards.

That's not actually correct. The entire ribbon is under tension due to the centrifugal force imparted on it by the counterweight (the station in space), so all of the ribbon above the break w

Impossible

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.

Lunar Space Elevator

What puzzles me is why there hasn't been a bigger push for creation of a Lunar Space Elevator [wikipedia.org]. 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.

Re:Lunar Space Elevator

Because it costs a lot to go to the moon? Did you think through your question? At all?

How about Tethers and Rotovators instead?

Why this obsession with a full blown "Space Elevator" when there is so much that can be done in the interim with tethers? Rotavators [wikipedia.org] 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).

Re:How about Tethers and Rotovators instead?

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 wi

Liftport already responded to this

This has already been addressed by Liftport, [liftport.com] 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 [wikipedia.org].

Still feasible in other places.

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.

No imagination.

Pugno, however, argues that inevitable defects in the nanotubes mean that such a cable simply wouldn't be strong enough.

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 [qntm.org]

-- Should you believe authority without question?

Re:No imagination.

ObTrek [memory-alpha.org]:

"Easy: Change the gravitational constant of the universe."

"What?"

"Change the gravitational constant of the universe, thereby altering the asteroid's orbit."

"How do you do that?"

"You just DO it, that's all. GAHH! Where is that doctor?"

"What Geordi is

Low-earth orbit -- monkey physics fails again.

Payloads, or tourists, would simply ascend the cable into low-Earth orbit, eliminating the need for rocket launches.

Well there's your problem right there -- you can't take a space elevator to low earth orbit. A space elevator that puts you in low earth orbit is moving at an angular velocity 18 times faster than the earth, and is therefore quickly destroyed.

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!

It's a foolish person ...

... 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.

Re:Damaged by Oxygen?

They're too slippery to bond that kind of thing effectively:

http://www.sciencedaily.com/releases/2005/11/05111 7114309.htm [sciencedaily.com]

Another way?

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 enoug

Re:Damaged by Oxygen?

If I understood correctly ("oxygen atoms") the author was not refering to O2 nor O3 but simple free oxygen radicals. At high altitudes (ozone layer height and above) the UV radiation is strong enough to split O2 and O3 molecules into free radicals (homolytic cleavage). The product is represented in chemistry as O. (O with a dot). This is a relatively stable molecule, but very reactive. And I mean very. It will do anything to bind to something and get back to favourite 8 electrons in valence shell configuration.

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).

Re:Damaged by Oxygen?

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 [acs.org] is a computational paper on the matter, and here [acs.org] 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.

Re:At Last

Then we could turn to the space elevator problem, presumably with some defect-free growth process already in hand.

What you propose is essentially what's being done. A small amount of money is being placed into theoretical research on Space Elevators, and

Re:Oxygen!! What about lightning!?

If they're worried about corrosion, what about a nice dose of lightning?

Yes, lightning is a definite hazard for a space elevator.

The solution [www.isr.us]: locate the space elevator in a lightning-free area.

Re:Bah. You could make it out of steel cable.

I certainly couldn't disprove it, but I'd be surprised to find that steel would actually work.

It would work. You can construct a cable of any length[1] of any material that can support its own weight over a finite length.

Try this thought experiment