SATURDAY, 29 JANUARY 2011Between 1958 and 1969, one of the most peaceful and productive conflicts in history raged. The so-called ‘space race’ pitted two superpowers against each other in frantic attempts to put the first man on the Moon, giving rise to iconic images of rocket launches and space shuttles. But why should today’s space exploration be based on such out-of-date technology? Rockets are exceptionally inefficient, with fuel-to-payload ratios exceeding 10:1. Each kilogram propelled into space costs tens of thousands of pounds, so an average astronaut takes close to a million pounds just to reach orbit—without any equipment.
So how can we get out of our technological rut? Science fiction has been contemplating a myriad of possibilities for decades, but one stands out, so much so that NASA has started studying its feasibility. First popularised by Sir Arthur C. Clarke in The Fountains of Paradise, the concept of a space elevator is delightfully simple: a satellite extends a rope, commonly called a tether, all the way down to the ground, where a machine (the ‘climber’) grabs onto it and starts the long haul all the way to the top.
Although this sounds suspiciously easy, the challenges involved are staggering: the satellite would have to be in geostationary orbit, 36,000 kilometres above the surface of the Earth, which makes for a rather lengthy cable. Additionally, the tether cannot just be lowered to the ground. A counterweight thousands of miles beyond the geostationary orbit must be used to keep the construction in equilibrium and stop the satellite from falling out of the sky. The tether must be able to support its own weight, which leads to the biggest hurdle. No practical material exists that is strong enough to bridge such a distance and support its own weight without snapping—at least, not yet. Scientists are investigating novel materials, called ‘carbon nanotubes’, which have a theoretical strength hundreds of times greater than steel with only a fraction of the density. If these could be manipulated, mass produced and woven together into a continuous fibre, the cable would no longer be a physical impossibility.
However, it is not just the tether that imposes technical constraints. Due to the huge distances involved, the climbers would have to travel at high speeds to make the journey in a reasonable amount of time. For example, for one week’s journey, the pod must average 215 kilometres per hour, travelling vertically upwards, and maintain this speed against the effects of gravity. This requires large amounts of energy, but carrying a power source into orbit creates exactly the same problem as launching rockets: a huge fuel-to-payload ratio. One intriguing possibility is the use of so-called ‘beamed power’. This uses a high-intensity Earth-based laser to illuminate a modified solar panel on the climber. Accurately illuminating a spot a few metres across from a distance of 36,000 kilometres may be tricky, especially when the spot is moving at hundreds of metres a second. Fortunately, NASA is on the case, offering a $2 million prize in a competition to do exactly that, albeit on a slightly smaller scale. In their contest, the cable is lowered from a helicopter hovering a kilometre above the ground, and the climbers must ascend to the helicopter in under three minutes.
Smaller prizes were offered for breaking easier time barriers at four and five minutes. As of 2009, a time of 3 minutes and 49 seconds has been achieved, winning 900,000 USD, but the top prize remains up for grabs.
The mini-elevator used in this competition was elementary to build: hanging a steel wire from a helicopter is not exactly a miracle of engineering. By contrast, constructing a full-scale working space elevator would be quite an impressive feat. A cable of this length would be expected to weigh thousands of tonnes (even if it is made of materials such as nanotubes) and cost billions to lift into space with rockets. The cable would have to be fragmented—no single rocket could lift something that heavy. There is, however, a much more sensible alternative. Once the elevator is in place, it can be used to send material into orbit at very low cost—so why start big? A rocket could be used to send a 22—tonne ‘seed’ cable into space. This would be full length, stretching all the way back down to Earth, but so thin that it would barely be visible. An extremely light climber, whose only payload is another cable, could then climb this ‘seed’. When spliced to the first, the resulting, stronger cable could be climbed in turn by a larger climber, carrying a heavier cable to add to the first two. Hundreds or even thousands of iterations later, the elevator would be hefty enough to take a real payload—a satellite or even a pod carrying astronauts.
Once we are capable of lifting pods with humans in, the possibilities of the space elevator become boundless. Quite apart from offering users an extraordinary cost advantage over those still stuck with classical rockets, an elevator can very simply be scaled up until it can take hundreds of tonnes at a time. Space tourism takes on an entirely new meaning when, rather than experiencing the cramped confines of an all-too-brief rocket trip, individuals are offered a luxury two—week tour in a large capsule with panoramic views. Satellites would also be designed with cheaper budgets, capable of being readily lofted into space for any scientific or financial end. The advent of rockets brought us satellite TV, GPS and the iPhone. Perhaps the space elevator will usher in a new wave of innovations, with as-yet unforeseen consequences.
A few rather sizeable hurdles still stand in our way. Although the technical challenges are considerable, economic issues and public opinion pose just as great a threat. Any government who stepped into the fray would struggle to justify the costs to their voters, despite the potential benefits. The international ramifications of building such a structure, with its huge military advantages yet equally large military vulnerabilities, would lead to a political quagmire. An extremely brave, and possibly foolhardy, politician would be required to head the project. However, if all of this could be overcome, the space elevator could open the door to a space-faring future. When might this be? As the late Sir Arthur C. Clark used to say, the first space elevator “will be built 50 years after everyone has stopped laughing.”
Mark Nicholson is a 3rd year undergraduate in the Department of Chemistry