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Space Science

Space Elevator Could Cost Less Than You Thought 83

Posted by timothy from the pretty-soon-talking-real-money dept.
WolfWithoutAClause writes: "We've had Space Elevator stories before on Slashdot, mainly saying how impractical they are for the foreseeable future. Now however, there's an 8M pdf paper on NASA Institute of Advanced Concepts [NIAC] website that says it may now be possible with existing materials and can be done for about $40 billion. That's less than the entire launch market for a single year. If he's right, the first elevator may be complete in 10 years time, with the second and third following 2-3 years afterwards."
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Space Elevator Could Cost Less Than You Thought More

Space Elevator Could Cost Less Than You Thought

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  • 9/11 (Score:2, Insightful)

    by Anonymous Coward
    Not to bring up any bad memories, but if history has taught us anything - this will be a target. How could you keep something this long and lanky safe from planes?
    • Surface to air missiles and/or aircraft.

    • Re:9/11 (Score:2, Interesting)

      by xah ( 448501 )
      Who marked this post as flamebait? It makes a legitimate point.

      Among others, this "space tether" would be vulnerable to the following terrorist attacks: missle, bullet, bomb, acid, human piloted aircraft, remote controlled aircraft, ground vehicle, laser, and fire.

      These are just a few of the feasible methods to cut such a cable. If a terrorist wanted to place an infiltrator inside the space elevator, more attack options would be available to them.

      This space elevator idea doesn't sound feasible when the security problems it would engender are considered.

      • Don't forget one of the more obvious attacks, building a fuel-ladden craft that is to be raised on the elevator and which just happens to detonate while being raised. Depending on how tough the climbers are cable are, and how well protected the cable is from other attacks, it might be a practical attack channel.

    • It's a bit more robust than you think... (Score:2, Interesting)

      by Anonymous Coward
      First of all, if you break the cable down low, the bulk of it just "springs back" into an elliptical orbit with the same perigee.

      Secondly, a lot of plans call for the cable to join a 15 km high tower, since building up from the earth is feasible for that altitude, and chopping mass off the bottom end of the cable translates directly to increased cargo capacity. 50,000 ft is higher than most planes fly.

      The scary scenario is the cable breaking up high, e.g. the counterweight coming loose. The cable would fall to earth, wrapping around the equator multiple times as it does so, cracking like a whip. All of the energy spent launching it would come down in a long thin bang.
      • The risk of enormous destruction, I think, is a pretty good reason why sabotage is less likely to happen.

        Sure, I was surprised that the September terrorists were obsessed enough to kill thousands of people, some of who were their countrymen. But I think that the chances of any individual being prepared to do such a tremendous amount of damage to so many countries (Africa would be the worst hit) is slim.

        Maybe I'm optomistic. I know there are evil people around, but I can't imagine anyone wanting that much indiscriminate death.

        Anyway, I don't believe the risk is a show-stopper. Various possibilities, such as a self-disintegrating cable, quadrouple thickness, extraordinary security etc mean that this will one day be reality.
      • I got really, really suspicious when the article summary said we could have a space elevator for $40 billion. I said to myself, "Self, there's just no bloody way." And I was right.

        What the author of the study is proposing is a small elevator that takes things from the upper atmosphere to a point several hundred miles higher. This small scale is what makes it practical, and what makes it possible to propose such a thing without bringing up ugly images of an equator in flames.

        What would be really cool is a series of these small elevators, each pulling cargo up higher. It would be a great deal more fault tolerant and less risky than a single, monolithic elevator. It might also be a logistical nightmare. Further study would be required.
    • This would not be a target for terrorists because a space elevator would not be a symbol of US foreign policy.
      • You do make a good point that as long as it were not a symbol of policy or oppression then it would be safe. However, if such a structure were built and maintained by the US and somehow used to advance policy it could become a target in the future.
      • You make the dangerous assumption that all terrorists have the same agenda, or indeed, that the trrrorists responsible for the 9/11 incedent have only one beef.

        If you believe the US propaganda (which I neither deny nor condone), Al Qaeda is against all forms of personal freedom, and indeed against western culture and commerce (or even, simply, non-Muslims). If any of this were true, why not destroy such a pinnacle of Western technology? According to statements from various sources (Taliban and Al Qaeda sources as quoted by Afghani news sources), the triumph of the Sept 11 attacjs was that the world knows that America isn't invincible. The same point, in their mind, would need to be proven regularly, to set it in the mind of the citizens of the world that NO place was safe (and, by extension, that no act is unthinkable).

        And that's just Al Qaeda. What about some other religious whackos that decide that this structure is an affront to God (a Tower of Babel, if you will)? Indeed, no matter who builds it, it will be a target, just on account of its prominence.

        There are certainly ways to defend it, though they won't be foolproof. At least a one mile radius area around it will need to be a no fly zone, and fitted with sensors to deter unauthorized intrusion (since it will be in the middle of the ocean, this means sonar detectors able to detect people - indeed, probably some sort of underwater barrier around the whole mess). Costly, indeed. And yet, like most security in place currently, only as reliable as the people who operate it...
        • Good analysis. I'm sure that as soon as space becomes more accessible, some sort of "anti-Space" movement would erupt, whether for ecological, religious, or political reasons. Whatever the case, somebody's going to want to bring the thing down.

          What I think everyone has been missing so far is that we're not talking about a cable that stretches from sea level to geosynchronous orbit. The proposed project is an itty-bitty, free floating cable only a few hundred miles in length. The extensive security measures you describe would be absolutely necessary for a giant cable, but not for the elevator being proposed.
          • Okay, I'm an idiot, and should be moderated accordingly. While I was waiting for the PDF to drip in from my 28.8 modem, I was reading some of the links that the survey author had put up. Most of the reasonable sounding ones were describing relatively small projects a thousand miles in length or so. The PDF itself does indeed go all the way from ground level to geosynchronous orbit.

            Did I mention I'm an idiot? Okay, just checking.

  • It's a tether (Score:5, Informative)

    by Dr. Tom ( 23206 ) <tomh@nih.gov> on Wednesday December 19, 2001 @04:33AM (#2725093) Homepage
    This version of the Space Elevator doesn't go all the way to the ground. That's why it can be built with existing materials. You still need a (hydrogen fueled) rocket to get to the dock at the lower end of the tether, which is about 250 km up. However the dock is moving significantly slower than orbital velocity, which increases payload and allows cheaper (more reliable & maintainable) rockets.

    • Re:It's a tether (Score:4, Interesting)

      by bofh31337 ( 521771 ) <bofh31337@nosPAm.gmail.com> on Wednesday December 19, 2001 @07:32AM (#2725335) Journal
      A full 35,000km long space elevator would not be practical. Something of that great length would span many g-forces and you would need a large counter-weight above geo stationary to have zero velocity at ground level. Having that kind of taper from bottom to top would require a huge mass The big difference with a 250km tether is the center of attracting (and mass for that matter :)) can be in many more places. I'm thinking the best idea isn't so much a space elevator but a space slingshot using a pair or more of gravity stabilized fully rotating cables. It's an interesting idea that's been thrown around for many years.
      • > A full 35,000km long space elevator would not be practical.

        That's what I thought, but read the paper. He claims it's possible; and describes how, how much and how long. The carbon nanotubes are strong enough now; or atleast that's the claim.

    • Yes, it does go all the way to the ground (Score:4, Interesting)

      by iktos ( 166530 ) on Wednesday December 19, 2001 @08:11AM (#2725395)
      It's about a 96000 km, fixed at the bottom end, with a counterweight at the far end.

      It's 50 mm wide and with a cross section of 2 mm^2 (which makes it good for lifting 20 tons, payload 12, every 97 hours). But upgradeable, of course. Cable mass 572 tons, counterweight 621.

      Many parts of the building are pretty well thought out, like first sending down a thin cable and build the rest by having climbers adding more, and then using the used climbers as the counterweight. (Also, the climbers increase in mass as the cable grows stronger, from a total of 619 kg to 20 tons. Beam powered from the ground.)

      The initial cable would mass 19.8 tons, with fuel the deployer would mass 190 tons, but that's still a reasonable number of Shuttle missions.

      • Re:Yes, it does go all the way to the ground (Score:2, Interesting)

        by Anonymous Coward
        One of the interesting things about this design is that the counter weight must be in a strange state of having superorbital speed.

        Take the differential element of the wire that sits at the geostationary orbit. That element sits in geostationary orbit, and would be weightless.

        The thing is, all points on the wire would have to have exactly the same orbit time, if the wire is to stay straight.

        The counter-weight would ALSO have to have an orbit time of exactly one day. This means that it would be moving faster that objects would naturally at that orbital radius. How would that be done? By having the wire support tension, just like flinging the counterweight around on the end of a string under tension.

        The base of the wire would have to be attached to the earth in a very strong manner to support that tension.

        A nice pair of scissors would send the counter-weight into a very large orbit indeed. :-)
        • Not quite. If the counterweight is traveling faster than it should at that orbit, that doesn't mean that it would be launched away from the earth. Climbing the Earth's gravity well sucks away an object's kinetic energy. Unless the counterweight were traveling faster than escape velocity (for its current height above earth), it wouldn't go anywhere.

    • Re:It's a tether (Score:2, Insightful)

      by JohnPM ( 163131 )
      Not sure you were reading the same document as I was. The cable certainly does go all the way to the ground. Also, the cable described cannot really be built with existing materials because it relies on carbon nanotubes. While this material does exist, I don't believe it has ever been used as a construction material outside the laboratory.
      • While this material does exist, I don't believe it has ever been used as a construction material outside the laboratory.

        NASA may have its current problems, but it has a beautiful history of advancing materials science and using labratory materials in real world situations with incredible results. I do not doubt that if they set out to do this, and choose to use carbon nanotubes, that not only will it be built, and carbon nanotubes become a practical building material (in whatever level of expense they wind up settling at), but also that the public as a whole will forget that it was NASA that spearheaded the practical use of the material, and will continue to perpetuate the myth that NASA spent our tax dollar developing zero G pens while the Soviets used pencils.

        --
        Evan

  • What happens when this thing grounds the ionosphere? Prolly a stupid question, as I don't actually know if this is even possible, but I am curious to know if anyone else does.
    • David Gerrold (sp) just wrote a book a called jumping off the planet, basically set on a space elevator. One of the uses of the elevator is generating MASSIVE amounts of electricity from this sort of effect, which has to be managed by seling it, giving it away, or simply grounding it. Not a bad book set for the young to teenage coming of age story, but enjoyable by an adult.
    • That would probably be bad, although it might sort itself out, I don't know if anyone really knows what happens. I think that the tether would be designed to be an insulator.

  • the paper, not the slides (Score:3, Informative)

    by blamanj ( 253811 ) on Wednesday December 19, 2001 @02:14PM (#2727579)

    That 8M download only gives you the slides - pretty pictures but no text. The actual phase I paper is here [usra.edu]. It's a 15M download - and you can year the server creaking under the strain.

  • Angular momentum (Score:3, Insightful)

    by p3d0 ( 42270 ) on Wednesday December 19, 2001 @08:25PM (#2729788)
    When something's going up the elevator, where does it get all the angular momentum it needs to stay in orbit? Does the climber have rockets? I don't see them on the diagram.

    • Re:Angular momentum (Score:2, Informative)

      by CedgeS ( 159076 )
      You are probably not thinking about angular momentum, but energy in circular motion.

      Energy contained in circular motion is equal to:
      (This is the energy associatied with angular momentum)

      E = 1/2 I * (w^2)

      Where I is the moment of inertia and w is the angular frequency (in this case about 7.27 x 10^-5 1/s because the period of rotation will be 24 hours). The moment of inertia will increase as the load gets further away from the Earth.

      I = m * (r ^ 2)

      m is mass
      and r is radius from the center of the earth.

      So, the energy in circular motion at each height would be:

      E = 1/2 * m * (r^2) * (w^3)

      To get the formula for the total energy at each height, add the potential energy from Earth's gravitational pull.

      To answer your question, the increase in angular momentum of the payload is a result of the force exerted by the elevator doing work on the payload, resulting in a change in energy of circular motion.

      If you are worried about what is called conservation of angular momentum, the increase in angular momentum comes from a decrease in the angular momentum of the Earth. Conservation laws are usually written like so:

      initial = final

      So,
      L (angular momentum) initial = L final

      I forgot, angular momentum = I * w

      Where L is the sum of the angular momentums in the system.

      So,
      L(earth) + L(payload) + L(elevator) initial = L(earth) + L(payload) + L(elevator) final

      Because the radius from center of mass of the elevator and the Earth don't (negligibly) change during the lifting of the payload (this would affect I) and that for the payload does, the final angular frequency of something must be slower. Since they are all tethered together going at the same angular frequency, their angular frequencies must remain the same, and the anular frequency of the Earth will decreas very slightly (negligibly actually) and days will become slightly shorter while the payload is in space. You wouln't notice it though, because this happens every time any payload is sent into space -- every satellite space ship, etc.

      When you drink too much physics, alchohol just doesn't make any sense anymore.
      • You are probably not thinking about angular momentum, but energy in circular motion.
        Perhaps, but I really think I'm talking about angular momentum.
        To answer your question, the increase in angular momentum of the payload is a result of the force exerted by the elevator doing work on the payload, resulting in a change in energy of circular motion.
        How can you get angular momemtum arising from forces that act perpendicular to the direction of the desired orbit?
        If you are worried about what is called conservation of angular momentum, the increase in angular momentum comes from a decrease in the angular momentum of the Earth.
        The cable is not rigid, and unless I'm mistaken, it is perpendicular to the Earth's surface, so I don't see any way it can transmit a moment to the Earth.
        • > The cable is not rigid, and unless I'm mistaken, it is perpendicular to the Earth's surface, so I don't see any way it can transmit a moment to the Earth.

          You're exactly right. It can't be perpendicular to the earths surface and transmit moment to the Earth.

          In fact, as an object goes up the tether, it tends to drag the tether to the west, because the tether is accelerating the payload sideways as it goes up towards orbit at geosynchronous altitude- it needs a few klicks/sec up there relative to the ground, and its stationary at ground level, so it accelerates as it goes up the cable. The only way a cable can do that is to form a shallow v shape.

          This V shape means the tether is tilted to the ground. The tension on the tether at the ground will therefore pull on the earth and slow it down; but I wouldn't exactly lose sleep over that bit.

          In fact, the tether's position can be controlled by moving the payload up and down on the tether and careful timing.
    • Just guessing, but the angular momentum is presumably bled off the angular momentum of the elevator, in the same way that extending your legs whilst in a spinning office chair works.

      This is presumably a problem unless you then bring equal mass back down the elevator - why has nobody mentioned imports (people, rocks, deep frozen boze condensates, perfect diamonds and mass produced statues of aliens made out of 'genuine 100% space rock') here?
    • Looking at the slides, the climber appears to be powered from the ground by laser. Maybe they plan to power the elevator in the same manner. Hopefully it would not fry the contents or melt the cable.
  • At some point the cable would come loose from the counterweight. Maybe a meteorite would hit the counterweight, or a terrorist would cut the cable from that high location, or the fastener would simply give way. In any case, a worldwide disaster would result.

    The cable would fall to Earth. It would wrap around the Earth several times, as pointed out in another post below. The cable would stretch across continents, oceans, roads, railroad tracks, lakes, rivers, cities, residential areas, wildlife preserves, and many other areas. Thousands if not millinos of people would likely perish. It is conceivable that the entire Earth would shudder, literally.

    This is a project that should never be built.

  • Surely the demand to use this thing if it was ever built would be incredible. Everyone and his auntie would want an observatory up there, NASA would want to launch shuttle missions and whatnot from it, and many many multinationals would want to set up services to take people up on trips.

    Not only that, but how would waste (of all sorts) be disposed of? It seems an ENORMOUS pipe would be required to take everything down (although launching it into space would be simple, I suppose); and an even bigger pipe needed to pump up water and oxygen (with an equally huge compressor at the bottom to pump it up).

    I get the feeling that comments about it crashing into satellites and creating mountains of space junk are nonsense, but I also get the feeling that not many countries would be too pleased at America having a platform attached to land (or not; whatever) from which to spy on and potentially launch attacks from. It's sort of one step up from the spying capabilities of satellites, but I can't see all countries having space elevators very soon (though that would be cool).

    I' done with my ramble. Rip into my logic noww, please do. Destroy my sense of self-worth. ;)

    • The pipeline going down would invariably be smaller than the pipeline going up, and everything sent down the pipeline would end up saving energy, because it would balance a load coming up.

      America--and most other countries--will never have its own elevator attached to land, because a land-based one would have to be geosynchronous. Therefore, it'd have to be located on the equator. The one described in the paper is more free-floating, and would most likely either be located over the equator or spend time over most countries. In either case, the thing would be too easy to shoot down.
  • Firstly - they seem to have ignored the fact that a cable this long would snap under its own weight - even made of this carbon nanotube material. Ideally you want to maintain a constanst strain on the material throughout the tower so you need to start with very thick cable at the midpoint then taper it out towards the ends - the midsection would be maybe 10 times thicker.

    Now, even if they've accounted for this then the depolyment is in trouble, since they have to spool out the material from a drum, which means that you start spooling from one end or the other which means that you can't follow the ideal thickness profile without exceeding your structural limits during some point in the unroll procedure.

    The design for the deployment should instead extend the upper and lower half in both directions simultaneoulsy. The problem here is desiging a mechanism which can deploy this towards the end when the strain becomes highest.

    Another minor issue is how quickly you can deploy such a a large sturcture - the more patient the better, but you're dealing with 100,000km of cable - taking at at 10km/hr would take over a year to deploy, acceleration and deceleration of the deployment would induce oscialltions in the cable which would be difficult to damp...

    As for the danger of a break - not only would it fall down by wrapping itself around thew world a couple of times, but the tension on the structure would be like a strethed rubber band - the stored energy would be huge - think in terms of a nuclear powered rubber band.
    • Now, even if they've accounted for this ...

      Why don't you get a physics degree and submit your own paper.

      Or, here's a netball, left field idea - read this paper, see if you understand the math involved, and if not, drop back, read a bit more, figure out what we've learned about orbital mechanics, structural engineering and materials science over the past 8,000 years, and apply Clarke's second law.

      --
      Evan "Armchair physicist who knows where his knowledge ends and learning begins" E.

    • Man, do you even have the foggiest idea what you're talking about? You keep mentioning 100,000 km of cable. That's not what this guy is proposing. The "ideal cable" stretching all the way from ground zero to geosynchronous orbit is still a sci-fi dream, and you're insulting the guy by saying he's too stupid to realize that.

      The cable he's proposing is a much smaller one that would carry payloads from the upper atmosphere to a point a few hundred miles higher. There's no "wrapping itself around the world a couple of times." Just a nice, efficient little elevator for reducing the cost of moving materials into orbit.
      • Man, I don't have the foggiest idea what I'm talking about, and I certainly had no right to go blasting you like that. In fact, the proposed design does go all the way to the ground, and I was stupidly conflating this project with a less ambitious one I'd read about earlier.

        I still think that you're insulting Mr. Edwards by saying he wouldn't have taken into account the fact that the cable would have to support its own weight. However, after looking through the PDF, it's not beyond the realm of possibility that the guy is just a kooky graphic design major. He sure didn't provide a whole lot of detail.

  • Some great sci-fi reading, by Kim Stanley Robinson, has quite a bit about space elevators in it, and for all you who wish there were some type of utopian government... the problems that arise from building a society on mars. Excellent reading...
    • I agree, this is some of the best hard sci-fi ever written. On an aside do you know what happened to Fox's purchase of the film rights of the trilogy? I had heard it was being adapted as a miniseries for TV, and then the buzz died down and I haven't heard anything else about the project.
  • ... of current launch systems. Do we want and can we really afford to build redundant anchors, redundant cable spinners, etc.?

    We cannot even guarantee that a shuttle, or an Arianne, or an Energia will launch on a given date, or even that once it launches its payload will arrive at its intended destination. We have the technology to boost this kind of mass to orbit, but I suspect we do not have the reliability to construct this as inexpensively as the PDF's author supposes.

    With the risks entailed by a catastrophic failure of this cable I certainly want a spacecraft more reliable than anything we have sitting on launchpads today to maintain this beast. I want a better answer than "duck" if Dan Rather cuts into my evening TV to announce the cable has been cut by terrorists.

    I am afraid that if NASA were to bite on this idea (today) it would be one more megaproject fraught with massive cost overruns.

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