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Space Science

Future of Space Elevator Looks Shaky 486

lurking_giant writes "In a report on, 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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Future of Space Elevator Looks Shaky

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  • Told you so (Score:5, Funny)

    by Junior J. Junior III ( 192702 ) on Tuesday December 09, 2008 @02:45PM (#26049381) Homepage

    I told everyone it wouldn't work. But would they laugh at me? No!

    • Re:Told you so (Score:5, Interesting)

      by pitchpipe ( 708843 ) on Tuesday December 09, 2008 @03:14PM (#26049785)
      Seems Charles Stross has it about right, from his book "Saturns Children" [] p. 113:

      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.

    • Re: (Score:3, Interesting)

      by Anonymous Coward

      Very amusing indeed.

      Especially since Kim Stanley Robinson wrote his "Red Mars" series & specifically addressed these issues. He correctly identified the problems, and came up with very realistic solutions.

      Yes, the orbital section had to have thrusters to combat what is mentioned in the article.

      He also determined that the 'elevator' portion would require significant advances in materials, and require a futuristic substance that could withstand the sheer loads & twisting due to wind, atmosphere, etc.


    • Re:Told you so (Score:5, Interesting)

      by causality ( 777677 ) on Tuesday December 09, 2008 @04:32PM (#26050927)

      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.

      • Re:Told you so (Score:5, Interesting)

        by Nefarious Wheel ( 628136 ) on Tuesday December 09, 2008 @05:12PM (#26051531) Journal

        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.

  • by JCSoRocks ( 1142053 ) on Tuesday December 09, 2008 @02:45PM (#26049385)
    Willy Wonka had it right. We should just be doing that instead.
  • by Anonymous Coward on Tuesday December 09, 2008 @02:47PM (#26049407)

    If an elevator won't work what about a space escalator?

    • by JCSoRocks ( 1142053 ) on Tuesday December 09, 2008 @03:01PM (#26049607)
      Why take the escalator when I can take the stairs? *steps down behind couch*
    • Re: (Score:2, Funny)

      by jbeaupre ( 752124 )
      With my luck, I'd get halfway up the space escalator and drop my luggage. It would thump its way down to with me running after it. It was embarrassing enough at the Aukland airport having everyone watch me put on a show, but to have it happen in front of half a continent, argh!
    • But how in the hell are they going to make it comply with the ADA? 8^)
    • Serious Alterantives (Score:5, Informative)

      by MozeeToby ( 1163751 ) on Tuesday December 09, 2008 @03:20PM (#26049859)

      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 ( []).

      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.

      • Re: (Score:3, Informative)

        by liquidpele ( 663430 )
        For future reference, Wikipedia does not like the slash at the end of links.
      • Corrected Link (Score:3, Informative)

        by lowy ( 91366 )
    • by tmosley ( 996283 ) on Tuesday December 09, 2008 @04:32PM (#26050901)
      ..a space escalator can never break, it can only become space stairs.
  • by brian0918 ( 638904 ) <(moc.liamg) (ta) (8190nairb)> on Tuesday December 09, 2008 @02:48PM (#26049419)
    There's also the problem that any ninja can come along and cut the cord, and suddenly you have a $500M paperweight wrapping around the earth tearing a path of destruction.
    • Ahhh.... I see you've read the Red Mars trilogy where exactly that happened (albeit on Mars not the Earth.)

      I always thought the space elevator seemed impractical. First there's a LOT of material needed to create the cable. Than there's the problem of "lowering" that massive cable to the ground. And of course it's vulnerability to shifting; half the time we can't even keep our satellites in the sky - how could we guarantee a cable would stay there?

      Like "warp speed" it's a neat scifi idea, but not going t

      • Re: (Score:3, Insightful)

        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.


        Than there's the problem of "lowering" that massive cable to the ground.

        Actually, I think the idea is that cars would run up and down the cable -- even as simple as, the cable stays put, and the cars use motorized wheels.

        And of course it's vulnerability to shifting; half the time we can't even keep our satellites in the sky - how could we guarantee a cable would stay there?

        Well, the base would be mobile too -- in the ocean. But I see your point.

        Like "warp speed" it's a neat scifi idea, but not going to happen within our lifetime.

        No, unlike "warp speed", it's actually not make-believe, and very likely not impossible. It just might turn out to be impractical, or not worth it.

        That is: We know roughly how we would bu

        • by steveo777 ( 183629 ) on Tuesday December 09, 2008 @04:00PM (#26050461) Homepage Journal

          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!

  • Scary stuff (Score:5, Interesting)

    by glaswegian ( 803339 ) * on Tuesday December 09, 2008 @02:49PM (#26049425)
    The engineering required for this elevator is mind boggling. After witnessing the amount of time and effort that went into a small suspension bridge spanning the river Thames in London (The Millenium Bridge []), the mere idea of this elevator scares the shit out of me.
    • Why does it scare you? Because it isn't easy? Just because it's difficult, doesn't mean you should be scared.

      • by IceCreamGuy ( 904648 ) on Tuesday December 09, 2008 @02:57PM (#26049547) Homepage
        you will be... you... will... be...
      • Re:Scary stuff (Score:5, Insightful)

        by glaswegian ( 803339 ) * on Tuesday December 09, 2008 @03:01PM (#26049609)
        I'm not saying it shouldn't be done. I guess my point is that the Millenium Bridge is so simple by comparison, yet it needed ~2 years of repairs after opening because of a wobble. People could have been thrown into the Thames, but no big deal, I guess. The space elevator, however, seems so much more prone to failure and with much bigger consequences.
      • Re: (Score:3, Insightful)

        by 54mc ( 897170 )

        We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.

    • by zmollusc ( 763634 ) on Tuesday December 09, 2008 @03:08PM (#26049715)

      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.

    • The engineering that was required for the Apollo missions was mind-boggling too, especially when you consider they were using computers back then less powerful than a typical scientific calculator, and didn't have much of our advanced materials science. Regardless, they managed to send people to the Moon many times, without any loss of life, and only one incident (13) which didn't result in any casualties.

  • by Cyberax ( 705495 ) on Tuesday December 09, 2008 @02:50PM (#26049439)

    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.

    • Why not compensate for Coriolis force by using rockets?

      I see you made it through two sentences in the summary. How about trying to read the third? "All of this would likely make it necessary to add thrusters, which would consume fuel and negate the benefits of the concept."
      • by Cyberax ( 705495 )

        There's a difference - Coriolis-negating thrusters need not to have high power. We can use small effective ion engines with high ISP. They can't be used for launching rockets from the Earth.

        It might be possible to save more general capacity by using small thrusters. I'm trying to calculate it right now.

        • Re: (Score:3, Funny)

          by Rayban ( 13436 ) *

          Easy fix:

          Build the elevator in the Florida everglades and use mosquito carcasses as reaction mass.

  • I call bullshit! (Score:3, Informative)

    by girlintraining ( 1395911 ) on Tuesday December 09, 2008 @02:51PM (#26049459)

    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.

    • by Yetihehe ( 971185 ) on Tuesday December 09, 2008 @02:58PM (#26049569)

      The coriolis effect is not a real force. It's an illusionary effect that happens when you have a moving point of reference.

      Obligatory xkcd reference: []

    • Re:I call bullshit! (Score:5, Informative)

      by khendron ( 225184 ) on Tuesday December 09, 2008 @03:04PM (#26049645) Homepage

      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.

    • It doesn't really matter if it's a "real" force or not, the effect exists.

      If you're sitting at your desk, and someone asks if you're moving, what's your answer, yes or no? If you say no, they'll agree with you, but you'll be wrong, because in reality you're moving as the Earth's surface spins in orbit, and you're moving even more since the Earth is orbiting the Sun, and then there's movement from the solar system moving through the galaxy. But if you bring this up in conversation, people will just think y

    • "The coriolis effect is not a real force."

      You are correct only in a narrow technical sense that you clearly do not actually understand. The difference between that and being wrong is a bit philosophical for me.

      The coriolis effect is not a "force" in the clasical Newtonian definition. The coriolis effect is a real effect, that will cause real problems for anyone trying to build a real space elevator.
  • Bah (Score:3, Funny)

    by Verteiron ( 224042 ) on Tuesday December 09, 2008 @02:52PM (#26049485) Homepage

    No one said it would be easy.

    • Re:Bah (Score:4, Insightful)

      by Cadallin ( 863437 ) on Tuesday December 09, 2008 @03:15PM (#26049803)
      Damn Straight! This kind of instability is something that has been found and defeated many times before, particularly in Aerospace.

      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.

      • Re: (Score:3, Insightful)

        by geekoid ( 135745 )

        Just because some problem have been solved doesn't mean all problems are solvable.

  • by KlaymenDK ( 713149 ) on Tuesday December 09, 2008 @02:52PM (#26049487) Journal

    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.

    • by MadCow42 ( 243108 ) on Tuesday December 09, 2008 @02:59PM (#26049585) Homepage

      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.


      • My understanding is that Ion drives also need a ton of time, as their acceleration is like a giant curve. It would not be suitable for countering things in anywhere near real time.

        IE, a probe might take a month to get to the moon, but only 2 months to get to mars, etc.. (I know, my numbers are way, way off)

  • by Anonymous Coward on Tuesday December 09, 2008 @02:57PM (#26049553)

    ...,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)

    by Gr8Apes ( 679165 ) on Tuesday December 09, 2008 @02:57PM (#26049557)

    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)

    by skgrey ( 1412883 ) on Tuesday December 09, 2008 @02:58PM (#26049565)
    If all goes to hell, just jump in the elevator right before it hits the ground. Problem solved.
    • If all goes to hell, just jump in the elevator right before it hits the ground. Problem solved.

      Don't be ridiculous. It's obvious that you would want to jump out of the elevator at the last second.

  • by magsk ( 1316183 ) on Tuesday December 09, 2008 @02:58PM (#26049575)
    When it came down to it the space elevator though nice, is a dumb idea. Like the jet pack. Think if the resources needed to defend it from terrorists, or maintenance costs. Seemed also like a put all your eggs in one basket as well I mean we would be much better off to just improve our propulsion ability. Personally i like a rocket powered mag-lev launch vehicle, that would travel down a rail that ends up pointing to the sky.
    • by TheMeuge ( 645043 ) on Tuesday December 09, 2008 @03:09PM (#26049733)

      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.

    • Re: (Score:3, Insightful)

      Just the opposite, actually. The jet pack is closer to what we're doing with space right now, which is strapping huge rockets on a much smaller payload. The space elevator would allow us to use whatever energy source we want to use to get the payload into space (still a significant amount of energy). In addition, it would provide a possible electrical line for electricity to go from space to the earth.

      Arguing about protecting it from terrorists is, in a word, retarded. There's no reason that it will be a
  • by ceoyoyo ( 59147 ) on Tuesday December 09, 2008 @03:04PM (#26049635)

    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.

    • Re: (Score:2, Interesting)

      by Cormacus ( 976625 )
      I agree with your assessment of their stated problem, but I'd like to know where they got that idea in the first place. Launching directly from the space elevator has never (in my understanding) been part of the concept. Instead, cargo (+ people) is offloaded at a station and is moved into a shuttle. The shuttle detaches from the station and then applies a thrust vector to move away.

      The point of a space elevator is not to launch items directly into space, but to create a more efficient, higher through-p
  • No fly zone (Score:3, Interesting)

    by Adrian Lopez ( 2615 ) on Tuesday December 09, 2008 @03:04PM (#26049653) Homepage

    I wonder how large a no-fly zone would be required for a space elevator? After all, just imagine the damage it might cause if the thing were to collapse and land over a populated area.

    • Re: (Score:3, Insightful)

      just imagine the damage it might cause if the thing were to collapse and land over a populated area.

      Depends on how you build it. If you're using carbon nano-tubes, then not much at all. Basically, much of it would go into space, a lot would get burned up on the way down, and the rest would be light enough that it's be more like a bunch of paper floating to the ground instead of a giant steel structure falling down. If it's heavy enough to cause damage, it's probably not going to be a good material to make the elevator out of in the first place.

    • Re: (Score:3, Interesting)

      by feyhunde ( 700477 )
      Well, first you have to remember that if it fell, it would only have the part below the cut fall. So an airplane at 25,000 would cause only about 25,000 feet to fall. It's like spinning a bucket on a rope. Cutting the Rope causes the bucket to fly out. Depending on the tension on the cable we might have trouble fixing the far end, but the massive counter weight could be fixed. So a 5 mile no flyzone would work just fine. Then I gotta bring up how you want this at a low latitude with lots of shipping. Dep
  • All they have to do is redesign the car/platform/etc a little bit to compensate.

    And a small rocket would be a very small rocket, actually. we're talking hardly any more powerful than a few model rocket engines to counteract these forces.(think small thrusters or a tiny jet engine)

    It's doable. Just not as easily as we once thought.

  • 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.

    • Re: (Score:3, Funny)

      by Chris Burke ( 6130 )

      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.

      I know what you mean. Turns out it was steak knives. Anti-climactic for sure.

  • by Anonymous Coward

    OK... what if we built this large wooden ladder...

  • by jandrese ( 485 ) <> on Tuesday December 09, 2008 @03:11PM (#26049755) Homepage Journal
    Of all of the technical and political roadblocks to building a space elevator, both of these seem quite minor in comparison. This is kind of like saying "I was going to bench press this Hummer H2, but since you added a fuzzy steering wheel cover it's going to be completely impossible now."
  • Of course (Score:4, Funny)

    by Strange Ranger ( 454494 ) on Tuesday December 09, 2008 @03:12PM (#26049761)
    This idea has it's ups and downs.
  • by w0mprat ( 1317953 ) on Tuesday December 09, 2008 @03:28PM (#26049957)
    Corrolis force problems were one of the first things I thought of when I first heard about the space elevator, but I'd never seen the issue brought up.

    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...
    • Re: (Score:3, Informative)

      by diablovision ( 83618 )

      It's accelerated by the tension of the space elevator cable, which is attached to a large counterweight beyond geo-synch orbit. This causes the elevator cable to pull on the counterweight and on the Earth. Eventually the orbital energy comes from the rotation of the Earth, slowing it ever so slightly. The system naturally returns to a state where the elevator cable is perpendicular to the plane tangent to the earth's surface at the attachment point as the counterweight drifts back into a higher orbit via c

  • by monk ( 1958 ) on Tuesday December 09, 2008 @03:39PM (#26050091) Homepage

    A rotating skyhook (a rotating line connected to a ballast on one end and a payload on the other) wouldn't have that problem. []

    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.

  • by sean.peters ( 568334 ) on Tuesday December 09, 2008 @03:52PM (#26050305) Homepage

    Coriolis force as a show stopper? Well, given that:

    • current nano-fiber technology has to improve by a couple orders of magnitude before we can even think about building such a cable
    • the costs for building the cable aren't even possible to estimate, and are likely to dwarf the cost of conventional rocket launch for the foreseeable future
    • the technology required to construct the climbers, moor the counterweight, produce and deploy the cable, provide power, etc, doesn't exist
    • "space management" issues such as collisions with space junk, aircraft, etc, are going to be difficult at best to resolve
    • and because the above factors, financial backing for such an enterprise is all but non-existent

    ... let's just say I wouldn't be holding my breath waiting for the space elevator. Unless we can solve the problems involving manufacturing of carbon fibers with the appropriate properties (which is far from a sure thing), worrying about issues like Coriolis on the ascending climbers is like discussing how many angels can dance on the head of a pin.

  • The system will need to send electrons to the surface constantly, creating a massive current on a 32,000 mile line. Even if you J-Hook the thing over the point and bring it back into the atmo, it is going to make a mess.

    We are better off using this nano-reinforced material to either a) create a 1km wide column that is devoid of atmosphere (and hence no resistance) or b) create a 1km volume capable of containing vacuum, as per Diamond Age, creating the lightest possible lighter-than-air vehicles to SSTO.

  • by DynaSoar ( 714234 ) on Tuesday December 09, 2008 @10:15PM (#26054621) Journal

    Start with the space shuttle's tethered power generation experiments: []

    Multiply the power generated by the many orders of magnitude that the elevator is longer than the tether was.

    As the elevator swung through the magnetosphere on the aposol and perisol points of its rotation, it'd be generating billions of volts and conducting huge amounts of current down to the ground and out the top end of the elevator.

    The ground equipment and probably a portion of the bottom of the elevator would be turned to plasma. Same at the other end. The rest of the structure would orbit free and crash. Enough of it would not be burned away that the remainder would wrap around the Earth several times.

    Note that this scenario would require it be completely built before the effect started. This is, of course, impossible. It would be burning itself away as its length was increased. Note also that this is due to the structure only, not the dynamics of something going up and down it. Nothing would ever get the chance to make the trip.

    It is at first obvious that generating power in this fashion would power the elevator. Less obvious but more important, is what to do with the 99.999% of the generated power that's surplus. It's just too much surplus, and we have no technology to carry that much power safely on such a structure.

    Look at the details of the tether experiment. Less than 20 km of tether produced 3500 volts and burned the tether away from the shuttle. The elevator would be 4216 times longer. Also, the tether was not directly vertical, whereas the elevator would be. The amount of power generated would be more than the 4216 times the length.

    A primary choice for the elevator structure is carbon fiber. When that stuff burns it puts out a cloud of random buckytube-like particles which pose a health hazard much like a cloud of equivalent mass of asbestos. The best choice of material for the structure would be pretty near the worst choice when it came to its inevitable self-destruction.

    If the elevator burned away in the atmosphere, the carbon particulate would be a nasty pollutant. If the structure boiled itself away at higher altitude, outside the atmosphere, it would leave a trail of carbon particles that would become a hazard to spacecraft. Flying through that cloud would be like plowing into fine sand. A brief encounter would be very little trouble. But trying to fly at that same orbit for an extended time would erode away the spacecraft. If it were dense enough, it could also collect some charge in the manner of the tether, and discharge that into a spacecraft approaching it.

"The eleventh commandment was `Thou Shalt Compute' or `Thou Shalt Not Compute' -- I forget which." -- Epigrams in Programming, ACM SIGPLAN Sept. 1982