Are Space Elevators Really A Possibility?

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Remember that TV series, Foundation, where a space elevator collapses in a huge disaster?

EMPEROR: The tether wrapped around the planet like a garrote. It cut 50 levels down.

SPEAKER: Emperor, shut up.

IRA FLATOW: The concept of the space elevator is something we’ve covered over the years, many times, because everybody seems to love it. And every once in a while, a new proposal comes along to build one. Well, in case you’re new to this idea, here’s how it works.

Imagine a long cable stretching from the Earth’s surface to a satellite docked in orbit 22,000 miles high. Riding up and down on this cable would be a room, much like an elevator here on Earth, except this room would bring stuff, people, stuff up into space. This would make the need for expensive rockets we use obsolete.

Now, this is an idea that has been seen through science fiction books and movies for decades. Physicists have been thinking about space elevators since the late 19th century, but it has never been considered feasible, due to its projected exorbitant cost and engineering challenges it poses. I mean, you need a really strong cable to begin with, right? But the idea refuses to go away. A Japanese company, one of Japan’s biggest construction firms, the Obayashi Corporation, which built the Tokyo Skytree, had plans to build one in 2025, but has reportedly delayed that goal.

So what are the hurdles that keep it from being built? And why does it seem that, just like fusion, the space elevator is always 25 years away? Here to parse some of the problems is Dr. Dennis Wright, president of the International Space Elevator Consortium. He joins us from Santa Fe, New Mexico. Welcome to Science Friday.

DENNIS WRIGHT: Thank you. Thanks for having me.

IRA FLATOW: Did I get the concept right? Tell us what the parts of a space elevator would be.

DENNIS WRIGHT: You got it just about right. There is the cable, as you mentioned, and it would extend from the surface of the Earth to, actually, well past geosynchronous orbit. The geosynchronous orbit, or the geostationary orbit, is the key thing here.

It is that point in the sky 22,000 miles up, which would maintain the same spot over the place on the equator where the cable is anchored. And so that would be the place where you had a satellite, and a cable would be sent down from the satellite and one also sent upwards. And gravity and centrifugal force would stretch it taut and make it a cable which could be climbed by various craft.

IRA FLATOW: So the idea is that once you have a space elevator, it would be cheaper than rocketry to bring stuff into space, right?

DENNIS WRIGHT: Far cheaper, because you’re taking advantage of the rotational energy of the Earth, so you get a free ride most of the way, at least. You have to do an initial boost to get things going. Far cheaper than rockets. And also, the tonnage that you could put into orbit on a very regular basis is much greater than rockets, and also safer.

IRA FLATOW: Ideally, on Earth, on the Earth side of it, where would you like to locate it?

DENNIS WRIGHT: A lot of places have been proposed. But first of all, the equator. Somewhere on the equator is almost essential. You could go plus or minus 5 degrees and still have good lifting capacity, but the equator.

And then whether you put it on land or ocean is a debatable point right now, but it seems like the ocean is best because in the event that you do have a collision or some kind of severance event in orbit, part of the elevator may come down, and it would come down in the ocean. So that is the best place for it. And it also avoids local governments who might want to use the elevator only for their purposes, and other political aspects that would be avoided by putting it in the sea.

IRA FLATOW: So are you viewing this– is this viewed as an enterprise sort of thing?

DENNIS WRIGHT: We think it would probably have to be one of these multinational things, so it would hardly be private. And especially in the early going, where research funds are needed. So most likely, some kind of international cooperation would be required, at least in terms of international law. Because no matter where you put this, some international law would have to be dealt with. Space law, for example, is actually dealing with this issue right now, and trying to figure out what issues you’d have to address.

IRA FLATOW: So let’s talk about the challenges. What are some of the challenges that we are facing right now?

DENNIS WRIGHT: I think the first one is probably the one that most people know about, who have looked into the issue before, and that is the material. So in the past, there just were no materials strong enough to build a space elevator. So up till about 1991, at the discovery of carbon nanotubes, there was nothing strong enough that could support itself, let alone support payloads. And since then, three materials have come in.

We already had the carbon nanotubes to talk about, graphene, and hexagonal boron nitride. And each of these are strong enough. They exist. They’ve been made in the laboratory. They have strengths well beyond that of steel. And indeed, that was the impetus for a NASA advanced concept study in 2000, which really demonstrated the feasibility of a space elevator. But the challenge, then, is taking these materials from the laboratory and making them industrially, large amounts relatively quickly.

IRA FLATOW: But the material is strong enough, you’re saying.

DENNIS WRIGHT: About– if you– for an equivalent mass of steel, the graphene, for example, is about 200 times stronger, and that’s more than enough to support the cable and substantial payloads going into space.

IRA FLATOW: So how do you make sure, then, it reaches for hundreds of miles without losing its strength, needed to hold this megastructure together?

DENNIS WRIGHT: The key behind these materials is really the covalent bond. And so a lot of materials that we deal with on Earth are held together by Van der Waals forces, which are quite a bit weaker. But when we talk about graphene or carbon nanotubes or something like that, they are actually single molecules, and these single molecules are held together with covalent bonds, which are very strong.

In the real world, we never actually realize that strength, because the materials are composed of grains, and then the grains are put into layers. But when you have many, many layers of graphene, each of which is a single molecule, you’re taking full advantage of that strong covalent bond, and that never loses its strength. It doesn’t decay or lose any strength due to hysteresis or something like that.

IRA FLATOW: All right. And so how would you build the elevator itself? Would you build it down here on Earth and send it up in space, or do you build it in stages, going up and up and up? Or in space and then lower it down?

DENNIS WRIGHT: The best way, we think, is to transport rolls of this stuff into orbit at the geostationary orbit, and then pay out cables in opposite directions. So there would be one cable heading down toward Earth, another heading in the opposite direction. And you need that to make sure that the center of gravity is still staying at geosynchronous orbit. And that’ll vary from time to time as you do this, but that’s the key. And so we think that’s the best way. Send thin cables up and down, and then when they are in place, start laying laminates over those with more layers of graphene or what have you.

IRA FLATOW: If you’re sending cables up, how do you keep them from falling back to Earth while you’re building it?

DENNIS WRIGHT: That’s the key of keeping it in or near the geostationary spot, because if you lower cable from geostationary and then put cable up at the same time in the opposite direction, it will hold itself up. And so basically, you have this thing called gravitational gradient stabilization, and that means that it naturally wants to be straight up and down. Even if you knock it about a little bit, it’ll always come back to straight up and down. And if you’ve got the center of gravity near geostationary, then it’ll hold itself up.

IRA FLATOW: And so what powers the climber? Is it wheels on the room itself, moving up and down? Or how do you get power to move it up and down, into space and back down?

DENNIS WRIGHT: Two ways we’ve looked at. One is using wheels, so counter-rotating wheels that grip the tether and pull itself up. The other is maglev technology. There are maglev trains on Earth, which work very well and very fast horizontally. The problem is, how do you get that to work vertically?

And there may be some efficiency problems there, but people are still looking at magnetic levitation. And that’s probably ideal, because there’s no actual contact with the tether, and you’re using electromagnetic forces. But right now, we think maybe counter-rotating wheels is the best. Several of our people have actually designed a climber based on this concept, which could be built with materials that we have today.

IRA FLATOW: Would you be building just one elevator? I’m thinking of railroad tracks, right? You never build just one track, because you want to have things going in two directions at once. Would you do it that way, or just build a single track up and down?

DENNIS WRIGHT: There would be one track. And then the first thing you would do when you got that track is to build another one, because you always want to have A, a backup, and B, you’re probably going to add many more after that, in order to get significant amounts of mass into orbit. So I think the earliest implementation of this would be, probably, a set of six of them equidistantly spaced around the Earth. The idea is that you always have enough backup that you can afford to lose one.

IRA FLATOW: Could you turn the space elevator into a tourist attraction? And I mean, not just going up into orbit, but possibly halfway up? You might have like a rest stop or something like that.

DENNIS WRIGHT: Yes, there would be possibility for stations along the way. The tourist opportunity is certainly a great one, and they wouldn’t have to go all that high up. So that’s the nice thing about it. Wouldn’t take so long, and you could either pause the climber there and have them look around, or you would otherwise have to attach something to the tether, like a station, and have people disembark there. And going further up, I think the real commercial possibilities are at geosynchronous orbit. Because there, you’re far enough out of the gravity well that you can really go into the solar system.

IRA FLATOW: And how do we make sure the tether can resist damage from space debris, weather, radiation, stuff like that?

DENNIS WRIGHT: Yeah, lots of good questions, and we’re looking at those challenges. One of the things about graphene is it’s very tough, and experiments have been done, shooting bullets at it. And it’s very good at resisting bullets. It’s a lot better than Kevlar, which of course, is used in bulletproof vests.

So I know that orbital debris is a lot faster than a bullet, but the graphene could absorb many of these impacts without significant damage. There may be holes, which could be repaired later. That’s one of the aspects of it. The other is that, of course, we have a lot of space debris.

And we’ve done a study based on the trackable material in space, and so we know all those orbits, and especially the bigger ones. If the orbit is known, then you can set up a vibration in the tether so that it misses the object, let’s say, the Space Station, International Space Station, coming by. And you what that orbit is, and so just vibrate it out of the way and then it’ll come back, and you’ve missed it.

IRA FLATOW: What do you mean, vibrate it out of the way?

DENNIS WRIGHT: So the tether is stretched, taut, as I mentioned, but it is kind of like a rubber band, in a sense. It’s very tight, but it still will vibrate from side to side. So it’ll have modes of oscillation, like a violin string, and so there will be many different frequencies. Most of them will be very small, and the amplitudes will be small. But you can set up a vibration that still maintains the space elevator in a stable configuration, and that will allow you to avoid a lot of the space junk.

IRA FLATOW: You don’t want to start creating a vibration like on the Tacoma Narrows Bridge or that–

DENNIS WRIGHT: No, absolutely not. That’s a very good example. And one of the things you have to worry about, as you mentioned, radiation. If you do get a large solar storm, like a coronal mass ejection or something like that, that would be enough to set up vibrations in the tether, if it is very highly conducting. And so you have to make sure that the tether is either not conducting, or you know– have some warning that the storm is coming in advance, and you can counteract it.

IRA FLATOW: Interesting. How long would it take to get into orbit, if you’re on the elevator? You said it’s what, 200 kilometers an hour?

DENNIS WRIGHT: That’s probably the speed we’re looking at. We think that’s probably conservative. 300 might be more likely. At 200 kilometers per hour, it would be a week to get to geosynchronous. And then, obviously, much less to get to low Earth orbit. So you could go up and down in a day, if you went to low Earth orbit.

IRA FLATOW: And you mentioned that one of the reasons you would build it out in the ocean is because if it falls, no one on Earth, at least, would be hurt.

DENNIS WRIGHT: That’s right. And the science fiction scenarios that you pointed out are rather dramatic, but probably not too realistic. So assuming the rare case that we do get a split, or a severance in orbit, that is most likely going to happen at low Earth orbit, so that’s about 500 miles up. If 500 miles of the tether came down, then it would fall in the ocean, and you’re far enough from land that that’s fine.

It would also likely break up. As strong as the graphene or the other materials are, they might likely break up before they actually get to the Earth’s surface. So that particular danger of it wrapping many times around the Earth is not going to happen. The break in the tether would then cause the remainder of it, that is, the outbound part, that would slowly drift out into space.

And “slowly” is the key, because that could be rescued. You could actually tug that back into place, once you’ve got a repair mechanism in place. So I think the disaster scenario is not very likely, although there would be always the possibility of some kind of event that would bring part of it down. But we think it’s rare, based on our studies.

IRA FLATOW: I mentioned in the introduction that fusion energy is always 30, 25, 30 years away. And you know, it sounds like the space elevator is always 25, 30 years away.

DENNIS WRIGHT: Yeah, it seems frustrating, although we hope that we are on the exponential curve. It’s just the flat part of the curve right now, from the discovery of these materials. So graphene was discovered in 2006, I believe, right, specifically identified. And since then, there’s been a lot of progress.

So first of all, it was just a little grain that was taken off graphite with Scotch tape, and then it was produced in the laboratories. And as time goes on, bigger and bigger samples are being produced. Now there’s a piece of single crystal graphene, so a single molecule, about half a meter wide and half a meter long.

So the length is increasing. There are three companies, at least, that are manufacturing polycrystalline graphene, and these are in lengths of kilometers. So the lengths have been increasing quite a bit lately, and we think we might be on the increasing slope here.

IRA FLATOW: Is there enough international interest for a joint project to do this?

DENNIS WRIGHT: That’s a very interesting question, because we believe several countries are working on it, although some of them seem to have gone dark. So we know that work has been done in China. That is, in fact, that large piece of single crystal graphene I mentioned, was produced in China.

We haven’t heard much from them lately. South Korea has been doing quite a bit on this. And you mentioned earlier, Obayashi Corporation. They’re still quite interested. And yeah, so work is being done.

IRA FLATOW: Well, we will keep watching this, and please come back when you’ve got something new to report, Dr. Wright.

DENNIS WRIGHT: I’d love to.

IRA FLATOW: Thank you for taking time to be with us today.

DENNIS WRIGHT: And thank you.

IRA FLATOW: Dr. Dennis Wright, president of the International Space Elevator Consortium. He was joining us from Santa Fe, New Mexico.

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