Questions raised anew about space elevator stability

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. The violent shaking could potentially make the cable veer into space traffic, including satellites and bits of space debris. A collision could cut the tether and wreck the space elevator.

Engineers have 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 (this is similar to to the design of modern office sky-scrapers in earthquake-prone Japan: Rather than having rigid foundations, many of these buildings “sit” on top of huge springs, and the springs themselves are situated on rails; the spring-rail combination allows the building to move up and down, and right and left, to counteract and moderate the effects of a quake). Perek says that this may not be enough. “Previous proposals for a passive tether controlled from the ground do not seem stable to me,” he told New Scientist. Anders Jorgensen of the New Mexico Institute of Mining and Technology in Socorro, New Mexico, who has previously studied the problem, agrees that stability is a concern for space elevators. He says, however, that 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. Jorgensen also 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 told New Scientist. 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.

-read more in Lubos Perek, “Space Elevator: Stability,” Acta Astronautica 62, nos. 8-9 (April-May 2008): 514-20 (sub. req.)