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Space Science

Calling the Space Elevator 72

Posted by michael from the keeps-hands-and-arms-inside-the-car dept.
CornfedPig writes "SPACE.com has an article that suggests building an elevator to a 100,000 km-high penthouse could be possible within the next few years at a cost of about $5B US. Widespread availability of low-cost carbon nanotubes appears to be the gating factor. Existence of such an elevator could drop the cost of lifting things (satellites, people, CowboyNeal) into orbit to a couple of hundred dollars a pound. Anyone remember Clarke's The Fountains of Paradise?" Space elevator stories come along every few months; we never seem to be getting any closer to actually doing it. I imagine it will happen at some point in my lifetime, but...
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Calling the Space Elevator More

Calling the Space Elevator

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  • Space elevators are a pie in the sky (or is that knife in the sky?) idea that won't work.

    Remember what is required, first. The thing has to come reasonably close to the ground in order to be useful. And the center of mass has to be at geosynchronous orbit height, 100 km up. That's a huge amount of mass spread over a very large area. This incurs several problems:

    • Tidal forces of the Earth on the structure call for superstrong material. Side tidal forces from the moon require it to be flexible as well.
    • How do you build it? Not in place...
    • Imagine that thing towering over your neighborhood. Pretty scary. Now realize that it is going to be visible from much of the Earth's surface and add NIMBY into the equation.
    • The voltage potential from top to bottom is going to make this thing deadly deadly deadly without ultra-secure precautions.
    • No, the theory is sound, the initial fiber would only weigh 20 tonnes, if you can achieve the necessary strength which right now we are a smidgen short of. The cable is very thin and flexes easily, so the lunar tidal forces are no problem. The paper says it would be built on an oil rig type structure on the equator, well away from dry land, so NIMBY is obviated.

      Voltages? I don't think anyone knows what would happen with that, as far as I know it wasn't mentioned in the original paper either. It might be soluble. Lightning strikes could spoil your whole day that's for sure.
      • I have read the same paper you talked about in your previous post. The writer does mention lightning strikes and discusses a few solutions.

        One solution is that the place where he proposes building it has on average 3-4 lighting strikes per year which is the lowest in the world. It also has the lowest number of storms in the world per year. Also, ocean currents make a sort of tidal pool area and hurricanes do not go into this section of the Pacific.

        Another nice thing about the design is that it will not be nearly as destructive as what everyone thinks of when they mention falling space elevators. One of the requirements for the glue for splicing the nanotubes is that it have a melting point that is below the heat experienced in re-entry. This means that all of the re-entering elevator except for the lower 60 to 100 miles of it will break up into little pieces each less than 10 cm in length and they will burn up on re-entry. The 60 to 100 miles that does not will fall into some of the emptiest ocean in the world.

        Also, to deal with winds, the shape of the cable is a cresent shape designed to face into the wind so that it does not flutter.

        As Mr. Clarke says "A space elevator will be built 20 years after everyone stops laughing."
        I'm not laughing, are you?
        • Another nice thing about the design is that it will not be nearly as destructive as what everyone thinks of when they mention falling space elevators. One of the requirements for the glue for splicing the nanotubes is that it have a melting point that is below the heat experienced in re-entry. This means that all of the re-entering elevator except for the lower 60 to 100 miles of it will break up into little pieces each less than 10 cm in length and they will burn up on re-entry. The 60 to 100 miles that does not will fall into some of the emptiest ocean in the world.

          But what about the cargo? I guess it's doable, to at least make sure that the cargo carriers break up on re-entry or have some sort of emergency survival option (especially if they are manned!) but that will be a lot more complex than the fibre itself simply breaking up.
          • In the design there is only 1 cargo pod on the elevator cable at any point in time. That is why they say that every 3 days something can be shipped up it. This is due to the fact that the propulsion system is a lazer that beams energy to the under side of the pod and the pod uses the energy to drive a motor with wheels that contact both sides of the cable. (And no, the lazer is not capable of cutting the cable)

            In a worse case scenario the cable would break before the pod reaches orbit (60 miles high if I remember correctly) and would become a falling projectile. However, in this case it would land in empty ocean. If it is above 60 miles then it would burn/break up and probably fall in the middle of the Pacific.

            Right now I can not remember the link to the pdf file the report was in but if you wish to read it, email me and I will send you the link.

        • One solution is that the place where he proposes building it has on average 3-4 lighting strikes per year which is the lowest in the world.

          The problem with using ONLY this solution is that, seeing as this is nothing but a giant grounding wire, every single of those 3-4 lighting strikes would hit the elevator.
          • Actually in the paper he has other solutions to deal with the lighting problem. Including the fact that since the cable is very flexable the base can be moved about in the ocean.

            In the report there is an analysis of all the different problems he and his team could come up with and multiple solutions for each of them.

            Right now I can not remember the link to the pdf file the report was in but if you wish to read it, email me and I will send you the link.

            Rich
        • 20 years might be plausible, but the actual quote is "50 years after everyone stops laughing."

          I've stopped laughing by the way. So clock is ticking. ;-)

    • Re:There's a reason we don't build them (Score:1, Insightful)

      by Anonymous Coward
      1. Geosynchronous orbit is much higher than 100 KM, try 35,786 KM (http://liftoff.msfc.nasa.gov/academy/rocket_sci/s atellites/geo-high.html)

      2. That makes a BIG navigation problem for all the satellites in low-earth orbit. Imagine a 36,000 KM cable going from the ground to Geosynchronous orbit, right through the path of thousands of assorted satellites, space junk, and the odd space station or two. All of the objects in low earth orbit will have a small, but ever present, chance of hitting our space elevator on each orbit.

      We'd have to make a tough elevator cable and actively defend it from such debris.

    • 'Buckytubes' (I hate that name) are within an order of magnitude of the strength required.

      The suggested building method is to put a bulky object (eg captured asteroid) in geosync orbit and lower the cable down, moving the 'roid back up slowly to ensure the centre of mass remains geosync.

      How thick do you think this thing'll be? I think that it *not* being visable is going to be a larger problem. ISTR that the core will only be of the order of a few centimetres diameter, you'd not see it at 100m, hardly a problem across "much of the Earth's surface"

      Voltage potential? You think the Earth circles the Sun because we're +ve and it's -ve? The only real issue would be a conductor moving through the Earth's magnetic field.

      You should call yourself PhysicsTroll, not PhysicsGenius...
    • You are talking about orbital towers. That is an outmoded idea.

      We will probably use a superstrong nanotube rope, instead. It would go out past GEO orbit. A weight, such as a smallish asteroid or something, would tethered past GEO. This would create tension on the rope, due to the counterweight wanting to fling off into space. This way, you would need no tower.

      Tidal forces of the Earth on the structure call for superstrong material. Side tidal forces from the moon require it to be flexible as well.
      Really? We would need a superstrong material to build 50,000 miles high? :-P We would use ultra-strong carbon nanotubes. About 60 times as strong as steel.

      How do you build it? Not in place...
      We pretty much know how to do it. We just have to improve our carbon nanotube manufacturing process.

      Imagine that thing towering over your neighborhood. Pretty scary. Now realize that it is going to be visible from much of the Earth's surface and add NIMBY into the equation.
      It would be extemely doubtful that it would crash. With the counterweight, should it become detached from the ground, it would fly off into space!!! Also, this thing is badass. IWLTH1IMBY(I would love to have one in my backyard)

      The voltage potential from top to bottom is going to make this thing deadly deadly deadly without ultra-secure precautions.
      You mean, kind of like a powerline??? If you touched a powerline you would be just as dead, if not moreso. Just put a fence around it.

      • Also, BTW, geo orbit is at 24,000 miles, I believe. The further you put the counterweight out, the smaller it needs to be. That is why 50,000 miles is a good length. As an added bonus, you can launch spacecraft off the end. A spacecraft launched from the end of the rope would fly off into space at an extremely high rate of speed. This concept is called tethers. It's just like if you swung a bola around your head and let it go, it would fly off and hit somebody in the head real fast.
    • And the center of mass has to be at geosynchronous orbit height, 100 km up.
      Your handle is "PhysicsGenius" and you think geosync is at 100 km? It's more like 35000 km.
    • Trees have been doing for a long time, just on a smaller scale. They may actually have to adopt a tiered design with multiple orbital nodes in geostat each connected at lower and higher points from the orbital node. This way the center of mass is always on-orbit, while lunar tidal forces (actually quite small even for an object this size), are laterally compensated for. The only serious problem I see is the longitudal drift caused by the moon.

      It can be built in place by adding from the orbital node up and down. Using small counterweights at each end, the ballance could be kept (though what keeps them from orbitting faster at the bottom and slower at the top escapes me...)

      High voltage problems? Use insulators every kilometer or so and use the differential to power the lift. I'm sure we have insulators with a much better dialectric than air.

      NIMBY is no problem at the equator if you build in at sea. (what's a kilometer of water after 100000 Km of vacuum and air?)
  • This is the type of thing that would have to be so heavily guarded that it would be a serious pain in the ass to use. There would most likely have to be some sort of wide radius no fly zone around it, as well as a very invasive search for anyone wanting to ride up. Very soon the reasons for not doing this will no longer be technical, but rather political and organizational.
    • I would like to go to space so much that I'd be willing to take the ride naked if I have to. This "serious pain in the ass to use" still seems like less of a pain than using a rocket.
      • I would agree. I'd be willing to take the ride naked while getting raped by a pack of wild gorilla's, but that still keep it from being a pain in the ass to secure an area that is in effect several hundred or thousand miles tall (How far is it too geostationary orbit?) and probably 100 miles in diameter.
        • but that still keep it from being a pain in the ass to secure an area that is in effect several hundred or thousand miles tall

          First off... their plans will only be a little over half of a hundred-thousand miles... ...second, the diameter will be very small at the ends of the elevator (less than a mile at the earth end... only 100mi at the center) third, Why would we need to defend all of those miles from terrorism?? ...do the terrorists have spaceships now??
          • No but if one or two or three manage to get a ride up there they might be able to do some damage.
            • Just because someone might catch a ride with a bomb on the elevator doesnt mean they need security posts along those thousands of miles... you stop the problem at it's source...

              I'm pretty sure that this space elevator won't available for normal civilians to take joyrides either (at least not for a very long time).... its not the airlines... All they would have to do is secure the ground section... and even more specifically the entrance to the elevator to make sure no unauthorized people get anywhere near it...

              ...they don't need to secure the whole thing...
    • You mean like the exclusion areas that (25 miles, IIRC) that are already established and working around launch areas? (And that were patrolled on launch days before 9/11).

      If you read the article, the current proposal is to put the earthside connection somewhere on a platform in the middle of the Pacific Ocean -- this should not be that difficult to handle.
    • This is the type of thing that would have to be so heavily guarded that it would be a serious pain in the ass to use.

      Yes, because if somebody snaps the line at the base, then we have the horrible result of...

      nothing at all happening. The line just hangs there, and it has to be reattached. Anybody heading up the line continues with no problem. No effect whatsoever.

      --
      Evan

      • Yes, because if somebody snaps the line at the base, then we have the horrible result of...

        nothing at all happening. The line just hangs there, and it has to be reattached. Anybody heading up the line continues with no problem. No effect whatsoever.

        Yeah if it leaves the structure in a stable state, but if you happend to break the structure in the middle, then it's not going to be stable. At that point you have a structure many miles high crashing into the ground.

    • There would most likely have to be some sort of wide radius no fly zone around it, as well as a very invasive search for anyone wanting to ride up.

      Whats wrong with a nofly zone?? They have tons of those all across our country over military bases...

      Invasive search? The only people going up on it would be trained astronouts, engineers, technicians.... all working for the government in some way or another, prescreened, and fully qualified to go up. It would be the same as shuttle launches... and does the average civilian go up there regularly???

      The general public won't have access to it for quite a while, if ever.

      The security will be fine for this... the only thing to worry about is someone breaching the nofly zone.

      If you're worried about other countries attacking it, forget it. This would more than likely be an international method of transportation, and shared with everybody like the international space station. The only people you have to worry about is terrorists... if they have a reason to attack it at all...

      • The general public won't have access to it for quite a while, if ever.

        I would beg to differ. There are only so many cheap satellites you can throw up there, and what not before that industry plateaus(sp?), i'd say maybe 10 years after the first one goes up. After that happens they will start looking at other uses for this. At that point it will most likely become a people mover.

  • Whenever I look at the Towers of light and the enourmous hight which it rises into the atmosphere.. I wonder if this is what a space elevator will look like. One of the striking things about it is how far the light penetrates into the upper atmosphere. From my rooof, 2.5 miles away, I was able to get a fix on the angle to the top and place the highest point I could see at about 15 miles up!

    For those of you who do not live out here, all I can say is that tv and photos simply do not do memorial any justice. It provides a humbling sense of scale when looking up into the infinity to which it rises.
    • You'd also have the weird effect that a hundred miles away or so on the ground, the top of the tower would be *clearer* than the base on the ground, as you are looking through a smaller wedge of atmosphere for higher elevation.

      Dr Fish
    • I'm looking out the window at the tower of light too (looks like 1 tower from NJ), and I'd I'd have to say no, a space elevator won't look anything like it. Imagine the towers of light, only 1/100 of the diamater and not lit up. It would be invisible at night and look like a line fading to nothing during the day (if you were close enough to see it, not more than a couple miles away).

  • The flesh is willing but the fiber weak (Score:3, Informative)

    by WolfWithoutAClause ( 162946 ) on Wednesday March 27, 2002 @04:13PM (#3236488) Homepage
    Ok, I admit it, I submitted the slashdot story before last on this topic, and I linked to the same paper that was mentioned in the next story, and this article is a piece on the same guy who wrote the same paper.

    Technically, the bottom line is:

    No we can't do this right now. The fibers aren't strong enough to do this without bankrupting the global economy. An exponentially tapering fiber can theoretically do this at any time, but it would be wayyyyyy too big and heavy to install. (e.g. a steel cable would be ~hundred meters wide at the thickest point, and >38000km long...)

    For the suggested construction technique, the carbon 'rope' needs to be able to give 72.5 Gpa strength, plus safety factor (typically 2). A single fiber gives about 73 Gpa right now. So we've no safety factor at all... but:

    Joining the individual fibers together- nobody has done this whilst maintaining enough of the strength. Splicing normally soaks up 15-30% of the strength, and so we're now 15-30% down on the required strength, and nobody has even managed to do splices this good with carbon fiber.

    Only a little percentage off then, but this pushes the mass up incredibly when you do the maths.

    Still, we're very close. 3 reasonably simple(?) breakthroughs (one to gain strength, one to splice the rope, one to actually scale up production from one 3cm fiber to trillions of 3cm fibers in a reasonable time) and we're saying 'Hi!' to the rest of the solar system.
  • Correct me if I'm wrong, but doens't using a space elavator to lift things steal from the angular momentum of the earth? I mean, you'd only lose a negligable amount from lifting satellites, and space stations, but CowboyNeal? I don't want to end up on the "permanant dark side of the earth".
    • Correct me if I am wrong (it's been a while since orbital physics) but since the payloads are being placed into Geosynchronous orbits, angular momentum is conserved. Since the two objects are still in the same system together, they keep the same relative energies (greater angular speed for the payload at a greater distance equals same energy). If they leave orbit, then I believe you may see a loss of momentum.
      • You still go around the earth once a day, but the distance you travel is much greater at geosynchronous orbit than at ground level; so you need to accelerate between the ground and GEO. i.e. Angular rotation rate is being conserved, not momentum.

        This means that as you climb the fiber, the fiber takes on a westward lean, as the earth tugs on you to help you speed up. So, the cowboyneal affect is real, although rather exagerated ;-)
  • from the article:
    "In 15 years we could have a dozen cables running full steam putting 50 tons in space every day for even less, including upper middle class individuals wanting a joyride into space. Now I just need the $5 billion," Edwards added.

  • WOW! (Score:2, Funny)

    by Anonymous Coward
    If we had a few hundred space elevators on the planet, how long would it take before we could move the entire mass of our planet into space?

    • Re:WOW! (Score:4, Funny)

      by WolfWithoutAClause ( 162946 ) on Wednesday March 27, 2002 @04:38PM (#3236656) Homepage
      > If we had a few hundred space elevators on the planet, how long would it take before we could move
      > the entire mass of our planet into space?

      The Earth is already in space. Amazing huh?
    • From the article we know we can move 50 tons per day. If the average person weighs 150 lbs. We can move 333 people per day per elevator. There are ~6.2 billion people on the earth and we are growing at 200,000 people per day. From this we can calculate that we would need ~600 elevators to maintain a constant population on the planet. (someone check my math)

      A few hundred more elevators and we could all leave I suppose, although it could take a while. I don't feel like doing the diffyq for this but it is rather striaght-forward to solve for the time to empty the planet.
      • thats way too expensive. Get a million people off the planet, maybe, after that just blow the rest up, its just not worth it.

  • For the consideration of others. (Score:3, Funny)

    by SuperguyA1 ( 90398 ) on Wednesday March 27, 2002 @04:41PM (#3236682) Homepage
    Given the length of time your ride on the space elevator and for the consideration of others. PLEASE do not ride the elevator after eating mexican food.

    Thanx,
    -The managment

  • Stabiliy ? (Score:3, Interesting)

    by 4of12 ( 97621 ) on Wednesday March 27, 2002 @05:14PM (#3236945) Homepage Journal

    Are there any astro uber geeks that can comment on the stability of this system from the standpoint of

    1. small changes of mass from the upper end of the elevator (like from space objects hitting and sticking, etc.)
    2. small oscillation modes (rubber band like) in the connecting fiber
    Otherwise, I'd be Real Nervous® about having the base station of the elevator anywhere near MyBackYard.
    • A factor in space launches IIRC is the wind velocity in the upper atmosphere, which at times can reach hundreds of knots [alaska.edu]. I also recall that the high wind velocity was a factor in the post-explosion breakup of the Challenger space shuttle.

      Although the atmospheric density and pressure is much lower at these altitudes (50-1000km+), the wind force is a factor, and it makes me wonder how a geo-stationary elevator shaft could be designed to withstand the energy of such wind forces.

      If it could work, it'd probably kick off a revolution in space industry.
      • There are extremely high winds at these altitudes. But the air is sooo thin it really isn't that bad. At 50 KM the air would be so thin that a 200 mph wind would be like a 20 MPH wind down here. Not so horrible.

        Really, wind force no matter at what altitude is usualy, but not always, the same as felt down here. Higher altitudes have higher winds but less force.
  • ....are The Fountains of Paradise [amazon.com] by Arthur C Clarke, and Feersum Endjin [amazon.com] by Iain M. Banks. Clarke came up with the ides of geosynchronous satellites, and Banks' book is an excellent hard-SF read.

    Dr Fish

  • Hypersonic Tethers will come first (Score:3, Informative)

    by Mad Bad Rabbit ( 539142 ) on Wednesday March 27, 2002 @08:19PM (#3237883)
    As other posters have noted, we don't have any
    materials strong enough for an elevator all the
    way to geosynchronous orbit, so it's a bit too
    soon for anyone to claim we could build one in
    the next 10 years.

    HOWEVER, we do have materials strong enough for
    a "hypersonic tether". This'd be a much shorter
    tether, only a few thousand km long, and moving
    at a good clip around the Earth, with the lower
    end just above the atmosphere.

    With this in place, you could use cheap sounding
    rockets, just barely capable of making it out of
    the atmosphere, to rendezvous with the tether as
    it swept past. The cargo would be grabbed by the
    tether and snatched up into low orbit, while the
    sounding rocket fell back to Earth.

    There aren't any good online references, but you
    can find USENET discussions of the technology on
    Google Groups, keywords "hypersonic tether".
    • Umm...right. Objects at high speed relative to each other meeting up in the air - see SDI for why that's tough (though, granted, in SDI one side is trying not to be hit). Even if they could dock perfectly, you've still got an instant high acceleration and mechanical vibrations that could easily damage the sounding rocket (to say nothing of anything inside the rocket). Oh, and once these tethers have given up some of their momentum to swing the rockets higher (you're not going to have a counterweight on each swing that you can detach, at least without a bunch of launches by other means and without a steady stream of travellers which doesn't exist beforehand), how do these tethers stay in the air?

      Tethers are slightly more real than the space elevator, granted. But there are far better ways to do SSTO that are even closer to reality...
  • ...now that's an oxymoron...
  • The BIG DIG [bigdig.com] i think is now over $12B although it was origainally estimated to cost $2.6B
  • The chief scientist at NASA Langley, Dennis M. Bushnell, gave a talk at my university a few weeks ago. He discussed several dozen *very* out-there ideas (personal auto-piloted helicopters for the masses within ten years, for example), but when asked about the viablility of the space elevator concept he dismissed it outright as a pipe dream.

  • Financial Aspects (Score:2, Interesting)

    by DiSKiLLeR ( 17651 )
    What i want to know is, would this be a good thing to invest it? They say it will cost $5bn, so they need money from SOMEWHERE, right?

    So say if i had a significant amount of money.. like $1million (hell, $500,000 or $100,000) and invested in the construction of this thing (or invested in a company that is constructing it by buying shares), would this be a wise investment, with good return?

    Would direct investment by supplying monies for construction and then demanding a % share of profits operating the elevator forever into the future be better then just buying shares in a company that is producing the elevator?

    Any thoughts?

    I'm always wondering what would be a very good sure bet for investment with VERY good returns, and something like these seems to be an ultimate one. The benefits of a space elevator are simply amazing, and the elevator will be in use for decades if not centuries, until replaced by something better, or a better elevator..

    Martin.

  • "Oh, hello Mr. Tyler. . . going down?"

  • could be possible within the next few years at a cost of about $5B US.

    Since development started in the early 1970s, the U.S. has spent over $180 billion on the space shuttle program. And what do we have to show for it? Certainly not reliable, low-cost access to space!

    $5 billion for a space elevator would be the bargain of the millenium.
  • For this idea to work its got to get past both the airline companies and their business partners that are setting up the old "Fly to outer space with 1,000,000 frequent flier miles (plus a hefty sum of money)". This assumes of course that there would be an option for tourism, but considering all the non-astronauts that are signed up for trips to the space station, I'm sure it would happen with this as well. I doubt those guys would appreciate losing business.
  • In his book 3001, the Earth's equator is studded with a series of tethered space platforms. Clarke's vision of these things includes a lot of interesting detail that I suspect is accurate.
  • [in abnegation of my nick...]

    Dr. Robert L. Forward in his 1995 book Indistinguishable from Magic, provides quite a treatise on the concept of Space Elevators or "Beanstalks" as the particular chapter is called.
    Forward has the scientific credentials to justify the idea with excerpts from existing studies to determine the physical and structural specifications of the tether.

    Forward also describes a variation on the tether idea that he calls a Rotavator- and that I've seen elsewhere called a skyhook; a rotating cable 8500 KM long in orbit at 4250 KM that dips down into the atmosphere moving at such a rate to allow it to pick up cargo/passenger modules from the earth's surface and swing them up into orbit for release at the apex of the swing either to go into orbit or meet up with an orbiting terminal.

    ...Probably the most lucid explanation of the physics and material requirements for space elevators that you'll find in print...

    [silent once more]

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