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In principle, yes, but not with materials we can make today. A space elevator would need a cable stretching at least 35,786 km to geostationary orbit (ideally about 100,000 km), anchored to a counterweight in space. No known material is both strong and light enough; carbon nanotubes are the leading candidate, but we can’t yet manufacture them long or pure enough.
Over the last century, humans have done some rather amazing things. After the Wright brothers invented the first airplane in 1903, it took us only 66 years to send a man to the moon. Our engineering and scientific capabilities are clearly impressive, but perhaps it’s time we took a look at the challenges beyond anything previously imagined… maybe it’s finally time for a space elevator.
What Is A Space Elevator?
The concept of a space elevator was first theorized in 1895 by Konstantin Tsiolkovsky, the same gentleman who came up with the famous “Rocket Equation” (published in 1903), the foundation of how we send rockets into space (basically, his contribution to the space endeavor is enormous). Tsiolkovsky’s space elevator concept was inspired by the Eiffel Tower, which had been completed just a few years earlier, in 1889. He wondered if humans could build a tower high enough that its tip would extend far into space, so that instead of launching rockets to get there, we could simply hop aboard an elevator aboard this ridiculously tall structure and transcend the barrier of gravity to reach the stars!
At present, the tallest building in the world is the Burj Khalifa in Dubai, standing boldly at 829.8 m (2,722 ft). It became the tallest structure ever created by humans when it topped out in 2009, surpassing the previous record holder, the Warsaw Radio Mast at 646.38 m (2,120.7 ft), which stood as the world’s tallest structure for 17 years before it collapsed in 1991 during a botched guy-wire replacement. A feasible space elevator would have to be at least 35,786 km (22,236 mi) tall, the height at which an object reaches geostationary orbit around Earth. For comparison, if the Burj Khalifa was the height of a coffee cup (8.25 cm), then a Space Elevator would be 3.56 km tall, over 4.3 times the height of the actual Burj Khalifa!
What Would A Space Elevator Be Made Of?
Remember that 35,786 km (to reach geostationary orbit) is the minimum height we would need to reach for a space elevator to even function. The cable’s center of mass actually has to sit at or beyond the geostationary altitude; any lower and the system would be pulled back down to Earth. Ideally, the space elevator would be around 100,000 km (62,000 mi) tall. Think about that for a moment… the distance we’re talking about covering is practically 1/3rd the distance to the moon! At that distance, we would have to start building most of the elevator in space, along with several large spaceships and thousands of people working to construct the tower in zero-gravity.
Another way to do it would be to launch a giant spool of ribbon into geostationary orbit and then drop it down towards the earth, while another spool was released upwards (away from the earth) to counteract the force and stay in orbit. The original craft would stay in geostationary orbit and have long cables extending out in both directions. This idea seems like something straight out of a sci-fi novel, and it might as well be; the engineering and materials technology required for that sort of undertaking is much more advanced than we’re capable of currently.
A space elevator needs extremely high tensile strength to counteract the gravity that would be pulling this colossal 100,000 km structure down, as well as the centrifugal force and inertia of the counterweight (we’ll get to that in a bit) that would be pulling it up. It needs to remain stable and functional in extreme heat and cold, unpredictable forces from the atmosphere and radiation from outer space. On top of all that, it would have to survive micro-meteorites and particles from solar wind striking against it constantly. Does a substance that can tick the boxes on all those requirements actually exist? We think that carbon nanotubes might be the answer.
Carbon nanotubes are nano-engineered cylindrical carbon structures; we don’t find them naturally and they’re very difficult to create. They’re the stiffest and strongest substances discovered to date and they exhibit very high tensile strength, making them precisely the kind of stuff we need for a space elevator. They’re also electrically conductive, so we wouldn’t have to run additional wires to power the climber or the elevator.
So why don’t we have one already? The catch is that the cable doesn’t need uniform strength along its entire length; a real design tapers, growing thickest at geostationary orbit (where the tension peaks) and thinning toward each end. The figure that matters is “breaking length”: how long a strand of a material can hang before it snaps under its own weight. An untapered space-elevator cable would need a breaking length of roughly 4,960 km. In theory, carbon nanotubes reach about 5,000 to 6,000 km, which is exactly why they’re the leading candidate.
The trouble is the gap between theory and the lab. The best carbon nanotubes ever grown manage only a few millimeters to centimeters in length, and once you bundle billions of them into a real cable, defects drag the strength down by 70% or more, far below the threshold a working tether demands. So while the math says the right material is possible, we simply can’t manufacture it yet at the scale, length, or purity a space elevator would need.
The Counterweight
A space elevator will also need a counterweight at the top. In other words, the elevator will have to be attached to something very heavy, just as it’s attached to the earth at the bottom. The taller you build the elevator, the lighter this counterweight needs to be, in order to cancel out the additional mass that you’re adding to the cable itself. The counterweight is necessary to ensure that the mass above the height of Geostationary orbit and the mass below it remains roughly the same; therefore, the centrifugal force pulling the system upwards is equal to the gravity of it pulling downwards.
If we build a space elevator with the bare-minimum height of 35,786 km (22,236 mi), the counterweight would need to be enormous, because there’s almost no cable beyond geostationary orbit to do the balancing. The standard fix is to capture an asteroid and park it in orbit around the planet, then anchor the elevator to it. If humanity’s great engineers had been around 66 million years ago, maybe the asteroid that wiped out the dinosaurs could have been put to better use as a space-elevator anchor…
If your elevator climbs past about 53,100 km, the tip would be whipping around the planet so fast that letting go there would put you at escape velocity, the speed past which you fly out of orbit around Earth entirely. At that point, you could simply step off the elevator and coast toward the Moon, though your timing would have to be impressively precise to avoid drifting off into nothingness. From the far end of a 100,000 km cable, you’d have enough velocity to fling a payload all the way to Jupiter, if the stars (or planets, rather) align.
If It’s So Hard, Why Build A Space Elevator At All?
All these problems seem to come with very little payoff. Given the physical, scientific and economic limits, it seems practically impossible to build a space elevator. Furthermore, is it even necessary? We’re already able to send stuff to space, and there are people living on the International Space Station (although they’re in low Earth orbit at about 400 km, rather than 100,000 km). The answer is cost. Reusable rockets have already slashed the price of reaching orbit: the Space Shuttle cost roughly $54,500 per kg ($24,700 per lb) to low Earth orbit, while SpaceX’s Falcon 9 has pushed that down to around $2,700 per kg ($1,200 per lb) for customers. A working space elevator could in principle cut the cost of lifting that same kilogram to a tiny fraction of even today’s rocket prices, because you’d be paying mostly for electricity to climb a cable rather than for tons of expended propellant. That is the prize that keeps the idea alive.
Building a space elevator would be humanity’s most ambitious project to date. It makes the Wright brothers’ achievement seem small in comparison, although no less significant. Humanity always seems to find a way to outdo itself through its engineering prowess. We’re always looking for that next hurdle to overcome, that next challenge to conquer. Perhaps building a space elevator requires technology and manpower that we simply can’t dream of achieving today, but don’t forget that 150 years ago, flying was still a far-fetched dream for the human race. From that perspective, there’s really no telling how close we are to building a 100,000 km elevator to space!
