Space elevators face wobble problem
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streb2001
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Again, predicted by the late, great Arthur C Clarke in "The Fountains of Paradise". Clarke's story actually suggested deliberately causing oscillations in a martian space elevator to allow Phobos to pass safely by (synchronous orbit for Mars is a greater radius than Phobos' orbit).
ED I won't spoil the story by saying how Clarke's engineer/hero solved the problem! /ED
ED I won't spoil the story by saying how Clarke's engineer/hero solved the problem! /ED
tblaxland
O-F Administrator
Highly recommended reading! As an engineer, I loved that book.
Andy44
owner: Oil Creek Astronautix
Space elevators face wobble problem
A disturbance travels up a space elevator cable in a simulation, with the horizontal scale of the wave exaggerated for clarity (Animation: David Lang, Software: Paul Snow)
[nomedia="http://www.youtube.com/watch?v=8TAcNvlUZBU"]Watch the full-size video[/COLO"]YouTube - Broadcast Yourself.[/nomedia]
Enlarge image
A space elevator would be more efficient than rockets, which fritter away much of their energy lugging their fuel up with them as they climb (Illustration: Pat Rawling/Liftport)
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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 stabilise itself against dangerous vibrations.
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.
Movable anchor
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 told New Scientist.
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 stabilise 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.
'Serious annoyance'
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 told New Scientist.
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 told New Scientist. 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.
Journal reference: Acta Astronautica (DOI: 10.1016/j.actaastro.2008.01.020)
- 16:34 28 March 2008
- NewScientist.com news service
- David Shiga
A disturbance travels up a space elevator cable in a simulation, with the horizontal scale of the wave exaggerated for clarity (Animation: David Lang, Software: Paul Snow)
[nomedia="http://www.youtube.com/watch?v=8TAcNvlUZBU"]Watch the full-size video[/COLO"]YouTube - Broadcast Yourself.[/nomedia]
Enlarge imageA space elevator would be more efficient than rockets, which fritter away much of their energy lugging their fuel up with them as they climb (Illustration: Pat Rawling/Liftport)
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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 stabilise itself against dangerous vibrations.
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.
Movable anchor
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 told New Scientist.
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 stabilise 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.
'Serious annoyance'
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 told New Scientist.
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 told New Scientist. 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.
Journal reference: Acta Astronautica (DOI: 10.1016/j.actaastro.2008.01.020)
n0mad23
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This oscillation/wobble problem has been raised fairly periodically for at least half a decade now.
What's baffling really is that it's 'controversial.' It's a BIG TAUT CABLE! Of course it's going to oscillate; the question really should be 'how badly?' and 'how do we address oscillation issues in other technologies?' 'Can we translate the solution in this application?'
I suspect there are other solutions to this problem other than strapping rockets onto the sides.
What's baffling really is that it's 'controversial.' It's a BIG TAUT CABLE! Of course it's going to oscillate; the question really should be 'how badly?' and 'how do we address oscillation issues in other technologies?' 'Can we translate the solution in this application?'
I suspect there are other solutions to this problem other than strapping rockets onto the sides.
Andy44
owner: Oil Creek Astronautix
I personally am of the opinion that the whole thing is pure fantasy at this point.
And as far as avoiding collisions with satellites goes, this thing would be on the equator, so any satellite in any inclination will cross paths with it at some some point. There's no avoiding it.
And as far as avoiding collisions with satellites goes, this thing would be on the equator, so any satellite in any inclination will cross paths with it at some some point. There's no avoiding it.
n0mad23
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It's true. And unless major steps are taken to address this one single problem, it will have to remain in the realm of pure fantasy.
The scale of such a project alone brings a host of problems of which satellite collision and oscillations only begin to scratch the surface. Wrap all the grand projects (including The Manhattan Project) into one, and the Space Elevator still would still just be getting underway.
I've yet to see a satisfactory (or at least unproblematic) solution to a climbing platform. Isn't it supposed to run both ways?
It's the same with periodic repairs - fairly abstract solutions without a lot of practical suggestions.
Still - what a fantasy.
silent_protagonist
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Maybe you could strap rockets to the climbers, and have them dampen the oscillations as they go. It probably wouldn't solve the problem completely, but it might help.
