If an elevator stretching from Earth into space could ever be built, it could slash the cost of space travel. But a controversial new study suggests that building and maintaining one would be an even bigger challenge than previously thought, because it would need to include built-in thrusters to stabilize itself against dangerous vibrations.
Photos and video after the jump.
The idea behind a space elevator is simple. Deploy a cable stretching from the ground near Earth’s equator far enough into space, and centrifugal forces due to Earth’s spin will keep the cable taut.
Vehicles could then climb up the cable, also called a tether or ribbon, to get into space, powered by lasers on the ground or other Earth-based power sources. The idea could dispense with expensive rocket launches, making access to space much cheaper.
But the concept has been stuck on the ground floor for decades, not least because constructing a tether strong enough for the job is beyond current technology. Nanotubes might be up to the task, but they would have to be made longer and with fewer defects than any that can be fabricated today.
A new study makes the prospects appear even gloomier. Even if a space elevator could be built, it will need thrusters attached to it to prevent potentially dangerous amounts of wobbling, says Lubos Perek of the Czech Academy of Sciences’ Astronomical Institute in Prague. The addition would increase the difficulty and cost of building and maintaining the elevator.
Previous studies have noted that gravitational tugs from the Moon and Sun, as well as pressure from gusts of solar wind, would shake the tether. That could potentially make it veer into space traffic, including satellites and bits of space debris. A collision could cut the tether and wreck the space elevator.
People have previously considered the idea of smoothing out disturbances in the tether by making the Earth-based anchor for the tether movable, and jiggling it in carefully designed patterns to counteract the vibrations.
But Perek says that may not be enough. “Previous proposals for a passive tether controlled from the ground do not seem stable to me,” he said.
Anders Jorgensen of the New Mexico Institute of Mining and Technology in Socorro, US, who has previously studied the problem, agrees that stability is a concern for space elevators. But he says the new paper does not provide a quantitative analysis of the issue, and is not convinced that thrusters would be needed to stabilize the cables.
Earth’s magnetic field might naturally weaken any vibrations, though he admits it may not entirely eliminate them. Running electric currents through the cable might obviate the need for thrusters. And Jorgensen says he is not ruling out the possibility that a movable anchor could keep the disturbances in check.
If it turns out that thrusters are needed on the cables, he says they could pose a serious challenge to building a space elevator. “I am sure that having thrusters hanging off the cable at regular intervals is going to be a serious annoyance in terms of maintenance, refuelling, and simply the logistics of attaching them and having the elevator bypass them,” he said.
Bradley Edwards, who authored a detailed 2003 space elevator concept study for NASA, and was not involved in Perek’s study, says previous research suggests the Sun and Moon would only cause minor disturbances. He also cautions against the idea of attaching thrusters to the tether. “The complexity of operating climbers with hardware on the ribbon is serious,” he said.
Even if thrusters are needed, Perek thinks it is still worth pursuing the space elevator idea. “Its possible advantages are enormous,” he said. More detailed studies of tether disturbances need to be carried out to get a better idea of how many thrusters might be needed and at what positions along the tether, he says.
Via New Scientist