Space Elevators

Podcast Transcript

You’ve probably seen footage of a rocket launch. There is a bunch of smoke and fire as the rocket lifts off to begin its flight to achieve an altitude and velocity which will get it into orbit.

It works, but it requires a lot of energy to get even a small amount of mass into the Earth’s orbit.

What if there was a way to travel into space that didn’t require a rocket? What if going into Earth orbit could be just as easy as going up to the top floor of a skyscraper?

Learn more about space elevators and how they could revolutionize space travel on this episode of Everything Everywhere Daily.

Getting into orbit is not easy.

If you remember back to my episode on the rocket equation, in order to get a kilogram of anything into Earth orbit requires a lot more than a kilogram of fuel.

You need a rocket, you need the fuel, but then the fuel needs to be sent aloft, which requires more fuel, and then that requires fuel, and so on.

The end result is that you need a big rocket to send something relatively small into orbit.

Rockets are expensive, dangerous, and can only be built so large. They are fine for putting something like a communications satellite into orbit, but if humanity wanted to do something much larger, like create massive rotating space stations or send humans to planets around other stars, we’d need something else.

But how?

If you remember back to my episodes on how satellites work, putting something into orbit isn’t so much a matter of altitude as it is a matter of velocity.

The reason why satellites have to fly so high over Earth is simply because we have an atmosphere. At the speeds you have to travel at to orbit the Earth, the friction caused by the atmosphere would make it impossible.

So, back to the question, how can you get something into orbit without a rocket?

What if you used a big gun? Could that put something into orbit?

That idea is not as crazy as it sounds. A giant cannon or a magnetic railgun could put something into orbit. The problem is that, unlike a rocket which gains speed over time, a gun starts at an extremely high speed and slows down through the atmosphere.

The payload would have to be at orbital speeds the moment it leaves the barrel of the gun, and the gun would be in the thickest part of the atmosphere near the surface.

What happens when something traveling at orbital speeds hits the atmosphere? It burns up.

Such a system could work very well if you were launching something from the surface of the moon, where there is no atmosphere, but not from the Earth.

So, once again, how can we get into space without a rocket?

About that speed thing. Getting into orbit is about speed. In low Earth orbit, a satellite will go around the Earth about once every 90 minutes. The high the orbit, the longer it takes to complete an orbit.

Keep going high enough, and eventually, the time it takes to orbit the Earth would be one day, the exact same time it takes for the Earth to rotate about its axis.

That point is known as geostationary orbit. Anything at that point will just hang over the same spot on Earth.

So, if you can get enough altitude, you can solve the issue of speed. You can use the rotation of the Earth to provide the velocity.

….but you need a lot of altitude.

To put it into perspective, the International Space Station sits at an average altitude of 400 kilometers or 250 miles above the surface of the Earth.

Geostationary orbit, however, sits at an altitude of 35,786 kilometers or 22,236 miles. Almost 100x times higher than low earth orbit, or to put it another way, almost three times higher up than the diameter of the Earth.

So we can reframe the problem. Instead of having to go really fast, we could get around it by just getting to a really, really, really high altitude.

However, that just creates a whole new problem. How do you go 35,786 kilometers straight up?

Maybe we could build a gigantic tower.

In theory, and this is just in theory, such a tower could work. However, it would have to be 44,700 times taller than the tallest structure ever built by humans.

The problem is there is a limit to how tall we can build something.

The larger the structure, the more weight. The more weight, the wider the base of the structure has to be. In theory, again, in theory, it could be possible to build something as tall as Mount Everest, but it would require a massive base to handle the compressive forces of gravity.

Even if we could build a structure so tall that it required a base the area of an entire hemisphere of the Earth, it wouldn’t be nearly tall enough to reach geostationary orbit.

So, we are back to our original question. How can we get to geostationary orbit without a rocket?

It turns out there might be a solution to the problem. In fact, the solution to the problem was first considered as early as the 19th century by Konstantin Tsiolkovsky, the same theorist that gave us the rocket equation.

Tsiolkovsky originally came up with the ideas that I’ve just gone through up to this point. He originally proposed the idea of a giant tower, but it was more of a thought experiment and as I just explained, as it isn’t actually possible.

No one took the idea seriously until it was revived in 1960 by another Russian, an engineer by the name of Yuri. Artsutanov’s insight was that rather than building a tower using the ground as its base, you could use a platform in geostationary orbit as the base.

From the platform in geostationary orbit, you could drop a cable down to the surface of the Earth. By putting a counterweight at a higher orbit, the center of mass would remain at a geostationary orbit.

Unlike the Tsiolkovsky tower, which would require materials with compressive strength, Artsutanov’s cable would require a material with tensile strength.

Artsutanov’s idea was unknown outside of Soviet circles because he wrote about it in Pravda, a Soviet newspaper that academics and engineers didn’t pay attention to.

In 1966, a similar proposal called “Sky Hook” was discussed in the magazine Science. While mostly a theoretical discussion, the authors did try to determine what material the cable could be made out of. Assuming the cable was of uniform width throughout, they believed that the material used would have to be twice as strong as any material currently known.

In 1975 a retired NASA engineer named Jerome Pearson, unaware of what Artsutanov wrote 15 years earlier, published a paper titled “The Orbital Tower: A Spacecraft Launcher Using the Earth’s Rotational Energy.”

Unlike the previous articles on the subject, which were just informal articles suggesting the idea as a thought experiment, Pearson’s paper was filled with calculations showing that such a structure could theoretically be possible, and moreover, his paper was written for a scientific audience.

The idea, while interesting, remained firmly in the realm of science fiction for another 20 years. Arthur C. Clarke had a space elevator in his 1979 book The Fountains of Paradise. Other science fiction authors used the concept of a space elevator as well.

Throughout the 80s and 90s, the idea of space elevators was mostly ignored.

However, in the 1990s, discoveries of new materials were made that changed attitudes toward the idea of a space elevator—carbon nanotubes.

Carbon nanotubes had properties, unlike any other material that humans had access to. It has a tensile strength orders of magnitude greater than steel or kevlar. It was so strong and lightweight that it could actually meet the requirements for a space elevator.

NASA held the first symposium on space elevators in Huntsville, Alabama, in June 1999, and from that, NASA published its first document on the idea titled “Advanced Space Infrastructure Workshop on Geostationary Orbiting Tether Space Elevator Concepts.”

After this, more and more time and attention was given to the idea of space elevators. The Elevator:2010 contest launched, which had cash prizes for teams that could develop technologies that could be used in a future space elevator.

Today, we are nowhere near being able to build a space elevator. However, the idea is no longer dismissed as being crazy. It has gone from being a thought experiment to today being more of a massive engineering challenge.

The biggest thing holding back a space elevator, other than an enormous amount of money, is materials science. While we can create carbon nanotubes, we can’t create them at scale, especially the scale required for something as massive as a space elevator.

But assuming that challenge can be overcome at some point in the future, what would a space elevator look like?

Here is a rough idea of how it would work based on several current proposals.

First, let’s start with the tether. It actually probably wouldn’t be a cable with a circular cross-section. It would probably be a flat and wide tape made out of a single massive sheet of carbon, probably in the form of graphene.

The length of the tether would have to be massive, not just extending up to geostationary orbit but far beyond that, as the center of mass has to be in geostationary orbit or, more likely, slightly higher. This would require either making the tether longer or putting a counterweight on the end.

The tether will have to deal with a host of forces, including atomic oxygen in the atmosphere, which could react with the tether, micrometeoroids that could hit it, winds in the atmosphere, the gravity of the moon, and the Coriolis force, more on that in a bit.

The tether would not be of uniform width. It would have to be constructed to be wider in geostationary orbit than it is at its ends. The need for tapering is to have more strength in the middle, where it will experience the most stress, and to have less weight at the ends, where there is less stress.

The tether will have to be attached to something in geostationary orbit, which would require the construction of a massive space station. In addition to anchoring the tether, it would need to be able to make small changes in its position to compensate for forces on the tether.

The tether needs then to have some base station on Earth on the equator. There have been several proposed sites for such a base. It could be outside of a major city near the equator, like Quito, Ecuador, or Nairobi, Kenya.

Another proposal would be to build a large platform in the Pacific Ocean that would be far away from populated areas.

The next thing would be the creation of a climber. This would be the physical object that goes up and down the tether. The climber needs to be as light as possible, but it also has to have the energy to climb all the way up to the top.

How to power such a vehicle is a challenge. One idea is to power it with lasers from the ground for at least the first 40 kilometers. The lasers would hit solar panels that would function off sunlight once it is beyond the atmosphere.

Another proposal would be to have some sort of power in the tether itself or to have a compact nuclear reactor inside the climber.

The speed of a climber would be limited. It couldn’t climb at the speed of a rocket. Assuming a climber could travel at the speed of a high-speed locomotive, about 300 km or 180 mph, it would take five days to reach geostationary orbit.

The reason for the limitation on speed is the Coriolis force. The top of the tether is going faster than the bottom of the tether. With every increment the climber goes up the tether, it is going slower than the part of the tether it is at.

That difference in speed will cause the climber and the tether to lean to the west, putting stress on the tether. If the climber were to move too fast, it could cause it to break.

This opposite would occur with a climber going down the tether as it would be faster than every incremental part of the tether it reaches.

There are a lot of problems to overcome before we could even attempt to create a space elevator. I’m pretty sure that one will never be built in any of our lifetimes.

If and when one were to be created, it probably wouldn’t be built on Earth. The easiest place to build it would be on the moon, which has less gravity and no atmosphere.

Nonetheless, the idea of a space elevator is a captivating one. If one were to be built, it would be the greatest engineering achievement in human history.

We are a long way from having the technology to build such a thing, but if significant advances in material science are made, maybe our great-grandchildren could one day live in a world where going to space is nothing more than getting in an elevator.

The Executive Producer of Everything Everywhere Daily is Charles Daniel.

The associate producers are Thor Thomsen and Peter Bennett.

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