Are space elevators hype?

[NoXion]

This is the first time I've come across this, but maybe I haven't been paying attention. Apparently space elevators are "a million times more unfeasible than Mars One", at least according to someone on a forum I frequent. I'm not asking for help in a debate, but rather I'm hoping that someone here will be able to confirm what they're saying.

Here's what they said:

It's amazing that until now, voices of reason have been insulted, slammed, and silenced in the mainstream, and even in scientific publications.

Even more amazing is that voices of reason continue to be universally slammed on the topic of space elevators, an idea that's easily a million times more unfeasible than Mars One.

What's wrong with space elevators? True, we don't yet have a cable strong enough for them, but that kind of thing hardly out of the reach of potential advances in materials science.

A society that is technologically advanced enough to build a space elevator doesn't need a space elevator. The problems that the elevator would alleviate, heavy-lifting, would have needed to be dealt with in order to build it.

I think that misapprehends what makes space elevators useful. It's not about heavy lifting per se - any fission-powered rocket will do that - but rather it's about efficiency. A fleet of rockets will consume fuel/propellant with every trip, whereas a space elevator only has to be built once and can then exchange energy between stuff going up and stuff going down with minimal losses.

It's like saying that railroads are useless because we have motor vehicles, when in fact both have their own sets of advantages and disadvantages making them useful in different situations. Heavy lift launch vehicles are good for when you need something quickly lifted into orbit, like transferring passengers from a spaceport on a planetary surface to a space station in orbit. Space elevators would be useful for providing a steady stream of materials to and from space in an efficient if not fast manner.

Strength isn't enough. Not only must the cable must be made of a material stronger than we've ever discovered, it must also be lighter than any material ever discovered (including gases), more rigid than any material ever discovered, and harder than any material than ever discovered. And even then, it has to break the previous record for these qualities by many orders of magnitude to even be considered suitable. And even then, there has to be a way to mass-produce this miracle fantasy material in a way that no material has ever been mass-produced before. And even then, there's no known way to actually get the elevator up there than to break it into millions of pieces and spend trillions of dollars and millions of tons of rocket fuel with thousands of missions into space to deliver the payload and weld each piece to the next one at a time. Wasn't the whole point of the space elevator to avoid wasting fuel on trips to space?

... if all those things were true, it would be such a world-changing miracle that the last thing on anyone's mind would be to build a rope to climb nowhere. It would literally make more sense to try to use the material to make a floating railway across the pacific ocean.


But your question really exemplifies what I'm saying. You've been reading articles that cast the idea in a non-skeptical light. This is what mainstream journalism does on topics it can't comprehend such as space travel.

So, what's the skinny on this? Are space elevators really as unfeasible as this guy says they are?

[Eternal_Freedom]

I did an entire dissertation on this. My conclusion was, yep, they're not a viable concept. They offer a cheap, easy, reliable and say way to get into space, but to build one you need a cheap, easy, reliable and safe way to get into space.

Cable strength isn't the only massive problem. you have to build a space station up at geostationery orbit level, you have to have a counterweight further out (one estimate I cited said the cable would have to be 144,000 km long, much longer than the 36,000 km geostationery altitude).

Plus the fact that any satellite orbiting below GSO will eventually hit the cable, so you have to plan for that. The cable needs to be anchored on the equator, which basically means the middle of Africa or the Amazon river delta. THere are so many other problems I can't add them in quickly.

[The Duchess of Zeon]

I disagree. The location of the elevator would be in mountainous Ecuador, where it would be directly anchored to a mountain, or better yet on the central spine of Halmahera island in Indonesia. The initial strand would be launched by an Orion, and we would accept atmospheric pollution from it to do so, but once the initial strand is established, we'll use the elevator to build itself the rest of the way, exactly the same way that you build up the cables of a suspension bridge. The critical thing is that performance could be matched by Orions, but we don't want to use more than we have to to build the elevator for environmental reasons. So the elevator is the greentech solution after a highly polluting initial phase, which is minimized by incorporating engineering practices from bridge construction. It is nothing more than a bridge into space, after all, because the outer part of the elevator forms a stable counterbalance so that it's effectively anchored at both ends. The satellite issue can be fixed by modern satellites with ion propulsion and autonomous programming which can alter their orbits to never interpose with the cable. If we're going to have robotic cars, this will be almost trivial by comparison. With our continued advances in carbon fibre technology, the space elevator will be possible in 100 - 200 years, and will be built soon after, by the Chinese if not us.

[Eternal_Freedom]

The point about using Orions as a way to get the material into orbit is a good one. I hadn't considered it, since my dissertation was one whether or not space elevators are viable in the next two or three decades. And your solution does require actually building an Orion launcher, which is a whole can of worms on it's own.

[sarevok2]

How is the space elevator going to deal with atmosphere effects pushing it ?

[andrewgpaul]

Is that even something that would be noticeable? >99% of the length of the thing is going to be outside the atmosphere.

[The Duchess of Zeon]

How is the space elevator going to deal with atmosphere effects pushing it ?

As an expert in Vortex-Induced Vibration, I can say that the size of the cable relative to atmospheric density and the length of the cable relative to the atmospheric thickness will dampen the main atmospheric driving effects of any instability and that a variety of passive and active stabilization measures could be adopted if I'm wrong, all of which would require a great deal of explanation but suffice to say, air is of very low density and the kinds of things we see in drilling risers and mooring cables in the ocean won't be replicated in the atmosphere despite much greater flow velocities, in fact, problems only occur when the frequency of oscillation and natural frequency of the structure are very similar, and definitely high reynolds number turbulent conditions preclude this harmonic from developing.

[Simon_Jester]

I am unsure whether an Orion drive is required as opposed to, say, a series of extremely large heavy-lift rocket launches.

The biggest obstacle is getting the cable material- carbon nanotubes have the requisite theoretical strength, but as yet it is not certain they can be made to the quality required.

The second-biggest obstacle is, if an Orion drive is required, actually making an Orion drive work. This problem is understood in theory but in practice is a really big engineering problem. Nothing ever built would be like it.
________________

More generally... we can say today that a space elevator is "possible" in the sense that someone in 1800 could say that the Golden Gate Bridge was "possible." They knew suspension bridges existed and could be built. They could reasonably theorize that cables of steel could be made to carry the weight of such a huge bridge. They could assert that the problems of digging out and laying foundations for the massive bridge towers could be solved, that a century or two of advance in steel production would allow strong enough materials to be produced on a large enough scale.

But realistically, the obstacles involved were so great that no one could explain in detail how such a thing would be done.

If our technological capabilities continue to grow as they did from 1800 to today, it is almost inevitable that space elevators will be a do-able thing some time in the 21st or 22nd century. They represent a reasonable extrapolation from present technology... but not one we are yet prepared to design in detail.

[madd0ct0r]

build it in space from asteroid material, lower it down?
a few decades longer to do then orion, but less bad.

[The Duchess of Zeon]

build it in space from asteroid material, lower it down?
a few decades longer to do then orion, but less bad.

That would also work, yes.

[Eternal_Freedom]

I'm not sure that would actually be any easier; you'd have to lift the manufacturing facilities for the cable into space, and they'd need to be large-scale facilities to build enough cable material in anything like a reasonable time.

[Simon_Jester]

Yes, but you can put them into space a few hundred tons at a time in modular packets, which means you can get away with just launching a string of Energia-sized rockets.

Or Sea Dragon if you're ambitious.

By contrast, a rope long enough to reach clear to geosynchronous orbit is going to weigh thousands or tens of thousands of tons no matter how strong and light the materials are.

[Irbis]

*sigh*

Didn't we already have that discussion? Several times? While yes, most conventional designs of Space Elevator do require very strong cable, there are other designs perfectly viable today, not dependent on any future materials, ones trading requirements of conventional elevator for either energy or land usage:

http://en.wikipedia.org/wiki/Space_fountain
http://en.wikipedia.org/wiki/Launch_loop

Both links have references to work done by actual engineers and after looking at these papers I didn't see any reason why either wouldn't work, for less than future rocket programs are projected to cost, actually.

Anyway, OP, your guy is spewing nonsense. There are so many things wrong with that quote listing all of them would take too long, but you can simply ask if he is familiar with such basic concept as centrifugal force (that would take care of cable's weight, never mind the fact 90% of the cable will be outside of measurable gravity), the amounts of materials produced yearly today, or strength of materials we already have in the labs. Literally nothing what he wrote was true, and almost all of it can be also applied to undersea cables - ask him if he is aware how old and big these are and just how many we have around today. Impossible quantities? Pfft

[Irbis]

Oh, and one more thing:

By contrast, a rope long enough to reach clear to geosynchronous orbit is going to weigh thousands or tens of thousands of tons no matter how strong and light the materials are.

Well, yes. But the thing is, you don't need it to build the elevator. The guy from OP is using favourite trick of the creationists: "how random storm in the warehouse can assemble Boeing 747 with all parts in right place? Checkmate, atheists!".

Most of sensible elevator designs I saw propose lifting only tiny weak cable at first... Then use it to slowly pull enough material up to double the cable thickness. Repeat until you double it enough times to get desired structure.

When you build rope bridge, you start with throwing starter rope over the chasm at first, to pull more solid ropes until you have solid foundations upon which you can mount planking. You do not throw foundation ropes, walking boards and supporting lines all at once. Only total idiot can propose that.

[Sky Captain]

I think big problem would be space debris. Active satellites can maneuver to avoid cable, but random space junk can't and given that the cable would cross all used Earth orbits there would be lot of junk with potential to hit and break cable. So to make space elevator feasible you would need to clear all near Earth space. maybe fitting cable with some kind of thrusters to swing portion of cable out of path of incoming junk could also work

[Irbis]

I think big problem would be space debris. Active satellites can maneuver to avoid cable, but random space junk can't and given that the cable would cross all used Earth orbits there would be lot of junk with potential to hit and break cable. So to make space elevator feasible you would need to clear all near Earth space. maybe fitting cable with some kind of thrusters to swing portion of cable out of path of incoming junk could also work

NASA actually did feasibility study of this:

http://www.niac.usra.edu/studies/521Edwards.html

Conclusion: ribbon would be strong enough to effortlessly withstand hits from small objects, large objects big enough to damage it could be detected days or weeks in advance, then deflected, by say laser ablation. Even large events with bigger chance of damaging ribbon, like meteor showers, can be counteracted to a degree. Simplest method would be rotating ribbon edge-wise toward threat, reducing impact risk to astronomically low values.

I am not saying there is absolutely no risk, but damage and wear on high load infrastructure is topic actively researched how decades now and a lot would apply to elevator, too. Especially seeing that even debris that would manage to cut it wouldn't have enough energy to significantly move it so there would be time to send a team from top station to quickly secure place where it was damaged until it could be repaired.

[Guardsman Bass]

Out of curiosity, what's the safety measure here if there's a break in the space elevator length? Do you just have a thousands of kilometers (or longer) cable falling down across the Earth at terminal velocity, smashing anything it lands on?

[Terralthra]

The majority of it could also sail away out of orbit, if it breaks below the halfway point (which it most likely would).

[Elheru Aran]

I suspect that for precisely that reason a large strip of land might be enforced as agricultural only property-- no residential habitations-- and if it was located on an island somewhere nicely distant from anything else, that would help as well. Of course actually making it happen would be another can of worms.

Space elevators are not hype... but they're like the Alcubierre-drive Enterprise; we don't have the technology to get there yet and we aren't sure when we CAN do it. The theory and physics are practical enough, it's just putting forth the actual material effort that is another job entirely.

[Zixinus]

Wouldn't the part that would fall on the planet also burn up in the atmosphere?

[Elheru Aran]

Wouldn't the part that would fall on the planet also burn up in the atmosphere?

Some of it would, certainly. How much, I don't know. Would have to work out the ablative properties of the material used and how the dynamics of a massive anchored cable falling through the atmosphere would function. Not my area at all.

[andrewgpaul]

There are some simulations of a breaking elevator here (from the Wayback machine; the original website appears to have been taken down).

[Irbis]

Out of curiosity, what's the safety measure here if there's a break in the space elevator length? Do you just have a thousands of kilometers (or longer) cable falling down across the Earth at terminal velocity, smashing anything it lands on?

Why terminal velocity?

Thinking about this for a moment - you're thinking in terms of ground level gravity force. If the elevator breaks from impact, it will be above atmosphere, where it's not protected by air. It would take rather long time for anything to start moving quickly from such height, probably more that it would take emergency team to react.

For elevator to fall quickly you'd need to have sudden fault closer to ground - and even assuming such a thing can happen before vehicles moving on it spot weak section (NASA paper talks why multi-thread cable is in fact much more resistant to sudden failures) I don't think it would gather that much speed as the cable would be rather light and quickly slowed by aerobraking.

I even have gut feeling vehicles moving on thread at the time of collapse would be greater threat that elevator itself. And that assuming they wouldn't have a safety mechanisms of their own.

[Terralthra]

I think you overestimate gravity's force diminishment. Gravity at the surface of the earth is about 9.81 m/s/s. In LEO, it's fallen all the way down to....9.0 m/s/s. Even out in geostationary orbit, 35,800 km, it's still ~ .3 m/s/s.

If it breaks at geostationary orbit, you'd need to take the integral over r(4000m, 35,800,000m) of the curve F= GM/r^2 to find the total force at the moment of snapping, and remember that that half of the cable falling down has both a pretty substantial acceleration AND the jerk is always positive.

EDIT: Actually, thinking about it, the jerk would not be positive, because while some of the chain is falling faster and faster as it descends, some of the chain has already hit the ground and is thus not accelerating at all. It's a more complex equation than I gave it credit for at first. Another factor is the "falling chain" problem, where the already descended portion of the chain exerts greater force on the falling portion than gravity alone, "whipping" the end of the chain into the ground even harder than it would've fallen on its own.

[Simon_Jester]

Out of curiosity, what's the safety measure here if there's a break in the space elevator length? Do you just have a thousands of kilometers (or longer) cable falling down across the Earth at terminal velocity, smashing anything it lands on?

As noted, if the cable breaks below the halfway point, the upper half sails away into planetary orbit, where it poses a severe and unprecedented hazard to space navigation- I have no idea how you'd deal with that.

Normal space debris you can just vaporize with a big honking laser or something, in principle at least, but several thousand kilometers of carbon nanotube cable would present a number of problems in that respect.

[Don't assume that 'sails into space' equals 'harmless', in other words]

The other part will fall to Earth. On the other hand, the cable isn't necessarily massively heavy per unit length- indeed, there are a lot of reasons for it to NOT be massively heavy. If it is massively heavy it's probably multi-threaded, in which case the odds of all the threads failing at once is negligible unless someone does something insane like fire nuclear missiles at the cable.

That said, I'm not sure how well the cable would survive re-entering the Earth's atmosphere, which might well destroy the cable as it re-enters. Unless, again, it was stupidly massive, in which case, again, it'd be hard for any reasonable accident to break it.