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."

Damaged by Oxygen?

[Anonymous Coward]

What about using a thin layer of something (paint? plastic?) to protect against oxidation? Or would that add too much weight?

History repeating itself

[webmistressrachel]

As usual, with groundbreaking theories and inventions, we will deny it's possibility even after (if) we see it's work. But sooner or later, it may be viable, and soon acceptance and common use will follow.

Do I need to give any examples? Telescopes, electricity and magnetism, etc etc...

One way to find out

[spineboy]

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?

[irexe]

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?

Lunar Space Elevator

[randall_burns]

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.

How about Tethers and Rotovators instead?

[DumbSwede]

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).

Still feasible in other places.

[thisissilly]

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.

Re:Wireless Elevators

[PieSquared]

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 would have all the acceleration before it left the structure, probably killing everything alive on board. Coming back down isn't so bad as you have a terminal velocity, and acceleration is limited to gravity, only 1 G. The only way a ground based structure could do a "throw" would be if the "throw" were not strait up, but rather at an angle very shallow to the earth's surface, giving the acceleration on a track over miles. The problem with that of course is that the total air resistance while leaving earth is far greater, meaning even more, instead of less, energy. No, overall if you want a steady non-rocket based acceleration into space, the space elevator is *still* more viable.

Re:Is that the only problem?

[scdeimos]

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 will "fall up" even if the break is only six feet above the sea level. I'd hate to be on the station if that occurs - you'd get flung out into space beyond reach any sort of timely rescue.

Re:Impossible

[Anonymous Coward]

And even if we could somehow have mass production on such a large scale the failure rate of the tubes means there is a finite size for the computator mechanical mind before the probability of a tube blowing every minute rises to 1 and so they become unsuable. "everything that can be invented has been invented" - yeah right.

Re:Now Is Never

[Andrew Kismet]

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.

Re:Never?

[Baseclass]

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.

Fact is we're bound to unlock the secrets of the universe, knowledge is exponential.
Control of matter will be a no brainer. Dare I say even altering physics and our own realities.

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

[John Hasler]

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. 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.

Re:How about Tethers and Rotovators instead?

[Jeremi]

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).

Linking up with the end of a tether that is travelling in a circle at one to three kilometers a second sounds a lot like the sort of thing that the "Star Wars" missile defense program has been trying to do (i.e. "shoot a bullet with a bullet"). I expect it would be just as reliable too.

Re:History repeating itself

[Iron Sun]

As usual, with groundbreaking theories and inventions, we will deny it's possibility even after (if) we see it's work.

What an incredibly overbroad statement. Theories are only considered 'groundbreaking' in retrospect. Phrenology, the aether, phlogiston and Rutherford's model of the atom are examples of theories that had their moment in the sun and were found to be inadequate. You can't use the initial scepticism that inventions or theories that later proved to be correct faced in support of your desire to see this particular invention become possible, it's a spurious relationship. At least you phrased it in terms of if and may. If potential groundbreakingness and scepticism are a firm indicator as to validity, then I guess there's hope yet for the Keely Motor.

Re:Successful Test?!?

[kiwi77]

Just because we can make fibres with enough tensile strength to withstand loads for this thing doesn't address the entire construction question. My understanding is that we only have FIBRES. They have to be joined in a matrix of something, and that matrix will not have enough shear to support the tensile strength of the fibres. In carbon fibre materials, for example, an epoxy resin is cured around the carbon fibre. The fibres, because of their orientation and strength make a very strong structure; materials such as unidirectional CF can be used to strengthen the structure along load paths. But if the shear limits of the epoxy are exceeded, the thing will break. A great example of this is a Formula One chassis. Enormously strong becasue of their carbon fibre/epoxy structure, but when the break they shatter. So how will the fibres in the cable be formed into a structure? Seems to me the limit will be the glue, not the carbon.

Re:Never?

[Dyolf Knip]

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:The obvious answer

[randall_burns]

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.

The human genome analogy

[DrYak]

That's a very, very long time.

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.