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Space Science

Space Elevator May Become Reality 465

Posted by michael from the skyhook dept.
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."
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Space Elevator May Become Reality More

Space Elevator May Become Reality

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  • vacuum gloves, radiation belts, high-velocity hardware...

  • Meet George Jetson! (Score:2, Insightful)

    by Anonymous Coward
    Not to dismiss the elevator out of hand, but wouldn't research into efficient space vehicle propulsion yield better long term results? While the engineering feat of building an elevator would certainly yield advances in science and technology, the elevator's limit would be its height. Non-tethered vehicles have no such limit.
    • Most of the effort of getting around, is getting UP. Once you get up its cheap to move around.

      Also, you can transfer fuel up by the tanker load.

    • Re:Meet George Jetson! (Score:5, Insightful)

      by mmontour ( 2208 ) <mail@mmontour.net> on Friday February 01, 2002 @08:23PM (#2940086)
      Not to dismiss the elevator out of hand, but wouldn't research into efficient space vehicle propulsion yield better long term results?

      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)

      by coyote-san ( 38515 ) on Friday February 01, 2002 @08:25PM (#2940096)
      Robert Heinlein (iirc) once commented that low earth orbit (LEO) is halfway to anywhere, and that's even more true of geosynchronous orbit (GEO). It takes a *lot* of fuel to get out of the earth's gravity well, and getting to GEO for the cost of electricity (provided by in-space solar cells!) would profoundly change everything.

      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.
      • Nasa already tried a long cable experiment. This one was probably made of metal though. They deployed a long cable from the space shuttle (i forget how long, but it was pretty darn long) and let it 'drag' behind. The idea was that as it dragged across the Earth's magnetic field, it would produce an electric current that the shuttle may be able to use.

        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)

        by matthewmichaelagee ( 555968 ) on Friday February 01, 2002 @11:00PM (#2940708) Homepage
        I studied this concept as part of a commercial space development group back when I was in college. It's quite compelling.

        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)

          by coyote-san ( 38515 ) on Saturday February 02, 2002 @01:21AM (#2940987)
          Another Robert Heinlein observation, this time from _Friday_. The issue is never energy, it's how the energy is stored.

          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)

          by Ungrounded Lightning ( 62228 ) on Saturday February 02, 2002 @01:47AM (#2941058) Journal
          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.

          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.

    • Spacehooks (elevators etc) are the most efficient way of getting into orbit by far and that's the trickiest part of space travel. Once you're in orbit it's fairly cheap to get elsewhere. The trouble with an elevator is not the efficiency it's the engineering requirements and disaster scenarios.

    • Re:Meet George Jetson! (Score:3, Interesting)

      by uchian ( 454825 )
      I can take a good reason to build an elevator straight out of a book called 'science of the Discworld'. Basically, the argument goes that if you have an elevator into space, then you can reuse energy, whilst if you have a propulsion system then you cannot.

      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)

    by saarbruck ( 314638 ) on Friday February 01, 2002 @08:05PM (#2940015) Homepage
    I didn't see anything in the .PDF about armoring the elevator against Vermicious Knids. It's just that sort of oversight that will be their undoing. Mark my words. Or Roald Dahl's. [amazon.com]

  • Last time this came up on /. (Score:5, Interesting)

    by Bill Currie ( 487 ) on Friday February 01, 2002 @08:06PM (#2940016) Homepage
    I did the math and worked out that if you gibbed the cable (say 1m chunks), you'ld wind up with something like 25-30 thousand km (I don't remember the exact figure) of the cable crashing down on earth and the rest flying off into space. However, I didn't figure out if the cable would fall east or west (west would be better, but I think it's less likely). Either way, that's a little over 1/2 way around the world and while the only land mass likely to be hit is Africa, I don't imagine the impact with the water would be particularly fun (possible tsunami).
    • actually it would wrap aroung the equator, fall west word, and wrap around the earth.
      The tram is "mega-tsuanmi". No I didn't make that up.

    • OT - Fiction for this scenario (Score:4, Informative)

      by Embedded Geek ( 532893 ) on Friday February 01, 2002 @08:29PM (#2940119) Homepage
      (Yes, it's off topic... Put away your flamers)

      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.

      • Mars is a much better place to experiment with spacehooks like this. It's easier to build them there, they don't need to be as big, and there wouldn't be the same disasterous consequences if and when something goes wrong. Larry Niven's written a fair amount about it, see for example The Barsoom Project.
    • You'd have to nail it high up for there to be any "damage". If you sever it at the bottom, you wind up with a free floating base that you can reattach. The point is that the entire elevator is in stable geosync orbit (actually, it's CM is in geosync), so that if the base is snapped, it doesn't fall.
    • Has anybody really sat down and worked out the physics of this thing if it were to collapse? How would the atmosphere effect it? How much of the structure would burn up? Most of the models for something colliding with the earth involve something that is one contained piece of mass. How does a big long rope like mass react during a similar collision?

      • Re:The physics of collapse (Score:4, Informative)

        by Bill Currie ( 487 ) on Friday February 01, 2002 @11:14PM (#2940739) Homepage
        Yes, I did, but simplifying things. I assumed the cable had somehow been shattered into small enough chunks that I could treat them as point masses, neglected the moon, sun and other bodies (mind you, for this they're negligable anyway), and worked out the near point (perigee? I never remember which is which between perigee and apogee) for the orbit of an object starting at the appropriate velocity for its height along the cable. I decided that any near point above the atmosphere would cause its orbit to be thrown out as `safe' and any below as potentially dangerous (due to burning up, it might still be safe). I chose somewhere between 90 and 100 (150?) km because I know that the space shuttle has stayed up at that altitude long enough that if it was a dangerous object, something could potentially be done about it. I assumed that anything that came below that mark would make a mess. My solution for the minum safe height was somewhere between 25-30 000 km.

        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 :)

    • Oh, please, go back to your caves and freeze to death why don't you!

      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...
    • How difficult would it be to cause such a failure? The article mentions the thing might be a terrorist target, and also mentions these carbon nanotubules are around 30 times as strong as kevlar. Bomb suits I've heard are around 10 layers of kevlar(I don't know the thinkness of those layers), so I'd think it'd take something on the order of an atomic bomb to cause a critical failure if you left reasonably excess strength in the cable.

    • 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)

      by WolfWithoutAClause ( 162946 ) on Friday February 01, 2002 @10:28PM (#2940594) Homepage
      No, this is covered in the paper. The tether would melt and reenter harmlessly above a 100km or so. Below that it would survive, but its a pretty predictable landing zone; and one of the cleverer ideas he had is building it in the sea where it won't hurt anyone.

  • SF Books (Score:2, Informative)

    by RetroGeek ( 206522 )
    Read Red Mars, Green Mars, Blue Mars (Kim Stanley Robinson)

    Read Fountains of Paradise (Arthur C Clarke)

    It's all explained in those books.
    • I believe Charles Sheffield had published a "science fact" article on beanstalks and a very thin short story involving one before either his novel or Arthur C. Clarke's contemporaneous novels came out.

      (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)

    by ScottMaxwell ( 108831 ) on Friday February 01, 2002 @08:08PM (#2940027) Homepage
    Of course, you won't be allowed to board the elevator if you're a drunkard, a liar or a cheater.
  • This [slashdot.org] space elevator thing [slashdot.org] sure is popular [slashdot.org] around here [slashdot.org].

  • see what happens when one of these break... (Score:4, Offtopic)

    by Zurk ( 37028 ) <zurktech AT gmail DOT com> on Friday February 01, 2002 @08:12PM (#2940041) Journal
    as shown in full gory detail here [schlockmercenary.com]. note the counterweight too.
    • I'm sure that it would do an incredible amount of damage (I haven't done any calculations to see how much) but the counterweight would fly out into space. To function as a counterweight it would have to have a net force (centripetal + gravity) outwards, away from the earth.
  • The line might generate a lot of electrical potential if it didn't remain stationary relative to the earth's magnetic field... Also, wouldn't things like wind, static electricity, lightning and auroras cause problems with a 22,000 mile long cable?

    • 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)

    by Guppy06 ( 410832 ) on Friday February 01, 2002 @08:16PM (#2940053)
    Because if it fell down, it'd be about as destructive as a thermonuclear bomb (kinetic energy's a bitch). And NOBODY would want this in their back yard after 9/11.

    On the moon, Mars, any other sparsely-populated/unpopulated body in the solar system? Sure. But not here.
    • Put in next to a large body of water and use the stablizers to crash it gracefully into the ocean.

      Now you just have to worry about Green Peace.
      • Put in next to a large body of water and use the stablizers to crash it gracefully into the ocean.

        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....
      • Now you just have to worry about Green Peace.


        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.

    • Rest asure, it's well be in the middle of the nowhere.

      It will have to be near the equator (geosync) for this thing to work.

      Sure sounds crazy, but this sounds awfully cool
    • This reminds me of a comment my parents made after taping Atomic Train (NBC) for me since NBC felt Coloradans were too feeble-minded to deal with the plot.

      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.
    • Not neccesarily. If you detach the cable from the base (Earth-Side) all that happens is you have to reattach it (Assuming the Space-Side can hold the cable in orbit.) Any prognosis of doom would have to come from detaching it from the space-side in which cause Earth's gravity would pull it down. Now, crashing an airplane into the WTC is one thing, taking down a orbiting space asteroid is quite another. (Of course in Kim Stanley Robinsons Mars series that is exactly what happened but..) 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.

      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!

      • 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)

        by Guppy06 ( 410832 ) on Saturday February 02, 2002 @02:21AM (#2941122)
        "If you detach the cable from the base (Earth-Side) all that happens is you have to reattach it (Assuming the Space-Side can hold the cable in orbit.)"

        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.
  • That's the book he wrote about this. Worth a read, it even describes some of the projects by the US and Russia concerning this decades ago, in the appendix.

  • Where's the info on the counterweight? (Score:3, Interesting)

    by pcx ( 72024 ) on Friday February 01, 2002 @08:18PM (#2940060)
    You can't have the orbital part without a counterweight otherwise you have gravity pulling down on the vast majority of the cable and the whole thing falls out of the sky. So you need a mass at the end of the cable so angular momentum holds everything up. Last I heard you needed a lot of mass to do that -- like a trapped asteroid or something -- far more mass than we havet he technology to put into orbit.
    • I think most serious plans suggest capturing an object already in space, not lifting it from the ground.

      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)

      by RedWizzard ( 192002 ) on Friday February 01, 2002 @08:45PM (#2940194)
      No, you don't need a counterweight. If the cable is long enough so that the center of mass is in geostationary orbit it will just hang there by itself.
      • No, you don't need a counterweight. If the cable is long enough so that the center of mass is in geostationary orbit it will just hang there by itself.
        And the tidal forces will keep it neatly stretched, too.
      • "No, you don't need a counterweight. If the cable is long enough so that the center of mass is in geostationary orbit it will just hang there by itself."

        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.
        • 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.

          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)

    by niekze ( 96793 ) on Friday February 01, 2002 @08:21PM (#2940076) Homepage
    they want to have a 22,000Km cable to space, but I can't get DSL because I'm 2.3 miles away...

    Grrrr

  • Okay,. who did that?! (Score:5, Funny)

    by Psiren ( 6145 ) on Friday February 01, 2002 @08:21PM (#2940078)
    Trouble is, if someone farts in the elevator, it's a damn long wait before you can open the door... ;)

  • here's a (slow) link in html format (Score:3, Informative)

    by headsling ( 310069 ) on Friday February 01, 2002 @08:25PM (#2940095)
    It's really slow, but it ain't pdf format http://www.niac.usra.edu/files/library/fellows_mtg /jun00_mtg/html/472Edwards/472Edwards.html

  • Damn! (Score:4, Funny)

    by Anonymous Coward on Friday February 01, 2002 @08:26PM (#2940107)
    I guess this obsoletes my "space escalator" idea then, eh?

  • Pie closer to hand (Score:5, Interesting)

    by Yurian ( 164643 ) on Friday February 01, 2002 @08:32PM (#2940133) Homepage
    Ok - The space elevator is a lovely concept, but it's only just possible with the theoretical limits of where we can go with materials technology - so its going to be pie in the sky (or lack there-of) for a long time yet.

    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)

      by coyote-san ( 38515 ) on Friday February 01, 2002 @09:29PM (#2940377)
      I was just out of college (iirc) when the first popular discussion of beanstalks came out (Charles Sheffield, in some long-dead Baen book-zine).

      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)

    by Junior J. Junior III ( 192702 ) on Friday February 01, 2002 @08:35PM (#2940141) Homepage
    But the weight to payload ratio sucks pretty hard. I imagine the up-front construction costs would be a lot higher than the cost of building rockets. So even if it's cheaper after, say, 10,000 uses, we might not see anyone wanting to build it.
    • Once it's up though, we could increase the amount of stuff we could put in orbit by orders of magnitude. As one poster pointed out, we could heft Nuclear Waste up this thing and chuck it towards the sun - not something we realy want to lift out of conventional orbit on a rocket. Dirt cheap sattellites. Family vacations to orbit. Assembling something like the one-shot Mars mission would suddenly become fairly easy and considerably cheaper. Ditto for space stations. The Benefits for humanity would be immense. It would really finally open space to us in a big way.
      • 20 tons is about the limit for conventional heavy lift to orbit right now, but if that's all that can be taken up at one time by what can only be described as a MASSIVE engineering project, it's going to create a pretty significant bottleneck in the long run, even if it is a considerable improvement over what we can do right now.
    • If you have a project with a more or less guaranteed return on investment, people will usually lend you the money. Besides, its easily in the range that the American government can afford- they spend 10x that per year outlay on space every year.

      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.
  • Ok, let's say that the destruction aspect of the tower isn't an issue, that the way this thing works means it could collapse in a (relatively) harmless way. I'm a little concerned with the whole idea of cheaply and easily getting things into orbit. Maybe I've read too much post-appocalypse Cyberpunk (spefically one of the stories in "mirrorshades") but it seems like there needs to be a *large* amount of regulation with what goes, because of what might be coming down... (like huge quantities of EMF blowing out pretty much everything electronic...)

  • Saving some cable... (Score:2, Interesting)

    by toby360 ( 524944 )
    I hope I don't get modded down for this idea like I always do but here it goes anyways..
    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.

    • 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.

    • One objection: Stability. The Earth is a basically immovable object as far as the cable is concerned, so tying it to the ground will ensure that it doesn't move. Putting it in the ocean is also pretty good. But air? There's little to push against. Also, there's the weight issue: I don't think even carbon nanotubes could support an entire airport, which would be a very difficult airport to design because of its single support point ("Would all passengers over 100 kg please move to the south side of the terminal?")

  • This Won't work - They forgot the taper factor (Score:5, Interesting)

    by szyzyg ( 7313 ) on Friday February 01, 2002 @08:45PM (#2940192)
    One big issue they missed is the fact that a carbon nanotube cable still isn't strong enough to support it's own weight without tapering the cable correctly, at the middle it has to be about 10 times thicker because the stresser are highest at geostationary orbit.

    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)

    by DarkZero ( 516460 ) on Friday February 01, 2002 @08:52PM (#2940225)
    If you'd like to see a surprisingly realistic sci-fi version of this, I suggest you take a look at Bubblegum Crisis 2040, an anime series that most geeks would really enjoy anyway, even if just for the interesting sci-fi ideas and the references to American sci-fi movies like Blade Runner and Alien.
  • The CBC Radio [radio.cbc.ca] science program, Quirks and Quarks [radio.cbc.ca] had an article about the space elevator on November 3rd, 2001 [radio.cbc.ca]. An MP3 of the article [radio.cbc.ca] is available. Check it out!

  • SciFi comes through again... (Score:4, Informative)

    by Utoxin ( 26011 ) <utoxin@gmail.com> on Friday February 01, 2002 @09:22PM (#2940351) Homepage Journal
    So many people read scifi and talk about how it's all just silly, and that it could never happen. Well, here's a list of things scifi has predicted that have come to pass:

    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)

    by WillSeattle ( 239206 ) on Friday February 01, 2002 @09:26PM (#2940366) Homepage
    Bungee jumping off the Space Elevator

    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 ... woah!

    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 ...

    -
  • Argh! Damn elevator! Here, let me pry open that door so we can climb---" (Big sucking noise)

  • Never happen (Score:2, Insightful)

    by John Jorsett ( 171560 )
    People go nuts when you suggest building a new nuclear reactor. What do you think would happen if you tell them you're going to multiply the potential destructive consequences of that by many fold, and suspend it over their heads? And the potential for an accident pales in insignificance if you consider how attractive a target it would make for someone to take down on purpose. I'm as big a techno-freak as anyone (hey, bring on those nukes, we need the power), but this would worry even me.

  • An article about this from August 1979 (Score:4, Interesting)

    by marko123 ( 131635 ) on Friday February 01, 2002 @09:53PM (#2940443) Homepage
    A sci-fi/sci-fact magazine in paperback form called Destinies had a story about this in their Aug-Sept 1979 edition. The story was called "How to Build a Beanstalk" by Charles Sheffield. He did some research into the material strength required, and to get the stalk to reach down to earth, or somewhere near it required a material with a tensile strength of 2 000 000 kg/cm^2, which was 10 times the current known tensile strength of known materials at the time.

    "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)

    by WolfWithoutAClause ( 162946 ) on Friday February 01, 2002 @09:54PM (#2940451) Homepage
    I've read this paper in full, a couple of months back. According to the paper the actual, demonstrated strength of the carbon tethers is only as strong as Kevlar- it's about 1/10 of the needed strength. The overall weight of the fiber is exponentially related to the strength, so the tether works out maybe 20,000 times heavier than his design- which makes it completely uneconomic.

    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)

      by Knobby ( 71829 ) on Friday February 01, 2002 @11:21PM (#2940752)

      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)

    by torklugnutz ( 212328 ) on Friday February 01, 2002 @11:24PM (#2940755) Homepage
    NASA is currently recruiting a team of flute-playing Snake Charmers to coax the cable into the air and keep it there. Send your demo tapes now!

  • Is this article a troll? (Score:3, Funny)

    by cicadia ( 231571 ) on Saturday February 02, 2002 @12:40AM (#2940897)

    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)

    by coyote-san ( 38515 ) on Saturday February 02, 2002 @02:09AM (#2941097)
    Something I haven't seen mentioned here (is the idea forgotten, or has it been proven to be flawed?) is the "construction ring" method.

    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!

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