Going up?

12 January 2019 | NewScientist | 42

Going up? Plans for a space elevator are getting a much-needed lift, says Kelly Oakes

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T MIGHT be in Indonesia. Maybe Brazil. Possibly on a barge floating in the Pacific Ocean. Wherever it ends up, somewhere on the equator the world’s tallest structure will jut out into space, a lollipop stick spinning with our planet as it makes its way around the sun. For a small but dedicated community of engineers, this is the future of space travel: an elevator shaft of Babel capable of transporting people and equipment directly into low Earth orbit. No more spectacular lift-offs, with their countdowns and explosions. Instead, a hundred thousand kilometres of off-key lift music as you and your fellow astronauts avoid eye contact at 100 kilometres per hour. It might not be the most glamorous prospect, but what it lacks in pizzazz it makes up for in offering cheap and clean access to space. For decades, the space elevator has been little more than a fantasy. The challenges have been overwhelming, including finding a material strong enough to sustain such a structure and working out how to get it into space. But over the past few years, some countries have begun making serious progress. In September, a team in Japan launched an experiment to test a cable system between two satellites in orbit, an early step towards figuring out how parts of a space elevator might work in practice. Obayashi Corporation, a major Japanese contractor, is aiming to develop an actual space elevator by 2050. Not to be outdone, China has its sights

the Earth end of the tether near the equator, where hurricanes almost never form. And to minimise collisions with floating pieces of former satellites, it should ideally be on a movable platform somewhere in the ocean. “You have to be able to move it out of the way of the satellites, out of the way of the space debris,” says space elevator consultant Brad Edwards. This would be much like a cartoon waiter carrying a towering stack of plates. Then you have the cabins to worry about. To work out the logistics of their movement, and ensure that nobody gets trapped between two floors 50,000 kilometres above the ground, researchers in Japan sent a miniature space elevator to the International Space Station in September for release into orbit. Two satellites 10 centimetres wide, tied together by an 11-metre steel cable, should now be passing a tiny climber back and forth while researchers monitor how the system works. Despite its small size, Yoshio Aoki of Nihon University’s College of Science and Technology says that the way the cable will be extended between these two satellites is similar to the way a space elevator would be built. “If this mission succeeds, the feasibility of the space elevator will increase,” he says. As for putting a full-size cable in place, Edwards has a solution. Put a satellite in orbit, loaded up with thousands of kilometres of wire, and have it dangle that payload all the way down to Earth’s surface. Then a small

between the atoms endow even a single tube with enough strength to theoretically hold up a space elevator. While single carbon nanotubes might be strong enough for the job, the longest made so far are only centimetres long – not a distance for which most people would bother taking a lift. To be useful, they need to be spun into cables, a process that tends to produce weaknesses. Rufan Zhang of Tsinghua University in Beijing, China, has found a way to overcome these weaknesses – but it is an artisanal process that will be difficult to scale up. He isn’t giving up, though. “I believe that the dream of space elevators will be realised after many years’ effort in this field,” he says. Another contender is graphene, the twodimensional lattice of carbon atoms that can be produced by peeling scotch tape off pencil lead. Often hailed as a wonder-material since its discovery in 2004, space elevators could give it the lift it needs to cement its reputation. In 2018, a team at Oak Ridge National Laboratory in the US grew single crystals of graphene that measured 5 centimetres in width by about 30 in length. An entire tether could, in principle, be manufactured in this way, but might take decades to produce. So why bother? For Peter Swan, president of the International Space Elevator Consortium, the answer is simple: to save the world. “When you can provide scalable, inexpensive and reliable access to space,” he says, “capabilities

mechanical climber would be sent up that wire, leaving a second ribbon behind. Repeat this process with ever bigger climbers, adding more and more ribbons, and you wind up with a sturdy cable leading from the ground to a graveyard full of climbers in the sky. These dead climbers could also have a second life as the counterweight needed to keep the elevator’s centre of mass from

“Satellites, astronauts and even tourists could get a quick lift into space” dropping below geostationary orbit. Previous proposals have included asteroids pulled into place specifically for the job, or a bunch of derelict satellites collected together in a big net. But Edwards sees the benefits of recycling. “You get several hundred tonnes of material at the upper end and it works out to be a great counterweight for the ribbon,” he says. So far, so good. The major sticking point? Finding a material to connect the sticking points. Because all of the components below geostationary orbit want to pull the elevator shaft down, and all those above want to pull it up, the tether will experience a phenomenal amount of tension. Make the cable thick enough and you could use any material, says Nicola Pugno at the University of Trento in Italy. But it’s not quite that simple, he adds. A regular steel cable would need to be almost a light year wide to keep from fraying. To have any hope of holding on to the top storey, we need something stronger. Edwards believes those kinds of super-substances are already out there. “We’re not selling the rope yet, but the materials exist,” he says. Top of the list of candidates are carbon nanotubes, two-dimensional sheets of carbon atoms rolled up into tiny cylinders. First engineered in 1991, the powerful bonds

emerge that will benefit those on Earth.” At present, transporting people and equipment into space is phenomenally expensive. NASA’s space shuttle programme cost $1.5 billion per flight, requiring millions of litres of fuel and littering the atmosphere with debris. By contrast, Edwards estimates that a space elevator would cost about $15 billion to construct, and could require very little external power. The energy it would need – to lift the cabins and ensure a corresponding movement in the counterweight – could come straight from the sun via solar panels fitted to the climber. Or, if someone wants to ride the elevator at night, giant high-powered lasers beaming energy straight up from Earth. With such potential benefits, it is little wonder Japan and China are pushing forward with their plans. So what’s stopping other countries from following their lead? Edwards thinks that a lack of political will is holding the space elevator back. Others say that there just isn’t the public appetite. “There is a consensus that people want to go to Mars now, or want to colonise the moon,” says Pugno. “But I’m not sure that they want to have a space elevator.” Edwards also thinks that for all their danger, expense and environmental downsides, some people just love rockets too much to give them up. “I sit on panels about space access with people who build rockets and they have absolutely no interest whatsoever in seeing a space elevator being built,” he says. Swan is ultimately optimistic. “Think of history,” he says. “In 1903, a piece in The New York Times estimated that it would take anything from 1 million to 10 million years for ‘mathematicians and mechanicians’ to achieve powered flight. Weeks later, the Wright brothers took to the air.” ■ Kelly Oakes is a freelance writer based in London

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TOTTO RENNA

set on building one earlier than that, by 2045. On paper, at least, the mechanics are pretty simple. Any object that orbits Earth, from artificial satellites to the moon, seems to experience a centrifugal force acting in the opposite direction to gravity. The higher the orbit, the stronger the force, and the weaker gravity’s pull. To keep an object from flying off into space, or crashing back down to Earth, the two need to balance out. Reaching that equilibrium is possible at any height, but depends on your speed of travel: lowerorbiting objects need to travel faster. To prevent the top floor of our space elevator from gradually shifting across the sky, it needs to orbit at the same speed as Earth rotates. That means its centre of mass needs to be some 36,000 kilometres over our heads, in a so-called geostationary orbit. In 1895, Russian scientist Konstantin Tsiolkovsky imagined a “celestial castle” orbiting Earth at this height, attached to the Eiffel Tower in Paris by a long spindle. The concept was ground-breaking – predating the first geosynchronous satellites by almost 70 years – but more stairway to heaven than space elevator. It was science fiction writer Arthur C. Clarke who popularised an elevator proper in his 1979 novel The Fountains of Paradise, inspiring future engineers. While Tsiolkovsky and Clarke imagined a structure extending to geosynchronous orbit, today’s engineers know a successful space elevator will need to stretch much further. Without a counterweight located further out in space, the mass of the cable and individual elevator cars will drag the structure’s centre of mass down too low to keep it in a stable orbit. Instead, we need a tether nearly 100,000 kilometres long, extending well beyond geostationary orbit, and strong enough to lift satellites, astronauts and even tourists into space. Keeping such an enormous structure safe would require creative thinking. To avoid the risk of gale force winds blowing the elevator shaft to bits, engineers have suggested placing