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Future of Space Elevator Looks Shaky
Posted by
kdawson
on Tue Dec 09, 2008 01:43 PM
from the a.-c.-clarke-quaking-in-his-grave dept.
from the a.-c.-clarke-quaking-in-his-grave dept.
lurking_giant writes "In a report on NewScientist.com, researchers working on development of a space elevator (an idea we have discussed numerous times) have determined that the concept is not stable. Coriolis force on the moving climbers would cause side loading that would make stability extremely difficult, while solar wind would cause shifting loads on the geostationary midpoint. All of this would likely make it necessary to add thrusters, which would consume fuel and negate the benefits of the concept. Alternatively, careful choreography of multiple loads might ease the instability, again with unknown but negative economic impacts."
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Hardware: Space Elevator Teams Compete for NASA Prizes 158 comments
Hugh Pickens writes "The University of Saskatchewan's has the first place climb in the Second Annual Space Elevator Games being held this weekend at the Davis County Event Center in Salt Lake City. Teams are competing for $1,000,000 in NASA prize money. Although the idea of a space elevator has been around for decades, the space technologies needed to support it have yet to be created. The non-profit Spaceward Foundation has hosted an annual competition since 2005 to build a super-strong tether, or get a robot to climb a suspended ribbon. In the robot climber competition, teams have to get their device to hurtle up a 100-metre-long ribbon, suspended from a crane, at an average speed of two metres per second. The climber must be powered from the ground: strategies include reflecting sunlight from huge mirrors on the ground to solar panels on the climber; shining lasers from the ground up to similar panels on the robot; or firing microwaves up at the climber. Qualifying rounds have been taking place all week, and although high winds and rain have caused delays, four out of eight teams have made it into the finals. There are no outdoor climbs today because of bad weather but some of the tether competitions will happen indoors later this afternoon."
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Technology: Japanese Begin Working On Space Elevator 696 comments
thebryce writes "From cyborg housemaids and waterpowered cars to dog translators and rocket boots, Japanese boffins have racked up plenty of near-misses in the quest to turn science fiction into reality. Now the finest scientific minds of Japan are devoting themselves to cracking the greatest sci-fi vision of all: the space elevator. Man has so far conquered space by painfully and inefficiently blasting himself out of the atmosphere but the 21st century should bring a more leisurely ride to the final frontier. Japan is increasingly confident that its sprawling academic and industrial base can solve those issues, and has even put the astonishingly low price tag of a trillion yen (£5 billion) on building the elevator. Japan is renowned as a global leader in the precision engineering and high-quality material production without which the idea could never be possible."
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Told you so (Score:5, Funny)
I told everyone it wouldn't work. But would they laugh at me? No!
Re:Told you so (Score:5, Interesting)
Most of the inner planets have no space elevator at all; Venus and Mercury because their days are unfeasibly long, Earth because its gravity well and debris belts challenge the limits of engineering.
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Re:Told you so (Score:5, Insightful)
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Re:Told you so (Score:5, Interesting)
I told everyone it wouldn't work. But would they laugh at me? No!
I know you were joking, but I really think it won't work for reasons not specified in the article. It's such a simple reason that I can't believe it's so rarely mentioned or addressed.
The earth is built very much like a capacitor. The ground has a fairly strong positive charge and the ionosphere has a fairly strong negative charge, with an insulating layer of air in-between. Carbon nanotubes can conduct electricity; so can most other materials I have heard of that would be used for a space elevator. I imagine that any conductor (and possibly dielectrics also when you consider electrical breakdown and the sheer current involved) would vaporize as soon as this circuit is closed. Coriolis forces and weight distribution and whether thrusters would be necessary seems trivial by comparison.
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Re:Told you so (Score:5, Interesting)
The earth is built very much like a capacitor...
So use the current flow. You're breaking the earth's magnetic field lines with the cable. Not a lot of field strength, but it's a lot of field, sounds like a generator to me. Ship up the necessary kilograms of (i don't know, zinc perhaps) sacrificial anode and dump the potential via ions accelerated as lateral thrusters running continuously, and vary the flow in any particular direction to adjust the position of the cable terminus. The spare current could run the elevator cars.
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What could go wrong? (Score:5, Funny)
I am confident there will be no problems. Ship it.
Signed,
Bill "Shakey" Bradson
Lead Engineer, Tacoma Narrows project
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Re:Told you so (Score:5, Interesting)
If the reason for coming with such a thing as a space elevator(which I agree is pretty impossible with any material currently known) is to cut down on the cost of getting things into space then why hasn't anyone been looking to build a "supergun" like Gerald Bull [wikipedia.org] had experimented with ages ago? It just seems logical that if you built it at the equator you could cut down on fuel required by using a gun style launch and then having the thrusters kick in at the top of the arc and use the momentum to assist getting the vehicle into space. And if we could build it as a magnetic coil or rail gun we could save even more by using electricity, which is easier to produce, than chemical engines.
So is there anyone looking at the "supergun" concept? or did the idea die out with Bull?
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Re:Told you so (Score:5, Interesting)
The space gun concept would really only be good for a very narrow range of payloads that can withstand the extreme g-forces produced by such a device. You can reduce the g-forces by using a longer barrel but it's still a concept that really isn't feasible.
What we should be looking at is a Space Fountain [wikipedia.org]. Yes, it seems like a very odd idea but it's backed by a lot of very good science and a lot of people are saying that it can be done with present materials and technologies. At the very least we should be experimenting with them on a smaller scale, using them to erect temporary masts and towers.
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Most great breakthroughs start with 'crazy' ideas (Score:4, Interesting)
People who don't know, or who refuse to accept that things are 'imposible'. They're the ones who drive progress. Think the Wright brothers, Einstein or better still Michelangelo, who imagined flying machines and submarines that were only inviable because the necessary technology (engineering & materials) were not available.
After all, geosync orbits were thought up by first by a scifi writer...but to your point, Arthur C. Clarke did have a good grasp of Physics...
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What about the glass elevator? (Score:3, Funny)
Alterantives (Score:5, Funny)
If an elevator won't work what about a space escalator?
Re:Alterantives (Score:5, Funny)
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Re:Alterantives (Score:5, Funny)
/me runs off to patent the "Space Canoe".
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Serious Alterantives (Score:5, Informative)
In all seriousness, the space elevator gets a lot of press because it's the concept that is easiest for the average person to understand, that doesn't mean it is the only option (or even the best option) to efficiently get stuff into orbit without rockets. I always thought the launch loop made more sense (http://en.wikipedia.org/wiki/Launch_loop/ [wikipedia.org]).
The idea is that the moving parts are what keeps the structure stable, rather than tension or compression. In theory it could be built with today's materials and technologies and could be cabable of launching more into orbit in its first month than has been launched to date with conventional rocket launches.
Then of course, there are the non-traditional rockets such as laser propulsion, where a laser is shined up from the ground to superheat the air in the rockets cone, which, in turn, produces thrust. And of course, my personal favorite, there's always Project Orion. Not the wimpy one NASA is using to get to the moon, I'm talking about the original Project Orion. As in, using thermonuclear bombs to launch a city sized spaceship into orbit.
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The best part is.. (Score:5, Funny)
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Re:Alterantives (Score:5, Funny)
But when you get there the shops are all closed. Bollocks to that.
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Re:Perhaps a zepplin? (Score:4, Informative)
Speaking of which, there is an airship to orbit concept that was discussed here a few years ago.
You have two airships, a ground ship and an orbital ship. You put your payload on the ground ship where it ferried to a high altitude rendezvous with the orbital airship. The orbital airship raises the payload farther, to the highest point it can on buoyancy. That point is far below orbit, but the atmosphere there would be thin enough to permit the use of ion thrusters. Ion engines take the airship to orbit: a two week process. To return payloads from orbit the process is reversed.
Personally, I don't think this would ever prove to be practical, but it is possible to imagine it working.
The outfit behind this concept (JP Aerospace [jpaerospace.com] seems to be a volunteer organization of high altitude balloon enthusiasts. They've done a number of spectacular balloon missions, in one case sending a balloon to over 19 miles, or 1/3 of the way to the official "space" line. They don't seem to have done anything in the last year though.
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Don't forget the ninjas (Score:4, Insightful)
Re:Don't forget the ninjas (Score:4, Funny)
First, GP:
There's also the problem that any ninja can come along and cut the cord
I think it'll survive a katana if it can survive the other stresses being placed on it.
It's a ninja. A ninja can use any weapon he likes and will be able to cut the thing if he pleases
Well, the base would be mobile too -- in the ocean. But I see your point.
AHA! Ninja problem is solved. Surround the base with pirates!
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Re:Don't forget the ninjas (Score:5, Funny)
Wait till it 30.. it'll stabilize around then.
Unless she's still single. Then she'll start collecting cats.
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Re:Don't forget the ninjas (Score:4, Funny)
And since she's Physics, she'll name them all Schroedinger.
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Re:Don't forget the ninjas (Score:5, Funny)
Maybe we just can't SEE the hyper-dimensional space whales.
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Scary stuff (Score:5, Interesting)
You think the engineering is mind boggling? (Score:5, Funny)
Your mind will be hyperboggled by the amount of paperwork, business trips and expense account lunches the project will generate. The engineering will look like chump change.
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Re:Scary stuff (Score:5, Funny)
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Re:Scary stuff (Score:5, Insightful)
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Re:Scary stuff (Score:5, Funny)
Take a ball of paper and throw it at 100,000 miles an hour. Tell me that's not going to cause some damage.
For starters it's really going to strain your arm.
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Re:Scary stuff (Score:5, Informative)
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Re:You forgot Apollo 1 (Score:5, Funny)
Apollo 1 doesn't count, as NASA declared a mulligan.
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Rockets to the rescue? (Score:3, Interesting)
Why not compensate for Coriolis force by using rockets?
Coriolis force is tiny, so we won't need a lot of reaction mass.
Probably, it can be used together with multiple loads choreography for greater effect.
I call bullshit! (Score:3, Informative)
The coriolis effect is not a real force. It's an illusionary effect that happens when you have a moving point of reference. As to solar winds and stuff; can you be a little less vague. Let's say for a 10 meter thick cord, white color, how much force would be imparted on the cable over its length? Is the concept currently economical? No, and that's hardly news. Is it unstable and unworkable? Well... if you're pinning your conclusions something that doesn't actually exist to answer that, I think you might have a problem.
Re:I call bullshit! (Score:5, Funny)
Obligatory xkcd reference: http://xkcd.org/123/ [xkcd.org]
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Re:I call bullshit! (Score:5, Informative)
You are right, but you are wrong. The Coriolis effect is very real, but it is not force in the strict sense.
The gist of the point in the article is that as a payload is moved up the elevator, it must be accelerated to the side, since the upper portions of the elevator are moving circumferentially faster than the lower portions. The force required to accelerate the payload must come from the elevator itself, causing small displacement of the elevator. The use of the term "Coriolis effect" is not strictly wrong, though it is somewhat sloppy.
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Bah (Score:3, Funny)
No one said it would be easy.
Re:Bah (Score:4, Insightful)
The Rocketdyne F-1 engines on the first stage of the Saturn V had a similar problem early in development. They had a nasty tendency to ring like a bell until they disintegrated (being very loose with this description for the sake of illustration). And they fixed it. The end design was incredibly stable and self damping. With little more than pluck, slide rules, and raw engineering talent. Hell, the entire computer facilities available to NASA at the time (late '50's to early '60's) were less than are available on any engineers desk today.
Solving supersonic flight was another issue of instability. The planes had a tendency to shake themselves apart. We solved that one with essentially no computer help at all (late 1940's).
I have confidence that this problem is solvable. It may not be easy, and may take some genius, but it is solvable.
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Fixed thrusters rockets (Score:3, Interesting)
Nobody said this would be easy (quite the opposite), and nobody is claiming we're even close to being "there" yet. But is the space elevator dead? No. Just still working out the kinks. Look, have you any idea of the number of launches required to prepare, by tiny increments, for the eventual (and still debated, snicker) moon landing? We'll get there, eventually.
Even with thrusters, it's bound to be a better long-term solution than rockets. Especially using ion drives, you could hard-wire the fuel supply from down below, so to speak, and so not need to haul that mass, too.
Re:Fixed thrusters rockets (Score:5, Informative)
Ion drives need physical fuel as well as power... they just are a lot more efficient than traditional chemical-reaction drives. This is because they accelereate the fuel to near-lightspeed, maximizing the reactionary force per kg of fuel. (force is a combination of the mass expelled and the speed of which it is expelled... the faster the exhaust, the higher energy per kg of exhaust).
So, you'd still have to haul up fuel, just not as much as with chemical rockets.
MadCow.
Parent
ACC already covered this... (Score:3, Informative)
...,kind of, sort of, in Fountains of Paradise.
In that novel he proposed timing the departures of loads for a space elevator on Mars. Not to damp oscillations, in this case, but to cause them. By timing the oscillations correctly, the elevator would oscillate out of the way of the moon Phobos, which orbits lower than the Martian geosynchronous orbit.
Shaky? (Score:4, Funny)
Yep, anything 24K+ miles long and thin as a wire and zipping through the upper reaches of the atmosphere would probably be "shaky"....
Just jump. (Score:5, Funny)
there goes another dumb jet pack idea (Score:5, Interesting)
Re:there goes another dumb jet pack idea (Score:4, Informative)
At 2G the entire way, that rail would have to be 1600km long, and would have to rise >20km into the atmosphere to prevent annihilation by friction.
Even at 4G, the track would have to be 400km long.
Frankly, I am not sure that this project would be any more realistic.
Parent
Having read the article... (Score:5, Informative)
Their big objection seems to be not that the forces on the elevator are unmanageable but that oscillation could lead to payloads being released into orbits that are "10 km" too high or too low, or that the oscillation could put the elevator in the path of a satellite. Correcting that would require thrusters.
For the first, surely you could simply time your release with the oscillation, to get into the orbit you want. Even if you couldn't, the space elevator would be good for putting things in geosynchronous or interplanetary transfer orbits. The cost of a bit of propellant to correct a +- 10 km error is pretty minor compared to getting into one of those orbits in the first place.
For the second, thrusters to purposely oscillate the cable to allow it to dodge out of harms way are a pretty standard part of any space elevator proposal. That is, the ability to move the cable a little is a desired, even necessary part of its design.
The internet makes playing "telephone" boring (Score:5, Informative)
The "Space Elevators are unstable! The concept is doomed!" Slashdot summary would have been much more thrilling if there wasn't a link to the "Space Elevators are tricky! There might still need to be tiny final orbital adjustments!" New Scientist article, and even that would have been more exciting than the "Space Elevator dynamics is modeled by these stable but undamped equations! Sending multiple payloads up in the right phase causes the minor Coriolis-induced wobbles to cancel out!" Acta Astronautica article.
You people with your damn hyperlinks are ruining journalism. It's getting so a guy can't even wait breathlessly for the News At 11 anymore to find out what common household product might be Killing Our Children.
Of course (Score:4, Funny)
Why hasn't this problem come up sooner...? (Score:4, Interesting)
It's a given that a elevator would be tethered at the equator, thus will be traveling at 1600kph, the velocity of geosynchronous orbit is what, 11000kph? Anything climbing from the bottom up will be accelerated to that as it ascends. So the question is how the hell do you mitigate this without literally bending the thing out of shape - burning fuel is silly It's not a trivial velocity, it's 40% of what would put you into LEO orbit anyway!
Despite this, I don't think this is a showstopper, remember Arthur C Clarke told is it will be built...
A Rotating Skyhook doesn't have that problem. (Score:4, Informative)
A rotating skyhook (a rotating line connected to a ballast on one end and a payload on the other) wouldn't have that problem.
http://www.nss.org/settlement/L5news/1983-skyhook.htm [nss.org]
But a rocket hook combination makes the most sense right now, it would reduce the launch weight by removing the need for the vehicle to accelerate itself all the way to orbital velocity.
Re:A solution to coriolis force (Score:4, Informative)
if the top of the elevator isn't in geo-synchronous orbit, the elevator has to be a free-standing structure. You can only put stuff in geo-synch on the equator...
Good luck with that!
Parent
Re:No energy saved (Score:5, Informative)
So much wrong, so little time...
Sorry, most of your post is factually challenged.
1) Space elevators do not lower the energy required - they just use the energy differently.
2) They do not take you to where the gravity is weak - they take you to the point where the force of gravity (which is essentially unchanged) is balanced by centripetal force (which, being linked to w^2r goes up linearly with distance).
3) Rockets typically take you to about 7.7 km/s (orbit), not 11.2km/s (escape).
4) The energy given to the satellite (assuming the same final orbit) is identical regardless of the launch vehicle/elevator used. What is different is the energy efficiency of the system in putting energy into the satellite:
A rocket sends lightweight propellant in the opposite direction very fast in order to transfer the energy. An elevator sends a huge mass (essentially the entire earth) very slowly in the opposite direction. Since momentum is conserved, the mass x velocity of both systems is the same - but since the Earth masses a lot more than most rockets, the Earth's relative velocity is far lower. This is where the e=0.5*m*v^2 comes in - the "wasted" energy is the energy provided to the Earth or propellant. Earth has a small v, big m - which works better than the rockets big v little m.
So you always have to give the satellite the same energy - there are just different efficiencies of giving it that energy. Space cannons have the problem of needing to give that energy extremely quickly... very difficult indeed.
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Re:No energy saved (Score:5, Informative)
Earth's gravity is substantially weaker at GSO. GSO altitude is large compared to the Earth's radius.
Space elevators *do* lower the energy that is supplied by the launch system.In a space elevator, the energy for the sideways motion comes from the rotation of the Earth (hence the Coriolis forces on the elevator mentioned in the summary). For GSO, that's less than the energy spent climbing up the gravity well, but it's still not trivial.
For escape trajectories, the elevator looks even more attractive -- once you pass GSO, the ride becomes free, and you gain energy from the dynamics of the system without spending any propellant / electricity / whatever. Time it carefully, and you just "fall" off the end of the cable on the right trajectory.
All of that said, rockets aren't *that* inefficient. For LEO, they can be 10% efficient or better (slightly worse for GSO). That's not great, but there are no proposed methods of getting energy to the elevator car that are all that efficient either, especially when you count electricity generation losses. Given the disparity in capital costs, and the fact that in neither case is the energy cost a noticeable fraction of the budget, I suspect rockets will win out for some time to come...
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