Space Elevator May Become Reality 465
mojotek writes: "The NASA Institute for Advanced Concepts has a study(15Mb pdf) about the feasibility of a "Space Elevator" comprised of a 22,000 mile long cable built out of carbon nanotubes. In theory, it would be able to carry loads of 20 tons to space without using a single rocket engine. Sounded way too sci-fi for my taste at first, but this article at TechTV actually helped fill in the holes."
[ding] 345,234th floor... (Score:2, Offtopic)
Meet George Jetson! (Score:2, Insightful)
Re:Meet George Jetson! (Score:2, Informative)
Also, you can transfer fuel up by the tanker load.
Re:Meet George Jetson! (Score:5, Insightful)
Not really, because the "efficient" propulsion systems probably won't be able to lift a rocket off the ground. E.g. the DS-1 ion engine, high efficiency but only about 0.1N of thrust - or nuclear engines that would be too dirty to run in the biosphere, but would work fine in interplanetary space.
If a space elevator could be built, the cost of lifting payloads into space could drop dramatically, and that would create a lot more incentive for companies to develop these efficient space-only engines.
Re:Meet George Jetson! (Score:5, Informative)
If you want to leave earth orbit, you take a second elevator that runs from geostationary station out to the anchor and let go. Depending on the length of this section, you'll have a ballistic launch to anywhere else in the solar system. Well, you'll need a modest amount of fuel unless the plane of earth's orbit is exactly aligned with your destination, but you'll need orders of magnitude less fuel than you need today, and you can get that fuel up to the launch point for the cost of electricity alone.
If you want to leave the solar system, you let go of the upper elevator and hop to the center of a freespinning tether, then inch outward. When you reach the end of this tether, you could be traveling at a few percent of c. You'll be at Alpha Centari within 100 years... and a second tether there could capture you and slow you down. That's too long for passenger traffic, but brief enough that interstellar colonization is a realistic possibility by the end of the millennium.
So all things considered, I think research into carbon nanotube space elevators has better long term potential than anything rocket propulsion technology. Even antimatter propulsion, excluding some unknown mechanism to mass-produce anti-atoms.
already been tried (kind of) (Score:2, Informative)
Well, they goofed up the math somehow. They underestimated the stresses on the cable and the thing snapped shortly after deployment, flinging it away from the shuttle. They did not retrieve the cable; one more piece of space junk.
Re:Meet George Jetson! (Score:4, Informative)
There're two significant challenges in implementation, though.
The fundamental flaw in the concept lies in conservation of rotational inertia. Think about a spinning ice skater - as she draws her arms in, she spins much faster. The opposite is also true - as a rotating mass extends from its center, its rate of rotation decreases.
The space elevator rotates at a constant geosynchronous rate, but as its payload is raised along that axis, the difference between its linear inertia at the surface of the earth and its linear inertia around the circumference at geosynch altitude (or any significant altitude along that axis) is absorbed by the elevator's structure.
Unless the payload applies some sort of thrust perpendicular to the axis of the elevator, that difference in inertia only works to pull the whole system back down to earth. Effectively, the amount of energy you'd have to put into the system to keep it up would equal the thrust expended to send the payload into orbit by conventional means.
Then there's the whole issue of vibrational harmonics. Accumulated shocks from winds, payloads, and even space dust would propagate up and down the string (any human structure of that incredible length would effectively be a string in tension) and create severe vibration problems. That'd take some *seriously* epic engineering to dampen.
NASA has done some experiments with tethered satellites which address the vibration issues (as well as accumulated electric charge from atmospheric drag), but they were intended more for spinning-wheel satellite applications than for space elevators.
It's a really cool idea that unfortunately is a something-for-nothing scheme. If there were some kind of cool electric thruster system which didn't rely on reaction mass, it'd be feasable, but then we're straying into Area-51 technology.
Re:Meet George Jetson! (Score:4, Informative)
The energy required to lift a ton of cargo to GEO is the same regardless of the mechanism used (and disregarding any power you can extract from descending cargo). But there's a tremendous practical difference in that energy coming down superconducting power lines from a solar array out by the ballast or if it comes from liquified oxygen and hydrogen stored in disposable tanks. It makes a tremendous difference whether you the energy is coming via an existing infrastructure (e.g., power cables) or if if you have to waste some fuel to lift the fuel you need now.
I don't know what the current factors are, but I wouldn't be surprised if putting something into GEO requires 99 kgs of fuel for every kg of payload. A beanstalk would get you there with no "waste" other than the reusable elevator car.
As for harmonics caused by weather... I think this has been dismissed. This cable is under millions of tons of tension, and has a cross section of well under a meter when it's in the atmosphere. The load bearing core will be surrounded by a much larger infrastructure for the elevator, power cables, etc., but since it's not load bearing it can be dampened -- and is still on the order of a few meters. With such a small profile and high tension you aren't going to see much energy transferred from weather systems into the cable. (Earthquakes are another matter.)
And the conservation of momentum issues are real, but I (and others) are skipping many of the fine details for overall clarity.
Solution to those problems. (Score:4, Informative)
Then there's the whole issue of vibrational harmonics. Accumulated shocks from winds, payloads, and even space dust would propagate up and down the string (any human structure of that incredible length would effectively be a string in tension) and create severe vibration problems. That'd take some *seriously* epic engineering to dampen.
To some extent those two are each others' solutions.
The low-frequency vibration solves the pull-back problem. Thinking discretely: The weight of the payload on the thether and the taut teather form a loaded "stringed-instrument" string:
Go up a bit, you pull the string back.
Stop and wait a bit, the string accellerates you forward.
Now go up some more while the string is still going forward, providing a "pull" backward that damps the vibration, stopping the string at the vertical position.
Repeat.
In fact you do this continuously, modulating your ascent slightly so the net result is the string stays nearly vertical. When a vibration starts to build up you adjust your speed in sync to damp it.
Similarly the tether and the weight at the end (large compared to the payload) form a pendulum. It's a much more complicated pendulum than one near the surface, due to the varying gravity and the rotating coordinate system, but that's the basic idea. Again thinking discretely:
Go up a bit. The couterweight pulls back.
Stop and hang around. The counterweight starts going forward.
Go up some more. You decelerate the counterweight and bring it to a stop near the top again.
Repeat.
Again you do it continuously, this time keeping the weight at a constant displacement behind the point over the tether's base. The slant of the tether corresponds to a forward accellerating force from the rotation of the earth, providing your angular-momentum transfer by accellerating your payload and decellerating the earth. (Coming down you push the counterweight forward to accellerate the earth and decellerate the payload.)
Now there may be one or more locations along the tether where what you have to do to damp the two modes is exactly opposite. But if you've kept it damped on your way to those spots you should be through before an oscilation builds up. Or run two or more payloads simultaneously and coordinate them so you can always damp both modes. (Multiple coordinated payloads can also provide better damping and trade off each others' effects on the tether to achieve faster travel.)
Of course you have to put your counterweight a bit further above geosync, so lift losses when it is displaced downward slightly don't turn into a positive-feedback collapse.
If you don't have enough payloads in transit you can damp higher-frequency modes against the atmosphere with a few active airfoils spotted along the tether. (REALLY high frequency stuff - like seconds-to-audio - you can damp with a couple small structures attached near the geosync level.)
Effectively, the amount of energy you'd have to put into the system to keep it up would equal the thrust expended to send the payload into orbit by conventional means.
No.
The amount you have to put in is only a small delta above the amount that you would have had to put in to run an electric elevator up an idealized stiff structure of the same height - and the delta approaches zero as your damping approaches perfection.
But once it's up you don't need to power it AT ALL, which I'll get to in another posting.
Re:Meet George Jetson! (Score:2)
Re:Meet George Jetson! (Score:3, Interesting)
How does this work? Simple. After you have successfully sent so much stuff into orbit, your going to start to want to bring things back down, whether this be from mining other planets or simply getting the astronaughts back to their parents. Normally, we waste all of the energy on reentry because we don't use it for anything. With an elevator, the energy being exerted by gravity on the way down can be used to balance out the gravity being used to get other stuff up. Hence, you don't need as much energy overall to get stuff into orbit.
And as others have already stated, once out of the earth's gravity, you don't need that much energy to move around at all...
Wonka-Vator? (Score:3, Funny)
Last time this came up on /. (Score:5, Interesting)
Re:Last time this came up on /. (Score:3, Interesting)
The tram is "mega-tsuanmi". No I didn't make that up.
For a really good example of space elevators... (Score:2)
...or "beanstalks" as the insiders like to call them, read the scifi/humor novel Rainbow Mars by Niven. It features beanstalks in many places, including what happens when one pulls loose from Brazil.
OT - Fiction for this scenario (Score:4, Informative)
This disaster was used (although on Mars) in the plot of in Kim Stanley Robinson's Red Mars [amazon.com] (or maybe Green Mars... can't remember). In that case, though, the "beanstalk" was sabotaged as a weapon during a revolution. It wiped out a slice of a city, puncturing the atmosphere of a bunch of buildings, but had no casualties outside the settled areas. Can't have a tsunami in that thin an atmosphere.
Re:OT - Fiction for this scenario (Score:3, Interesting)
Re:Last time this came up on /. (Score:2)
The physics of collapse (Score:2)
Re:The physics of collapse (Score:4, Informative)
I didn't do any math for the damage caused by pieces below that mark, but my guess is that anything below a few km wouldn't be any worse than dropping a WWII bomb and the resulting damage would be very localized. between that and several thousand km, the chunks would fall into the water (assuming the builders were smart enough to build close to a coastline on the correct side:). There would be a region above those thousands of km where the chunks would be a bit more of a worry, but above that, they're likely to burn up when they hit the atmosphere.
Beyond all that, buggered if I know :)
Fire is DANGEROUS - STOP THE FIRE .... (Score:2, Troll)
You do realize we HAVE to leave earth or we die here! What, you think the Sun is going to burn forever? Long before that, we will get hammered by some multi km asteroid that will barbecue most of life here anyhow! Wake up, get your act in gear, it's time to colonize space while we still can.
The solution to this problem is also simple. Each piece needs to be aerodynamic anyhow, so add some flight control surfaces so it can "fly" apart under control...
Re:Fire is DANGEROUS - STOP THE FIRE .... (Score:2)
Re:Fire is DANGEROUS - STOP THE FIRE .... (Score:2)
Re:Last time this came up on /. (Score:2)
The real problem with a space elevator (Score:2)
Is that you could no longer have satellites in any orbit other than geosynchronous unless their orbits were very carefully tuned to avoid hitting the cable.
BTW: A space elevator will never really fall, if you put a rocket on one end you could get it to pinwheel, but I don't think any terrorists would have the time to attach a rocket motor with sufficient thrust to get it to do this.
No really, think about it, the space elevator would be rotating about GEO at exactly one rotation per day clockwise, while the earth rotates about its center at one rotation counterclockwise. Nothing you could do at the end would allow you to make the elevator fall.
If you really wanted the elevator to fall, go to the center of mass and cut it in half. That'll bring it down quickly.
BTW, read Rainbow Mars by Larry Niven, even if it is fantasy. You'll probably agree that we really don't want a space elevator :)
Re:Last time this came up on /. (Score:4, Informative)
Re:never will be safe (Score:5, Funny)
If we let that stop us, then the terrorists have already won!
Could be made safe with nanotech (Score:2)
Something like this wouldn't be built for at least 20 years from now. By then simple nanomachines should be available, since much of the construction of this would probably be done at a nanoscale. If there were swarms of nanomachines all up and down the cable and if they were made to detect any abnormalities in the structural integrity of the elevator, they could simply deconstruct it. Billions of micron length strands of bucky tubes should not have that much of an impact on the ground due to friction in the atmosphere. It would simply be dust particles floating around. I'd think the deconstruction of the cable could be done in a relatively short amount of time as well. The only problem with this would be false alarms, but then again with that kind of technology it wouldn't take too long to reconstruct a new cable.
Just some thought anyway..
Re:never will be safe (Score:2)
I don't have any idea what would happen if it broke free while mostly intact, but we could always make sure it breaks up in that case. If nothing else, the defense force could just shoot at it.
I think those few ships would probably just be a few missle cruisers in a ring. If there is no legitimate air traffic in that area, they have a lot more leeway to defend the elevator. Anyway, it's not like Aegis cruisers have never shot down airliners before... (U.S.S. Vincennes, late 80's)
Re:never will be safe (Score:2)
Re:never will be safe (Score:2)
Translation: "I can't imagine any solutions for these problems, therefore no solution could possibly exist".
SF Books (Score:2, Informative)
Read Fountains of Paradise (Arthur C Clarke)
It's all explained in those books.
Charles Sheffield (Score:2)
(The fact that the short story was so thin was because the concept was still so new - he had to spend most of the story answering the questions the reader would be invariably asking. And satisfying the unique political... orientation... of that Baen "book-zine" publication.)
Unfortunately I can't remember the name of either now, or even the name of the book-zine.
Caveats (Score:5, Funny)
a /. favorite (Score:2, Redundant)
Re:a /. favorite (Score:3, Insightful)
--
Evan
Re:a /. favorite (Score:2)
Other than the fact that the report has been rewritten, doubled in size, and links out to new reports?
Ever heard of a living document, Marc?
--
Evan
Re:a /. favorite (Score:2, Funny)
Is that like the free book of mormon [mormon.org]?
Re:a /. favorite (Score:5, Funny)
Lucky for me, I love Space News.
see what happens when one of these break... (Score:4, Offtopic)
Re:see what happens when one of these break... (Score:2)
Does this cable conduct electricity? (Score:2, Interesting)
Re:Does this cable conduct electricity? (Score:2, Informative)
A carbon nano-tube cable shouldn't develop any electrical potential moving through a magnetic field. This might be a problem with any metallic cabling run along the support cable for data transmission purposes, but I really doubt they'd want to do that. Added weight and all. On the other hand, it's free power.
Wind would probably be a very minor issue - compared to supporting it's own weight, wind would provide a fairly minor amount of stress. Static electricity - Maybe just run a ground up and down to deal with that a lightning.
Why beanstalks won't happen here. (Score:3, Interesting)
On the moon, Mars, any other sparsely-populated/unpopulated body in the solar system? Sure. But not here.
Re:Why beanstalks won't happen here. (Score:2)
Now you just have to worry about Green Peace.
Re:Why beanstalks won't happen here. (Score:2)
Now you just have to worry about Green Peace.
You know what a little earthquake can do to a shoreline thousands of miles away? If it fell out of the sky in the Pacific, it would take care of JavaOne this year....
Re:Why beanstalks won't happen here. (Score:2)
Barring safety issues as mentioned by the previous poster, I would think Greenpeace would be all for this. It would replace rocket launches, many of which are quite environmentally unfriendly. The environmental effects of a space elevator, on the other hand? Negligible, as far as I can tell.
Re:Why beanstalks won't happen here. (Score:2)
It will have to be near the equator (geosync) for this thing to work.
Sure sounds crazy, but this sounds awfully cool
Atomic Train (NBC) (Score:2)
A train containing an atomic (not thermonuclear) bomb crashes in the mountains 40 miles west of Denver. It detonates! What would I do?
I told my mom I would go outside to watch. An atomic detonation at 40 miles away doesn't bother me. An accident at Rocky Flats (5 miles south) when it was operational is a bit worrisome, but not a fission explosion 40 miles away with several mountain ranges between us. Even a thermonuclear explosion at that range is not the instant death portrayed in that movie.
The point is that nuclear weapons, as destructive as they are, are still largely local events. The cable smacking into the equatorial oceans would dump a lot of energy into the water, but that energy would be spread across coastlines worldwide. Millions may still die, but not billions. And that risk may well be considered acceptable if the alternatives are far worse.
Re:Why beanstalks won't happen here. (Score:2, Informative)
If it *does* fall down it won't case all that much damage. The cable will wrap around the earth in a straight line from where it was cut. At the beginning of the impact the kinetic energy wouldn't be that much it wouldn't be until later on that you would have to worry about any serious affect. By the second time around the earth the cable will began deterioting and exploding in the upper atmosphere.
Also since this has top be placed in a geo-synch orbit it needs to be located close to the equator. I.E. if it falls it hits a whole lotta ocean and not much else. It shouldn't be too hard to figure out a spot where it nearly completely avoids populated areas. Futhermore having breakaway points on the cable itself would allow for only say 1/10 of the cable to impact the earth the rest would break and fly off into space. place it on the coast, the thing breaks off and the 1/10 impacts the pacific/atlantic ocean. Done deal.
If we can build a damm space elevator we can protect it!
Re:Why beanstalks won't happen here. (Score:2)
Yeah! Tough shit for those annoying countries
at the northern part of S. America. And Africa, don't get me
started on Africa. Serves them right if a high-speed cable comes
crashing down across the widest part of the African continent
twice! They're lame...and so's all the African wildlife!
Anyway, they ain't rich and powerful so screw 'em. YES in
your backyard!
It's a moot point anyway. One wont be built anymore than
an Orion will.
Re:Why beanstalks won't happen here. (Score:4, Informative)
Essentially, orbit means "centripetal force juuuust matches gravity." If the top is in geostationary orbit, then only the top is in microgravity. Every single inch below the top has a net force pulling downward. The lower your altitude, the faster you have to go to be in orbit (one revolution per day at geostationary, one revolution per hour at LEO). A break at any point in the beanstalk would bring it down.
You could make it tall enough so that the sum of the centripetal force of the end counterbalances the weight of the structure, and this would put the structure under tension instead of compression.
However, if you cut the structure anywhere between the surface of the earth and geostationary, everything below the cut will come crashing down. Fly a plane into it at seven miles, and you have a seven mile structure (about 35 times the height of the WTC) falling towards you. If the US can hit ballistic targets at a few hundred miles up with a kinetic-kill vehicle, Joe Shmoe with his suitcase nuke on a V-2 can hit a stationary target at that altitude. If there's a time-bomb on the elevator that goes off when the elevator floor is at or near geostationary, then we have 22,000 miles of material coming down.
"And the cable itself can withstand the force of multiple nuclear explosions (has to b/c of forces acting upon it)meaning it ain't coming down easy."
Tension, compression, and shear are three different things. Just because a material can withstand one or two of the three doesn't mean it can withstand all three.
And then there's a fourth factor: Heat. This was the WTC's weakness. While the steel structure withstood the airplane impacts, it couldn't survive the heat of the fire. Sure, the beanstalk might be able to survive the blast from a nuke, maybe even a shockwave if it was within the atmosphere, but nothing can survive the heat.
"The cable will wrap around the earth in a straight line from where it was cut."
No. Your main problem here is that you're assuming that all the mass will be at the top of the structure, forcing the structure below it to follow the top along as it comes down. Gravity being what it is, the center of gravity (assuming a structure of uniform density) will be somewhere between the bottom and the half-way point. And because gravity increases exponentially as you go down, taller structures will have their centers of gravity further from the midpoint than shorter ones.
So while you're correct in thinking that each unit length of cable will have to deal with tension in the cable (due to the motion of the rest of the cable) as well as gravity, you're incorrect in guessing what direction that tension will pull. For points in the structure higher than the center of gravity, the tension in the structure will be the stronger of the two forces, pulling the structure down along it's length instead of letting it spiral down in free-fall.
If anything, the top of the structure may fall along a straight line because it got snapped like the end of a whip, giving it more kinetic energy than it would have had if it were just in free-fall (and causing more damage than a free-fall would have done).
"By the second time around the earth the cable will began deterioting and exploding in the upper atmosphere."
First off, you have no idea how large these pieces may be when they break off. Second, all the kinetic energy of hundreds or thousands of miles worth of stuff has to go somewhere. If the actual mass doesn't make it past the upper atmosphere, then the momentum and kinetic energy just gets transferred to the atmosphere, which means a shockwave.
"Also since this has top be placed in a geo-synch orbit it needs to be located close to the equator. I.E. if it falls it hits a whole lotta ocean and not much else."
Tsunamis. Big tsunamis. And most of the world's population lives within 200 miles of the ocean.
Remember, something with the mass of a small island killed off the dinosaurs. What we're talking about is a structure with at least that much mass. While it may not be one big chunk, mass is mass and it's still coming down in a very short period of time.
"Futhermore having breakaway points on the cable itself would allow for only say 1/10 of the cable to impact the earth the rest would break and fly off into space."
Just for the sake of repeating myself, if the cut is anywhere between 0 and 22,000 miles up, anything below it is coming down. Period.
AC Clarke's Fountains of Paradise (Score:2, Informative)
Where's the info on the counterweight? (Score:3, Interesting)
Re:Where's the info on the counterweight? (Score:2)
But even if you lift it from the ground you can still bootstrap the system. Say the cable extends an extra 20k past GEO - maybe you start with a minimal core and skimpy cars and can only lift 50 extra pounds. No problem, you just lift 50 pounds at a time for a few months. Then 100 pounds at a time. Then 200 pounds. Over time you can expand the core, improve the cars, and continue lifting additional mass into the ballast.
Re:Where's the info on the counterweight? (Score:5, Insightful)
Re:Where's the info on the counterweight? (Score:3, Informative)
Re:Where's the info on the counterweight? (Score:3, Interesting)
No, not the center of mass but the center of gravity, which when you're talking about structures this high is a completely different animal. Because the force of gravity drops off exponentially with altitude, the bottom is always heavier than the top and so you'll need to put more on top to get that center of gravity higher.
I did the math last night with the help of my TI-92. Assuming a structure of uniform density, to put the center of gravity of the structure at geostationary altitudes (about 22,000 miles or 6 earth radii) requires the entire structure to be about 985 earth radii (about 20 light-seconds) tall.
With a structure that high, people at the top would experience a net acceleration of about 3 g's outwards and be travelling at about 960,000 miles an hour.
Of course, this is all moot because it would only stand for a few weeks until the moon breaks most of it off at 60 earth radii.
Re:Where's the info on the counterweight? (Score:3, Insightful)
It doesn't drop off exponentially, it drops off as the inverse square. This is an awful lot different from exponential. The universe would be much different if the force of gravity was proportional to e^(-r) ;)
hold up... (Score:5, Funny)
Grrrr
Re:hold up... (Score:5, Funny)
Okay,. who did that?! (Score:5, Funny)
here's a (slow) link in html format (Score:3, Informative)
Damn! (Score:4, Funny)
Pie closer to hand (Score:5, Interesting)
There are some variations on the idea though,like this one [imm.org], that are close to being possible with today's technology, and can even be provisionally costed. Basically the idea is to construct an elevated runway about 100km up, and use mass drivers to hurl stuff into orbit. At that altitude the saving from air resistance is huge and mass drivers become very efficient
At this stage, NASA speanding serious time thinking about space elevators is probably no more useful than daydreaming. Thinking about this kind of thing is probably more productiove though, becuase something might come of it in the medium term, and its almost as efficient as an evelator anyway - with the decided advantage of not being able to collapse and strangle the planet.
(Since I heard about this from a NASA researcher, maybe Im being a little harsh to accuse them of daydreaming)
Why, when I was your age....! (Score:5, Informative)
The numbers were so ludicrious that he repeatedly apologized for wasting our time. Of course this was a flight of fancy, the numbers were orders of magnitude larger than the strongest known materials. Yet, if "ultronium" could be developed from some exotic material....
Then buckyballs were discovered. Then buckytubes.
The fact that this is even "just" possible with known materials less than 20 years later is mindblowing. I can only compare it to the confident RSA predictions in Scientific American (which I also remember when it first appeared) that RSA-128 would take millions of years to crack. We all know how well that prediction held up.
Given this perspective, I don't think it's unreasonable for NASA to spend some serious money considering its options if/when stronger materials become available. It's easier to believe that even stronger materials will be discovered (e.g., perhaps by putting foreign elements within the tubes to manipulate quantum properties) than that we've suddenly hit the ultimate barrier.
Only 20 tons? (Score:4, Insightful)
Re:Only 20 tons? (Score:2)
Re:Only 20 tons? (Score:2)
Re:Only 20 tons? (Score:2)
Besides, if you build one, you can build one for other governments, cheaper than they can build one themself. So you can defray your costs by making money that way.
Playing Devil's [Luddite's] Advocate (Score:2)
Saving some cable... (Score:2, Interesting)
I've read several books which include the idea of a space elevator, and one of the key problems had to do with bringing that much cable to space, and the strength of the cable to stay together. The closer the cable gets to earth the harder the pull, the further out the "satellite" holding the cable in geo-synchronous orbit has to be. Instead of bringing the cable down to earth.. or putting it atop a very high tower, why not create a platform 50-80,000 feet up for planes to land on. This would save very large amounts of cable from being created, the satellite wouldn't have to be nearly as far out either to compensate for the gravitational pull from the cable below. Also, to compensate for the excess weight of the aircraft and payload while landing, the satellite holding the cable could move up and down to balance any weight added or removed to the cable.
Now, having a shortend cable would have added benefits too, in the event of a disaster, normally a cable attached to the earth would wrap around the planet several times causing an incredible amount of destruction. This could be minimized with my platform idea. Imagine something colliding with the cable causing immenant failure... why not create sections in the cable to automatically break off in the event of a disaster, this would minimize the amount of cable falling to earth, and the remaining cable would be either ejected into space, or depending on how an object hit, its possible the upper section could re-establish a geo-syncronous orbit after losing much of the cable.
Any pysicists out there able to agree/disagree with this? The tether would also most likely have to be conical in shape, thicker higher up, and thinner below to minimize the amount of carbon tubing used in the elevator.
Re:Saving some cable... (Score:3, Insightful)
Thats a good idea, but... How do you purpose to keep the platform suspended? Is it hanging "off" the satelite? If so, won't its weight drag the satelite into a lower orbit, eventually destroying it? Or is the satelite going to be continuously firing retro-rockets, which would need enormous amounts of fuel, thereby negating the purpose of the elevator? Not to mention the wind blowing said platform around.
Re:Saving some cable... (Score:2)
Re:Saving some cable... (Score:2, Interesting)
This Won't work - They forgot the taper factor (Score:5, Interesting)
The deployment method they're using doesn't take account of the fact that you need the thickest part to always be at the middle - if you simply unroll it the way they suggest then the incorrect thickness profile will result in the cable exceeding it's breaking point and snapping.
What they need to do is unfurl a cable like this from geostationary orbit simultaneously up and down at the same time. The Mechanism to do this would have to be very delicate at unfurling the last kink or the cable will again snap.
The cool thing about this is if you figure out what kind of weight you want the cable to support then you can come up with an idea of the amount of energy stored in the tension. If the cable snapped at any point then the amount of energy released would be pretty phenomenal. From each end of the snap you'd generate a compression wave which would get stronger as it travelled along the cable, after a while of picking up energy it may turn into a shockwave and snap the cable again (essentially shattering the cable). If it doesn't then the wave will have energy equivalent to nuclear weapons when it reaches the endpoints and the waves transmit themselves into the supporting structure....
Bubblegum Crisis 2040 (Score:3, Interesting)
MP3 Interview... (Score:2)
SciFi comes through again... (Score:4, Informative)
Cell phones
Internet
Submarines
Man on the moon
Hyposprays (Yes, really)
Skyscapers
Television
And many many more. Try using that list next time someone says that scifi will never come true. It'll quiet them down real fast.
Fun things to try (Score:3, Funny)
Hacking the Space Elevator "this is the down signal"
Getting Greenpeace to fly a very large flag from the Space Elevator "better than a smokestack"
Getting a bunch of friends to ride up with you and all sway together so it rocks
Tossing pennies over the railings and watching them burn up on reentry
Paragliding from the space elevator
Paragliding onto the space elevator (not for the faint of heart)
Downloading images from the Space Elevator Coffee Pot webcam
Taking a dump - has to go somewhere
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Stuck between floors? (Score:2, Funny)
Never happen (Score:2, Insightful)
An article about this from August 1979 (Score:4, Interesting)
"Beanstalks, originally called skyhooks, are an idea of the 1960's whose time may at last have come. They are used as important elements of at least two novels published in 1979, Authur Clarke's 'The Fountains of Paradise' and my own 'The Web Between Two Worlds' "
Nope, doesn't work (yet) (Score:4, Informative)
OTOH, single fibers are almost strong enough, but only if you allow absolutely no 'safety factor'. Most normal engineering uses atleast 2 safety factor, and usually many times that. But as nobody knows how to splice them together into a rope, and doing so would lose atleast 25% strength, it's not enough.
He's got the best architecture I've seen for this by a long way, nice paper study. Not practical right now. Hope somebody sorts out the fibers very soon.
Re:Nope, doesn't work (yet) (Score:4, Informative)
Carbon nano-tubes have a strength to weight ratio that is roughly 100x that of kevlar, and depending on how it's rolled can be either an insulator, a smiconductor, or a conductor.. Pretty cool stuff.. Unfortunately, they can currently only be manufactured in micron lengths..
Technology of Indian Snake Charming (Score:3, Funny)
Is this article a troll? (Score:3, Funny)
NASA began considering the concept in June 1999 at the Advanced Space Infrastructure Workshop on "Geostationary Orbiting Tether 'Space Elevator' Concepts" held at the Marshall Space Flight Center in Huntsville, Alabama.
GOTSEC? Can this be real?
"Ring" construction (Score:4, Interesting)
Basically you launch your cable fabrication facility and create a *huge* loop of cable. Something long enough to encircle the earth at geostationary orbit. This loop is initially unstable and will require temporary station keeping engines. You don't care about north-south twists, but don't want in-out twists to grow to large. (Read any analysis of _Ringworld_ for details...)
You then turn the cable machines on their side and start laying cable towards/away from earth. The cables will follow local geopotential fields down and up, and eventually you'll have a starter cable touch down. This can be a temporary cable, designed to be discarded, that does nothing but throw mass up the cable to build the ballast and feed additional cable machines that are producing the production cables.
Eventually you have ring in geostationary orbit, plus numerous anchors along the equator. You supplement the ring at geostationary orbit with another ring a bit inside (or outside) of it so that it's always under tension.
Besides solving some construction issues, it eliminates many of the collapse modes. If the cable snaps, the upper portion is kept in place by the ring. Even if all cables are snapped, the ballast weights will keep the ring under tension and survivors can manage station keeping by dumping ballast. (Unfortunately, if all cables snap the rest of the system will have a different net orbital velocity and there could be a big jolt.) Since there are multiple anchors, there's little value to terrorists in destroying any single anchor.
I know that _3001_ mentioned a ring as an endstage after building the first beanstalk, but I thought I've seen papers suggesting they be used as a construction platform.
And the secondary benefits are huge. Let's say the ring is 250,000 km long, and there's a 500m wide band of solar cells attached to that ring. The solar constant is around 1370W/m^2, that's potentially 171 GW of pollution-free power than can be fed down superconducting cables - 540 trillion kWh/year. According to the USGS the US consumed about 9 billion kWh/year of power from all sources in 1998, so even if the ring has only 1% efficiency it would still provide every person in the world 300x more power than the average American consumed in 1998!
Re:I wonder if trips to space would be cheep? (Score:5, Informative)
To transport you (70 kg) up to an altitude of 200 km would take roughly 140,000 kilojoules of energy (you do the math ... first year physics stuff). However, they can't just lift you, they also have to lift a vehicle containing you. Say the vehicle weighs 500 kg for every person it can carry -- this would take rougly 1,000,000 kilojoules. If they do this electrically (which is one of the more expensive forms of energy), at 100% efficiency it would eat up roughly 300 kWh of energy. At 0.30/kWh (say), that's roughly $100.
Of course, a clever engineer would realize that every vehicle going up eventually goes down ... so the vehicle on the way down could be used as a generator, feeding power to the load of a vehicle going up. Equally obviously, we're not considering the amortization of the construction cost, which would be monumental.
Re:I wonder if trips to space would be cheep? (Score:3, Informative)
You would not stop at the 200km height, no more than you get off a ski lift at the first tower.
At the 200km height another poster mentioned - you would have a hard time finding any change in your weight. Instead of being something like 6400 km from the center of the earth you're 6600 km away. That's enough for about a 6% change - less than the annual weight change by many people on yo-yo diets.
Re:I wonder if trips to space would be cheep? (Score:2)
Correction... (Score:2)
Re:I wonder if trips to space would be cheep? (Score:3, Interesting)
If you are below the geosyncronous orbit you'd feel slight gravitational pull and above it you'd feel the effect of sentripetal force of the elevator keeping you attached to the earth - you'd actually be standing on the roof then.
Shuttles are normally orbiting the earth at a speed and height (mv^2/r=GmM/r^2) where earths pull is just enough to keep them on a steady circular course around earth - so they are technically free falling but never approaching earth. Geosyncronous orbit is just a special case where you're going at the same angular velocity as earth.
Yes. Re:Rotational energy (Score:5, Interesting)
Physics works everywhere all the time. When you climb a flight of stairs or walk up a hill it slows the Earth's rotation - and it speeds back up as you walk back down.
No - seriously - just as an ice skater's rotation slows or speeds as they extend or contract their arms the same principles apply to all rotating bodies. Everytime we slingshot a space vehicle around the Earth we are effectively transfering some of the planet's energy to the vehicle and that energy has to come from somewhere.
But the amounts here are so small that the effect is not measurable or "effective" in the scale of anything we could notice. It's like the fact that anything with mass has a gravatational field - but you don't notice the effect of the gravity created by your pen.
=tkk
Re:Yes. Re:Rotational energy (Score:3, Informative)
A sakters arems and body have the same angular velocity, because her arms are attached to her body. it takes more energy to move her arms around when they are extended (further to go) and since they are attached to her body, the whole thing slows down.
In a space ship, the earth and the ship are not attached. As soon as the ship leaves the ground, the earth spins out from underneath it. Due to momentum, and air viscosity (pushing the ship in the direction of the earths rotation) this is not nocieable until the ship is quite high, but conservation of rotational inertia is not the principle you need to follow in this case.
Dams *have* changed length of earth's days (Score:3, Interesting)
(The main reason the earth is slowing down, IIRC, is the tidal forces from the moon and sun. If the moon was gravitationally bound to the earth it would be falling, but since it's not it's slowly drifting away.)
Re:Could you imagine... Yes, I can! (Score:2)
On the way to the sun first should be:
1. The source code and any disks containing Windows 3.11 and Win32s. Puh-leeeez! Pretty Puh-leeeeze!
2. All the AOL CDs on the planet - though that would break the damned thing, wouldn't it?
3. Hillary Rosen. (Just an elevator ride, Hil! Really!)
4. The Microsoft Marketing Department. They've made the rest of the industry go to hell, so....
5. Larry Elliston's ego. Might make the Sun go nova, so we'll have to do some calculations first.
6. Ditto for BillG, SMcNealy and SJobs.
7. All e-mail SPAM. The Internet's equivelent of nuclear waste.
8. Jon Katz stories and Cowboy Neal polls.
Did I forget everything, er, anything?
Soko
Re:Could you imagine... Yes, I can! (Score:2)
Re:Just a pie-in-the-sky idea (Score:5, Interesting)
The semiconductor industry figured out how to make large single crystals of ultra-pure silicon, then pattern the surface down to a ridiculously fine resolution. The fiberoptic folks figured out how to make glass so clear that a light pulse can go through many many miles of it and still be recognizable at the other end. Molecular biologists can "amplify" single molecules of DNA into macroscopic quantities.
I wouldn't be so quick to say that we will never be able to make carbon nanotubes that are long enough to be useful as structural materials.
Re:4 problems I see with the idea... (Score:2, Funny)
The other end is in orbit, it can easily move nearer or further the earth