This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Fans of sci-fi author Arthur C. Clarke know and love his 1979 classic novel, The Fountains of Paradise. The plot centers on efforts of a visionary structural engineer in the 22nd century, Dr Vannevar Morgan, to construct a space elevator connecting the surface of the earth with a satellite in geostationary orbit, almost a kind of "cosmic sling" -- the better to raise payloads up there without relying on pricey rockets.
Clarke wrote The Fountains of Paradise nearly 20 years before the launch of the real International Space Station. He was all visionary like that. And he might turn out to have been doubly prescient if a space elevator ever becomes a reality. At the APS April Meeting in Baltimore this past week, West Virginia University physicist Leonardo Golubovic and his student, Steven Knudsen, unveiled a new twist on the concept for a space elevator that turns the usual schematic of a thin string connecting an Earth-based platform to geostationary orbit into a rotating loop.
The idea for a space elevator didn't originate with Clarke. As this 2006 guest post on the old Cocktail Party Physics blog points out:
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The original space elevator, as Clarke acknowledges, was first described by Russian engineer Yuri Artsutanov in 1960, in an article in Pravda called "To the Cosmos By Electric Train." Since then, it's apparently been independently "reinvented" at least three times:
(1) by a team from Scripps Institute of Oceanography and Woods Hole Oceanographic Institute (1966);
(2) in 1969 by A.R. Collar and J.W. Flower in the Journal of the British Interplanetary Society;
(3) and by Jerome Pearson of the Air Force Research Laboratory at Wright-Patterson Air Force Base (1975). It was hinted at, though not fully developed (for lack of a large enough envelope for calculations, he claims) by Clarke himself in 1963 in an essay for UNESCO on communications satellites.
There are several conceptual designs for a space elevator, but they all have the same basic components: a long tether anchored to an offshore floating platform and connecting to counterweight -- a satellite or space station -- in geostationary orbit, some 62,000 miles into space. Transport cars (for passengers or cargo) would be attached to the tether and move up and down as needed. How Stuff Works compares the concept to the game of tetherball: "[A] rope is attached at one end to a pole and at the other to a ball.... [T]he rope is the carbon nanotubes composite ribbon, the pole is the Earth and the ball is the counterweight. Now, imagine the ball is placed in perpetual spin around the pole, so fast that it keeps the rope taut. This is the general idea of the space elevator. The counterweight spins around the Earth, keeping the cable straight and allowing the robotic lifters to ride up and down the ribbon."
There's a lot to gain from a space elevator: using less power to move large payloads (thereby lowering costs), fewer adverse environmental impacts (electromagnetic power is better than exhaust from rocket fuel), plus it's quiet and the basic concept can be adapted and expanded -- in theory, that is. In actuality, the obstacles to making a practical space elevator are daunting, to say the least.
There's material issues for one: you need something incredibly strong to make that tether. Clarke invented a fictional "pseudo one-dimensional diamond crystal" with some trace element impurities for strength, grown in zero-g labs. That doesn't exist, but carbon nanotubes do, as well as that wonder material, graphene, which boasts not only great tensile strength but also the right electromagnetic properties. Most recently, excitement has mounted over a new diamond-like ultrathin nanothread that could prove ideal for a space elevator cable, but it's still in the lab -- Penn State University's John Badding's lab specifically -- and hence not quite ready for scaling up production.
Aye, there's the rub: as promising as these new materials are, they're not quite ready for prime time when it comes to deployment as part of a space elevator. And there's a host of other obstacles to surmount as well. The only workable locations on Earth are located along the equator, because that's where satellites line up the best in geostationary orbits. There are also few hurricanes or tornadoes, which could cause serious problems for that all-important tether between land and space. But the ocean is a far more difficult and unstable environment than most people realize, even under the best conditions.
Kevin Fong of the University College London told BBC Future in February that while he loves the idea of a space elevator, there would be safety as well as formidable engineering issues to making it a reality. "It paints a rather terrifying picture of a giant cheese wire scything through space taking out space vehicles and being itself hit by all the space debris up there," he said.
A start-up company called LiftPort is focusing its efforts on a lunar elevator, since conditions on the Moon are a bit easier to navigate, making it a great testing ground for a prototype space elevator. Back in 2012, the company (technically a consortium of companies) raised over $100,000 on Kickstarter to establish the PicoGravity Lab at a prime spot just between the gravitational fields of the Earth and Moon.
Back to Golubovic and Knudsen's rotating loop design: they first proposed this back in 2009 as a way to resolve how to supply energy to the climbing cars moving along the tether. Their thinking is that putting a spin on it, so to speak, would push things along the tether with no need for additional thrust, whether that thrust be from a traditional engine or pressure from, say, laser light.
Now they have new, more complex computer simulations thanks to cluster computing, demonstrating that such a concept need not be limited to an Earthbound elevator -- in fact, there might not be a need for a link to terra firma at all. The concept should work on gaseous planets, or those with softer, dustier surfaces that would pose a problem for anchoring a rotating space elevator. This kind of creative innovation is why Jen-Luc Piquant is personally all for professor/student collaborations right on the boundary between science and science fiction.
It all sounds like very exciting stuff, and I'm as much a fangirl as the next person when it comes to easy access to space, but seriously -- what are the odds of a space elevator becoming a reality in 10 years? In 2012 a company called the Obayashi Corporation announced it could build a carbon-nanotube based space elevator by 2050, but the general consensus is that this was largely a publicity stunt. Last year Google affirmed that it had considered a space elevator project, but decided it wasn't feasible. Yet.
"But we've made so much progress since 1979!" I can hear you all howl in protest. True! Just not quite enough progress. Check out the aforementioned long piece at BBC Future by Nic Fleming taking an in-depth, admirably clear-eyed look at the real-world prospects. Among his sources: That visionary's visionary, Elon Musk, who told MIT conference-goers last October, "This is extremely complicated. I don't think it's realistic to have a space elevator." He likened it to having a "bridge from LA to Tokyo," except that would be easier than a space elevator.
Granted, Musk has a vested interest in reusable rockets to deliver payloads -- Space-X just had another almost-successful test yesterday, in fact. A space elevator would represent serious competition. But he also has a pretty good grasp of just how difficult the remaining challenges might be to surmount. So if Musk is skeptical, perhaps we should be, too. That doesn't mean we can't hold out hope that Liftport could succeed where others have failed. "If somebody can prove me wrong, that'd be great," Musk told the MIT crowd.
And what about Clarke's visionary engineer? The fictional Dr. Vannevar Morgan dies of a heart attack just when his vision is about to become a reality. But wait! There was an epilogue, set several centuries into the Morgan's future, in which humans have abandoned a dying Earth to live on terraformed planets, and there is not one, but many space elevators connecting those planets to a central space station. He didn't live to see the full fruition of his idea, but he managed to catch a glimpse. Here's hoping the same will be true for us, too.
References:
Aravind, P. K. (2007) "The physics of the space elevator," American Journal of Physics 45 (2): 125.
Cohen, Stephen S.; Misra, Arun K. (2009) "The effect of climber transit on the space elevator dynamics," Acta Astronautica 64 (5–6): 538–553.
Fitzgibbons, Thomas C. et al. (2015) "Benzene-derived carbon nanothreads," Nature Materials 14: 43–47.
Isaacs, J. D.; A. C. Vine, H. Bradner and G. E. Bachus; Bradner; Bachus (1966) "Satellite Elongation into a True 'Sky-Hook,'" Science 11 (3711): 682.
Landis, Geoffrey A. and Cafarelli, Craig (1999) Presented as paper IAF-95-V.4.07, 46th International Astronautics Federation Congress, Oslo Norway, October 2–6, 1995. "The Tsiolkovski Tower Reexamined," Journal of the British Interplanetary Society 52: 175–180.
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Pearson, J. (1975) "The orbital tower: a spacecraft launcher using the Earth's rotational energy," Acta Astronautica 2 (9–10): 785–799.
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