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The Space Elevator 735

Posted by timothy
from the long-cable-long-review dept.
James Yonan writes "For years, the space elevator concept has been a staple of science fiction fare, popularized by Arthur C. Clark in The Fountains of Paradise, a convenient and plausibly feasible technology for building a vertical railroad of sorts, tens of thousands of kilometers tall, linking earth with geosynchronous orbit. Unsatisfied with the unquestioning consignment of the space elevator concept to science fiction status, authors Bradley C. Edwards and Eric A. Westling set out to understand why it could or couldn't be done. The result is a compelling new book, backed up by voluminous research, which concludes that space elevators are near-term-feasible. Edwards and Westling have not only convinced roomfuls of skeptics of the basic concept, but have also won serious funding from NASA for continuing their work. This book, The Space Elevator, is one of the fruits of their ongoing research." This is a long review (continued below), but the subject demands it.
The Space Elevator -- A revolutionary Earth-to-space transportation system.
author Bradley C. Edwards and Eric A. Westling
pages 280
publisher Spageo Inc.
rating 9 out of 10
reviewer James Yonan
ISBN 0972604502
summary A compelling argument, backed up with a great deal of quantitative analysis on both scientific and economic grounds, that a space elevator is near-term-feasible.

As a child in the late 60s and early 70s, some of my earliest memories are TV images of the moon shots, the sense of excitement and adventure, and confident assertions by adults that this was only the beginning, that progress was indeed unstoppable, and that it was a near certainty that by the time I was old enough to ask a girl out on a date, the question "would you like a ride in my spaceship" would be greeted not with derision, but with awe. Of course the sad reality is that none of this has come to pass. Space has remained dangerous, expensive, and inaccessible to all except the rare test pilot, scientist, or those for whom capitalism has been unusually kind. Luckily, there are some promising new ideas in space transportation that could represent the breakthrough we have been waiting for in the years since walking on the moon became passé.

In their new book The Space Elevator, Bradley C. Edwards and Eric A. Westling present a compelling argument, backed up with a great deal of quantitative analysis on both scientific and economic grounds, that a space elevator is near-term-feasible. The authors argue that carbon nanotube fibers are both strong and light enough that a 100,000 km elevator, constructed of a 2m wide carbon nanotube "ribbon," could be constructed in 10 years for a cost of US $6 billion, and be capable of lifting a 13-ton payload to geosynchronous orbit once every few days. If feasible, it would present a stunning breakthrough in space accessibility, and likely usher in a new age of space development and exploration.

Edwards writes in the forward:

One day, a few years ago, I read a statement that the space elevator couldn't be done, and I set out to find out why. From there, things got very interesting and resulted in a research proposal being submitted to NASA. The proposal was funded and resulted in, first a six-month study and then a two year study. The core of this manuscript started out as the technical report from the six month investigation I conducted for NASA under the NASA Institute for Advanced Concepts (NIAC) program.

Edwards and Westling begin the book with some history. Until recently, it was thought that alternatives to chemical rockets as a means to reaching LEO (low Earth orbit) were, at least for the foreseeable future, the stuff of science fiction. The idea of a space elevator, foreseen as early as 1903 by the brilliant Russian science speculator Konstantin Tsiolkovsky, foresaw a tower to geosynchronous orbit and beyond.

He was the first to identify the concept that the part of the tower beyond geosynchronous orbit would have an outward "force" due to Earth's rotation that would support the portion of the tower below geosynchronous altitude.

Essentially a space elevator is a geosynchronous satellite with an unusually high aspect ratio. So high, in fact, that even though the satellite is in orbit over a fixed point on the Earth's surface, the lower portion of the satellite actually touches the surface of the Earth. The key, of course, to making this concept workable is to find a material that has the tensile strength to withstand the extreme forces that such a tower or cable would be subjected to. Though a space elevator would need to reach 35,785 km to geosynchronous orbit, since gravity drops off as the square of our distance from Earth, we can collapse the 35,785 km down to its equivalent height as if it were all in 1g, giving 4940 km. This magic number represents the self-support height that a space elevator cable would need to exceed. The self-support height is the maximum length of material, formed into a cable, that can support its own weight in a 1g gravity field before breaking, and can be calculated by dividing tensile strength by density.

It turns out that a steel cable has a self-support length of 54 km, graphite whiskers (fibers) 1050 km, and carbon nanotubes 10,204 km. This last figure is an important result that shows that carbon nanotubes are significantly stronger than would be needed to build a space elevator. The difference between the 4940 km minimum self-support length and the carbon nanotube self-support length of 10,204 km all translates into significant payloads that could be lifted into space using this technology.

So if the space elevator is feasible right now for only US$6 billion (less than half of NASA's annual budget), why aren't we building one ASAP and preparing to retire the shuttles? The answer is that carbon nanotube technology is so new (invented in 1991) that we haven't yet created the infrastructure for mass production. In fact, the authors admit that we haven't even created a nanotube in the lab that demonstrates the requisite strength. While carbon nanotubes have a theoretical tensile strength of 300 GPa (billion newtons per square meter), strengths of only 11.2 to 64.3 GPa have been experimentally measured thus far. Edwards and Westling have heavily based their thesis on nanotubes reaching a tensile strength of 130 GPa in mass-produced volume, so they are to some extent reaching for the future here. Clearly they are counting on a kind of Moore's law to kick in, where the efficiency to cost curve of nanotube production improves exponentially as breakthroughs are made, then asymptotically slows as the theoretical upper bound is approached.

Now assuming that we can economically mass produce carbon nanotube ribbon at a strength of 130 GPa, what's next? Here Edwards and Westling present a well-researched plan for turning the raw material of the carbon nanotube into a functioning space elevator within 10 years. An initial kind of bootstrap cable would be lifted into LEO on board several trips of the space shuttle. This cable would be constructed of carbon nanotubes arranged in parallel with a reinforcing cross-connect adhesive, so that if a nanotube was severed, the remaining tubes would take up the load. The cross sectional dimensions of the cable would be highly asymmetrical, 1 micron in thickness, 13.5 to 35.5 centimeters in width, hence the cable is referred to as a "ribbon". After some assembly in LEO, the initial ribbon and deployment mechanism would be integrated into a spacecraft and sent to geosynchronous orbit, where it would deploy by basically unwinding the spool of ribbon towards Earth, while the spacecraft-spool assembly itself is boosted higher to maintain the total system in geosynchronous orbit. Once a few km of ribbon is unspooled, gravity gradient forces will kick in, ensuring a stable vertical orientation as deployment proceeds. Eventually the end of the ribbon would reach Earth where it would be anchored to a mobile sea-platform, located near the equator, which would have the capability to move the lower end of the cable to dodge known space-junk and electrical storms.

This prototype space elevator will be relatively weak and vulnerable to damage from meteoroids and uncharted space junk, so it will be essential to quickly strengthen the ribbon by widening it. Edwards and Westling's plan calls for "climbers" (electric-powered vehicles that climb the ribbon using a mechanical traction drive) to immediately ascend the ribbon, splicing additional carbon nanotube material onto the existing ribbon, then permanently parking at the far end of the ribbon to add to the elevator's counterweight mass. After 230 iterations of this process, the ribbon will be complete, 2m wide and capable of lifting 20 tons of climber + payload.

Getting a 100,000 km space elevator into position and insuring its survival is a daunting engineering challenge, and much of the book is dedicated to answering what-if scenarios and attempting to prove to the skeptical mind that such an ambitious undertaking is feasible. To this end, each space elevator subsystem is analyzed at length and competing solutions are evaluated for cost and efficiency.

For example three different methods for supplying electrical power to the climbers are evaluated:

  • run power up the cable,
  • beam power via microwave, and
  • beam power via laser.

Answer: use a laser.

An optimal shape (i.e. taper profile) for the ribbon is proposed, so that the part of the ribbon in the atmosphere is narrow to minimize wind-loading forces and the section between 500km and 1700km is widened and slightly curved to maximize survivability from meteoroid or space junk impacts. The destructive effects of wind, lightning, atomic oxygen, debris impacts, radiation damage, and ribbon oscillations are considered and solutions are presented. The conclusion: none of these adverse effects are show-stoppers.

Some basic FAQs are presented and answered, such as where does the energy come from to accelerate a climbing payload on the ribbon to orbital velocity. Answer: from the rotational inertia of the planet. If we shipped a whole continent into space, our days would get a bit longer.

After a comprehensive technical and engineering analysis of the space elevator concept, the authors move on to the economics of the concept and present a sort of skeletal business plan for "Space Elevator, Inc." They present many interesting uses for the space elevator including energy applications that could significantly improve the environment and reduce the combustion of fossil fuels. If the space elevator succeeded in reducing launch costs below $100/kg, large orbiting photovoltaic arrays might be built in space that would collect power and beam it to Earth via microwaves. These ideas are far from new (such an apparatus was patented in the early 1970s), but the reduced launch costs of the space elevator make them far more feasible.

The authors take a detour in explaining some promising results on the nuclear fusion front. Progress on the reduced-radiation IEF concept (Inertial Electrostatic Fusion) for fusion reactors would be accelerated by 3HE mining on the moon, which the space elevator would make feasible.

The rationale for building the ribbon up to 100,000 km is examined. The major advantage of such a tall ribbon is that the centripetal acceleration of the ribbon tip is substantial enough that payloads could be flung to Venus, Mars, or the asteroid belt with little additional energy expenditure. This, the authors argue, would bring down the cost of robotic planetary probes to the point where individual universities could afford their own space programs.

And finally, a working space elevator can be used to manufacture new space elevators at a much lower cost than the initial implementation. The authors suggest that the first significant commercial application of the space elevator might simply be in making additional space elevators and selling them to commercial clients. In this manner, elevators with payload capacities up to 200 tons could be deployed using wider ribbons, making possible a large-scale human presence at geosynchronous orbit and bringing the kind of commercial activities that would go along with that, such as tourism.

The book ends with a flight of fancy of sorts into a future where space elevators have become commonplace. Space elevators around Mars create an efficient Earth-Mars transportation network. Elevators on the moons of Jupiter throw spacecraft down into Jupiter's turbulent upper atmosphere to scoop up 3HE and ship it back to Earth in decade-long space convoys where it will power the latest and greatest IEF fusion power-plants.

While The Space Elevator goes a long way towards convincing skeptics of the feasibility of the general idea, the big question marks that remain in my mind are:

  • Will carbon nanotubes really reach the 130 GPa level in cost-effective mass production that will be required for elevator construction?
  • Much of the elevator deployment plans depend on the flawless execution of robotic mechanisms controlled remotely from Earth, including the trip from LEO to geostationary orbit, the deployment down to Earth, and the subsequent strengthening of the ribbon by robotic climbers that splice additional nanotube material onto the existing ribbon. As we learned with the Hubble Space Telescope, it is essential to have astronaut access for unexpected but critical repair missions. But much of the space elevator deployment will take place above LEO, out of access of human shuttle missions. What do we do if there is a glitch during deployment that requires an astronaut repair? We will need to seriously address such contingencies, lest we get saddled with a stuck elevator that could become the mother of all space junk.
  • Have there been any successful tether missions to date in space? While the answer appears to be yes, I would have liked to learn more about them.

Doubts aside, this is a compelling work that will likely become both a manifesto and bible for the space elevator movement, presenting a convincing argument that the space elevator is our best chance yet to bring Moore's law economies to space. It is an engaging read and I highly recommend it.


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The Space Elevator

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  • by boogy nightmare (207669) on Thursday March 06, 2003 @11:46AM (#5449056) Homepage
    Read Terry Pratchett's Science of Discworld books for more information on this......

  • Muzak (Score:5, Funny)

    by govtcheez (524087) <govtcheez03@hotmail.com> on Thursday March 06, 2003 @11:47AM (#5449060) Homepage
    Good Lord - the amount of Muzak one would have to listen to on the trip to the moon should be enough to stop a project like this in its tracks!
    • No, Space Muzak...

      heartsofspace dot com

  • by Ratface (21117) on Thursday March 06, 2003 @11:48AM (#5449064) Homepage Journal
    ... now I don't need to buy the book!

    Honestly, that was more of a synopsis than a review dont'cha think??

  • Plot. (Score:5, Funny)

    by grub (11606) <slashdot@grub.net> on Thursday March 06, 2003 @11:50AM (#5449073) Homepage Journal

    The whole space elevator thing is a conspiracy being run by The Illuminati. They plan to run wires up within the elevator shaft providing an unparalleled antenna for their mind control rays. At the top they are going to have a lounge and war room from which they can watch their world and plan our lives.

    Call me paranoid all you want, but it's about time the trut... oh just a sec, there's someone at my door...
    • Re:Plot. (Score:5, Funny)

      by sharkey (16670) on Thursday March 06, 2003 @12:47PM (#5449622)
      The whole space elevator thing is a conspiracy being run by The Illuminati.

      No, that's just a cover story for the true cover-up. What's really happening is that Travolta and Cruise are leading the Scientologists in a secret project to build an interstellar force-field Destruct-O-Ray to free Xenu. Since a 400 mile tall cannon would be rather conspicuous, they claim it is an "elevator to space".

  • by Anonymous Coward
    Now assuming that we can economically mass produce carbon nanotube ribbon at a strength of 130 GPa, what's next?
    Assuming that, it remains only to corral the unicorn, saddle up our flying pig and blast off! In-flight entertainment: Duke Nukem Forever.
  • dangerous?? (Score:3, Insightful)

    by in_ur_face (177250) on Thursday March 06, 2003 @11:50AM (#5449078)
    ok, so what if this damn thing falls??

    I dont know about you guys, but the whole concept seems flawed from the start. How about maintenance? What if the payload falls? I dont want to live anywhere near this thing....

    • by Anonymous Coward on Thursday March 06, 2003 @11:55AM (#5449106)
      If it falls, blame it on an oil-rich nation and invade. Duh.
    • Re:dangerous?? (Score:5, Insightful)

      by mrtroy (640746) on Thursday March 06, 2003 @11:56AM (#5449113)
      they plan on anchoring it off the coast of australia (or apparently thats a good spot for it) (i dont know why)

      and also apparently due to the forces acting on it if it did "fall" or break it would go flying off into space instead of collapsing on earth

      keep in mind how fast the earth is spinning! if you spin a basketball with a straw attached to it and the straw gets unstuck from the basketball...where will the straw go? It sure wont collapse onto the ball.
      • by spakka (606417) on Thursday March 06, 2003 @12:40PM (#5449533)

        apparently due to the forces acting on it if it did "fall" or break it would go flying off into space instead of collapsing on earth

        This would be worth it just for the look on the Al Queda pilots' faces.

    • If you don't want to live near it, either you better hope it never gets built or you'll have to find another planet to live on, because for something of that size, the whole friggen planet is "near" it.
    • Re:dangerous?? (Score:5, Informative)

      by krugdm (322700) <`slashdot' `at' `ikrug.com'> on Thursday March 06, 2003 @11:59AM (#5449133) Homepage Journal

      I seem to recall that the base of these things would be on large platforms anchored in the middle of the ocean, so if they did collapse, they would just fall harmlessly over water.

    • Re:dangerous?? (Score:4, Insightful)

      by RedCard (302122) on Thursday March 06, 2003 @12:01PM (#5449151)
      That's what they said about the eiffel tower, the CN tower, the first skyscrapers...
    • Re:dangerous?? (Score:5, Informative)

      by Anonymous Coward on Thursday March 06, 2003 @12:07PM (#5449202)
      read the initial feasability report. it (mostly) disintegrates as it falls to earth

      http://www.highliftsystems.com/convertedToHTML/n ia c_pdf/chapter10.html#impact
    • Re:dangerous?? (Score:3, Informative)

      by Vengeance (46019)
      Go check out the FAQ at High Lift Systems [highliftsystems.com] and see for yourself. It's not THAT much of a concern, because it's really a satellite, and wouldn't break orbit. The tricky bit is whatever is below the break, particularly payloads. The intended ribbon itself is incredibly light-weight, only 7.5 kg/km, and thus won't cause ridiculous amounts of damage.
    • by Inexile2002 (540368) on Thursday March 06, 2003 @12:17PM (#5449266) Homepage Journal
      Unless you're pretty much standing underneath it.

      This is one of those mass to surface area things. Although it would be freaking huge, if something happened which caused part of it to come down (which isn't what would happen, most would just sit there in space or drift away) it wouldn't be like a building collapse in one place.

      It would come down in pieces and most of the higher up junk would disintegrate. The stuff that was low enough not to disintegrate on re-entry would constitute a fraction of the mass and would come down in pieces scattered over a wide area of ocean. People at the base might have a really bad day but if you were not actually at the base facility you'd be in just as much danger as people were when Mir came down - ie not much.

      It's easy to get alarmed at the thought of the biggest structure of all time falling to the earth but in terms of actual danger to human beings the average sky scraper or speeding train presents a much bigger risk.

      As for falling payload, unless the payload was designed to survive re-entry and maybe fitted with a targetting system (which sadly is entirely possible) no one would be in any real danger. I mean, there is ALWAYS the possibility that something will fall from space and land on you, but if you're going to spend your time worrying about that you real problem is paranoia. You're hundreds of thousands of times more likely to die by slipping in the tub.
    • Take a look at This Study [usra.edu] That issue is covered.

      Take a look at section 10.9.1, page 64 of the PDF, which covers the "Severed Cable" issue in particular.

    • Re:dangerous?? (Score:3, Informative)

      by Jeremi (14640)
      ok, so what if this damn thing falls??


      If it falls, it breaks up and burns up in the atmosphere, or flies off into space. Wastes a lot of money, but causes no significant danger or environmental damage.


      I dont know about you guys, but the whole concept seems flawed from the start. How about maintenance? What if the payload falls? I dont want to live anywhere near this thing...


      It only seems flawed because you're not used to it. If you hadn't grown up watching rocket launches, you would think that throwing people into space via the force of huge chemical explosions was a flawed idea too. (it sounds like something Wily Coyote would try, doesn't it?)

  • by mrtroy (640746) on Thursday March 06, 2003 @11:52AM (#5449083)
    Why does Bush not say that his goal for America is to construct this during this decade? (similar to JFK, etc)
    This time in our history will be looked back at for terrorism, war, and world diplomatic struggles. Why not unite and construct something of this magnitude to unite us all? I am sure the terrorist strikes will stop themselves if the US gains a reputation for a R&D and science nation instead of a warring and military nation. If the U.S. put a 6 month hold on current military spending on new aircraft/ships/etc they could afford this construction 10 times over.
    • by Anonymous Coward
      Sounds like someone's already been takin' the space elevator...pretty early in the morning, no less!

      Anyway, everyone knows that the real reason that NASA got so much money was to beat the Commies. It WAS military spending.
    • "I am sure the terrorist strikes will stop themselves if the US gains a reputation for a R&D and science nation instead of a warring and military nation."

      i'd be worried of the terrorits flying planes into the space elevator :(

    • Why does Bush not say that his goal for America is to construct this during this decade?

      Well, to put it simply, he's not a complete and utter moron! Please, don't compare this space elevator lunacy with JFK. JFK proposed a difficult but doable task that was definitely within the nations technical capability. The space elevator is only feesible in the minds of those who have read TOO MUCH Heinlein.
      • Well, to put it simply, he's not a complete and utter moron!

        Um. Actually...

        ;-)

        The space elevator is only feesible in the minds of those who have read TOO MUCH Heinlein.

        Heinlein? Not as far as I know. Clarke, yes.

      • by pr0t0plasm (183810) <pr0t0plasm@lu c k y m u d .org> on Thursday March 06, 2003 @12:35PM (#5449446) Homepage
        Plus also he's got a missile shield to build, an occupation to run, a war to fight, another war to threaten to fight, a host of other countries to extend 'aid' to in exchange for complacency about those wars, multi-hundred-billion dollar 'tax breaks' (né 'kickbacks') to his campaign contributors... he's simply swamped!
      • by dasunt (249686)

        Heinlein had space elevators?

        **Thinks**

        Tunnel in the Sky : Transdimensional Gates
        Rocket Ship Galileo : Rockets
        Methuselah's Children : Rockets (I believe)
        Red Planet : Rockets
        Between Planets : Rockets
        Rolling Stones : Rockets
        Star Beast : Spaceships (I believe)
        Citizen of the Galaxy : Spaceships
        Moon is a Harsh Mistress : Magnetic Powered "Slings"
        Friday : Spaceships
        Orphans of the Sky : Spaceships
        Podkayne of Mars : Rockets
        Starman Jones : Spaceships and Rockets
        Starship Troopers : Rockets and Spaceships

        A note on the classification. I call anything that is propelled by throwing a mass backwards a "rocket", while any ship capable of intersteller transport that doesn't have its propulsion system explained is a "starship". And yes, this is all from memory (other then the book titles, which I googled for), so I have probably screwed up a few. Specifics that I remember include "the Rolling Stones", which was atomic rockets, "Friday" which was starships powered by a device developed by a lone inventor in his basement, and "Moon is a Harsh Mistress", which had magnetic "slings", to lift orbital material into space (it also probably had rockets, but I don't remember.) Some of Heinlein's later works *might* have had space elevators, but he seems to be a fan mostly of atomic rockets.

        Clarke used the space elevator in "The Fountains of Paradise", as well as "3001". I believe someone said that Ben Bova used space elevators in the "Mars" series. In the first Uplift Trilogy book, humans had created space elevators, which were made obsolete by the arrival of the Galactics - but still impressed them anyways (David Brin). A few other later authors had used the idea as well. IIRC, a Russian scientist proposed the idea first, under the name of "Sky Hook", Clarke picked up the idea for the Fountains of Paradise, which placed it on an island similiar to Sri Lanke, and other SF authors stole the idea from these two.

        Damn, just think about the social skills I would have had if I didn't spend my teens reading SF.

      • by JohnPM (163131) on Thursday March 06, 2003 @12:55PM (#5449722) Homepage
        Please, don't compare this space elevator lunacy with JFK.

        Um, I think you'll find it was JFK's Apollo program that was lunacy.

        Aaaahahaha.

        Moon. Luna. Lunacy.

        *tap*tap* Is this thing on?
    • by wind (94988) on Thursday March 06, 2003 @12:08PM (#5449208)
      I can't quite tell if you're serious with this comment... I don't think anger with the US will evaporate just because we stop trying to tell everyone what to do...

      But:

      Why does Bush not say that his goal for America is to construct this during this decade? (similar to JFK, etc)

      Because, despite his claims that he is a"unificator" and not a "divider-upper", Bush does not appear to have any real interest in "unificating" with other countries except to further US power. I know some (US) people will undoubtedly say that this is far better than working with other countries to weaken US power, but nonetheless, I can't imagine why someone who appears to have nearly no interest in domestic issues - let alone scientific research - would make this a funding priority.

      Unless someone could convince him that this could revive that whole SDI "Star Wars" thing...

    • by ArsonSmith (13997) on Thursday March 06, 2003 @02:29PM (#5450734) Journal
      You don't think that Christian terrorists wont try to attack this as being some sort of tower of babalon thing?

  • Wow... a Review! (Score:4, Insightful)

    by sielwolf (246764) on Thursday March 06, 2003 @11:52AM (#5449088) Homepage Journal
    This is probably more of a book review than what /. has been subjected to in a long time. It didn't feel like reading a 500 word essay that ended with "it was very very very very good."

    Of course there was less "review" and more "synopsis" than I would like. But then expecting the author to provide interesting critique might be a bit much. Overall much better than other reviews we've had.
    • by Jerf (17166) on Thursday March 06, 2003 @12:08PM (#5449210) Journal
      Of course there was less "review" and more "synopsis" than I would like.

      Different types of writing require different types of review. The type of "review" you seem to be asking for is really only appropriate for fiction. For a book of fact, the questions to answer are:

      1. What was the main point of the book? (Yes, that's a "synopsis". That's part of reviewing non-fiction.)

      2. How well did the authors justify that point?

      This review answers both those questions. Because the answer to number 2 is "quite well", that is relatively short, as it should be. It is much easier, and much more interesting, to list shortcomings then to list correct things. Are you really asking for them to write "All footnotes were written to modern standards. The title page was well-laid out and included correct Library of Congress information. Footnotes were correctly presented in 10pt font. The table of contents was complete and correct. The page numbers were correct."? These are things you assume until you have reason to believe otherwise.

      The answer to number 1 is importent in deciding whether you want to read the book or not, which is the final purpose of the review. In lieu of a lot of #2 to discuss, it should typically make up the bulk of the review for non-fiction.

      For a fiction review, it makes much more sense to talk about the intangibles, like style, characterization, and "relevance to the reader" or "the times". For a non-fiction book, it makes much less sense to spend much time on it unless it is either superb or atrocious.

      This review was fully appropriate to the book, and should be commended as such. Cynical observations that all reviews on Slashdot have looked like that, and this time it just happens to fit that subject matter, are left to the reader; I'll extend the author the benefit of the doubt. ;-)
  • by Kiwi (5214)
    The obvious question is this: How do we prevent a major diastar should the space elevator ever break? This is my one misgiving with a Space elevator: Should it ever break, you will have a ultra-strong cable thousands of kilometers long hitting the Earth. Think Deep Impact.

    - Sam

    • by CommieLib (468883) on Thursday March 06, 2003 @12:05PM (#5449177) Homepage
      Yeah, but what's the mass? Not giga-tons certainly, And as the Earth rotates, it seems to me that it will just kind of gently lay itself down. I suppose it depends on where the cable breaks...nothing like a Deep Impact

      Keep in mind that (it seems to me) the portion of the cable above the break will float up rather than falling down; the tether is as anchored to the Earth as it is suspended in space. Furthermore, it seems that this station will necessarily be situated in the middle of deep blue nowhere (because of air traffic control considerations), so whether we're talking about Ecuador or the Outback, the cable crashing slowly down is probably only a financial disaster.

      I think the main problem would be security. This cable would be a monument to humanity, and hence a prime target for terrorists.
    • by jms (11418) on Thursday March 06, 2003 @12:12PM (#5449236)
      Ok, I'll take a stab at it.

      If it were to break, it would split into two parts, each of which would either fall straight down or drift off into space. Remember, this thing is standing still relative to the earth's surface.

      If it were over the ocean as planned, the results would be a very unusual new reef.

      Depending on how long it took to descend, it would be dragged around by the weather, but it wouldn't go whipping around the earth at thousands of miles per hour, wrecking everything in its path.

    • The obvious solution would be to embed small explosives in the cable with devices to trigger them on any loss of tension. Then if the cable were cut at the top, *poof*, all you'd have to worry about is falling charcoal. The Red Mars space elevator cataclysm was a matter of poor planning, not an intrinsic flaw. (Of course, cutting the cable near the bottom isn't a threat to earth anyway, since the whole mess would just fly off into space)

      Moreover, after you've built the space elevator once, building a few dozen backups would be trivial and cheap, since you could run the new "starter" cables up the existing cable.

      A well-designed space elevator system could be entirely terrorism-proof.
      --G
    • Except that the cable isn't very heavy and is subject to terminal velocity like anything else.

      If the ribbon broke the top half would go off into space (presumably we'd have rockets to stablize the orbit of the elevator top). Why would it go into space? Because the top part is actually slightly past GEO sync orbit. Ribbon tension keeps it a constant distance from the earth.

      The bottom part would probably flap in the breeze... it wouldn't have much mass compared to its cross sectional area. The base is build on a platform at sea and we could probably reel in the tether faster than it drops.
  • by fobbman (131816) on Thursday March 06, 2003 @11:53AM (#5449094) Homepage
    Please, someone work on a good ventilation system for current elevators. Riding in an elevator with a woman with really strong perfume is bad, but when she gets off of the elevator and leaves you in there alone, and then two floors later someone else gets on and thinks that it is YOUR geeky butt smelling like that, it can be traumatic.

    Not this this has ever happened to be before...

  • Climbers - problem (Score:3, Interesting)

    by briancnorton (586947) on Thursday March 06, 2003 @11:54AM (#5449097) Homepage
    I have admittedly not read the book, but how exactly do the climbers get the material to splice onto the ribbon? Dragging up 100,000 km of CNT material seems really heavy, even if it is just a micron thick. Even if the ribbon can handle it, I have a hard time seeing a crawler that could carry that much.
    • Take a look at This Study [usra.edu]. Each of the climbers takes as much as the current cable can bear.

      So the first climber will take up a single strand to the top(or some such), doubling the capability of the cable. The next climber will take two strands up - doubling it again. And so on.

      The study also has "sample" designs of a climber in it.

  • by Niles_Stonne (105949) on Thursday March 06, 2003 @11:55AM (#5449099) Homepage
    I think that the Space Elevator is a really good idea, and there have been some very interesting(and detailed) studies of the feasibility.

    Previous Articles:
    Space Elevators: Low Cost Ticket to GEO? [slashdot.org]

    More on Space Elevators [slashdot.org]

    Going Up? [slashdot.org]

    Calling the Space Elevator [slashdot.org]

    Space Elevator May Become Reality [slashdot.org] - The Linked Study(PDF) [usra.edu] Was fascinating.

    Space Elevator Could Cost Less Than You Thought [slashdot.org]

    Stepping Closer To The Space Elevator [slashdot.org]

    I want to walk into an elevator some day and see two buttons - "G" and "O". (Ground and Orbit)
  • by Matey-O (518004) <michaeljohnmiller@mSPAMsSPAMnSPAM.com> on Thursday March 06, 2003 @11:55AM (#5449104) Homepage Journal
    When a suicide bomber sets himself* off at 45,000 feet?

    * = and it invairably seems to be a 'him', I think women are just genetically smarter that way.
  • by DavidpFitz (136265) on Thursday March 06, 2003 @11:55AM (#5449109) Homepage Journal
    If the space elevator is feasible right now for only US$6 billion (less than half of NASA's annual budget), why aren't we building one ASAP and preparing to retire the shuttles?


    NASA already is funding this kind of research. They have already invested $600,000 into Seattle-based company High Lift Systems [highliftsystems.com], according to a BBC article. [bbc.co.uk]


    Sounds to me the right thing to do -- invest in other companies to do the ground work, and see if it really is viable. If not they go bust -- Oh well. If it goes well, then great!

    • "If the space elevator is feasible right now for only US$6 billion (less than half of NASA's annual budget), why aren't we building one ASAP and preparing to retire the shuttles?"

      Because it's NOT feasible right now, for only $6 billion or any amount.

      And yeah, and the space shuttle was gonna put stuff into orbit for $10/lb. and launch every week. What a crock.

      I must confess that intuitively, it sounds impossible to me. A 40,000 km string! Can you just imagine the harmonics on this thing when the jetstream plucks it (or whatever). Hello! Atmosphere! Weather! Not the beautiful calm vacuum of space.

      And the geosynchronous terminus at the other end... a geosynchronous orbit doesn't maintain a precise spot over the earth. It wanders here and there in response to a number of influences. Not much, but if one end is supposed to be tied to the ground... The whole concept just seems off the wall to me. Fun! A cool idea! But off the wall.

      It sure is tough to get off this damn planet, ain't it?

      • by Jerf (17166) on Thursday March 06, 2003 @12:35PM (#5449443) Journal
        Because it's NOT feasible right now, for only $6 billion or any amount.

        Because . . . ?

        I must confess that intuitively,

        Oh. Your intuition. I guess we should give up on this right now.

        Can you just imagine the harmonics on this thing when the jetstream plucks it (or whatever).

        I don't have to imagine. I have computers. I can model the questions. Obviously, I personally haven't, but the people writing this book have. While I have not read this exact book, the atmospheric effects have not been neglected in the other treatments I have read have not, and they aren't much of a problem.

        They are certainly more intelligent then your analysis. Talking about harmonics in this situation is a crock of shit. The exact "resonance frequency" depends on the tension, but over tens of thousands of kilometers you're talking something that is a vanishing fraction of a Hz! At that point "resonant frequency" is meaningless, you're just talking about tension propogating.

        Given the failure of human intuition to handle large numbers, which you see routinely on Slashdot, I gotta say I'm much more inclined to believe a well-researched book then your intuition, or mine either for that matter.
  • than the World Trade Center. Imagine planeloads of terrorists and religious extremists trying to make their point by colliding with the "elevator". Heck, for that matter imagine some unwitting student pilot in a Cessna.
  • I know this subject has been cover before on slashdot. I think the idea is awesome. Of course I can't figure out how this all works I assume that the tip of the elevator would have to be massive and be travelling pretty fast. It would eventually sink back down to Earth just like the ISS does (it needs a boost back up every now and then).

    Maybe this sounds like a great book to understand all that. I might just go pick one up here [mediagab.com].
  • by Jerf (17166) on Thursday March 06, 2003 @11:57AM (#5449123) Journal
    The good reason to reach for this which can't be emphasized enough in the current environment is that for a relatively modest investment, the impact on the economy would be enormous (and good). Compared to other proposals to jumpstart the economy, this one has incredible bang for the buck.

    Obviously this isn't a short-term, instantaneous fix, but this is exactly the sort of project that something like the United States should undertake to help maintain its lead in the economy, if it is interested in maintaining it. The economic advantage of having the only working space elevator (even if it was only until we could build another for someone else, assuming optimistically we wouldn't build ourselves a few backups first) in the world would be absolutely incredible.

    Considering the price, it's complete foolishness not to pursue this, even if common sense says the opposite. And the best news of all is that carbon nanotube research is interesting enough on other, more commonly-sensible grounds, that it's going to continue anyhow.

    Another thing that should be emphasized is "Suppose China gets there first." Personally, I'd love to see a space race over this issue. It would be one hell of a lot more productive over the long term then the moon race was!
  • Even if the space elevator could be built, how would one defend it against terrorism. It would be kind of a big target at 22,241 miles high.
  • by mark-t (151149) <markt@@@lynx...bc...ca> on Thursday March 06, 2003 @12:00PM (#5449147) Journal
    Although it would require many, many tons of payload delivered into space each day...

    Getting rid of our garbage -- do you know how much cleaner cities could be if we could just send garbage to the sun???

    • The earth is a closed system. Our garbage, though it may be destroying the *present* environment, is an important part of that closed system. Removing significant amounts of almost anything, even garbage, from the earth will have a far greater and worse effect on mother nature than anything else we have done so far.

      Right now, we may be killing our environment with our garbage. But, after we are gone the earth will continue. If we remove significant amounts of anything from the earth, it will likely die and be like the moon.
  • So good, in fact, that I don't need to read the book. Thanks James! :)
  • Newby question here (IANAPhysicist), but wouldn't the elevator be a heavy load on the satellite supporting it? Wouldn't it exert a force downward towards the earth, thereby forcing it to continuously pull up to counter that force?
    • I think you have to place a counterweight past (at? IANAPhysicist either) the geosynchronous point.
    • by Jerf (17166)
      The space elevator satellite also extends a cable outwards, which balances the gravity experienced by the bottom part with the centrifugal psuedo-force on the top part.

      This is also why a break on the planetside isn't the disaster most people think it would be; the part below the break falls to the earth, probably at not too great a speed, and the part above the break floats out into space.

      A break above the satellite is worse, but there are ways of helping that too. One interesting, albiet possibly controversial idea, and bear in mind I'm just thinking of this right now, is to deliberately set up explosives/chemicals to cut the elevator at certain intervals, so if a break does occur, you cut an equivalent amount of the cable off the other end so the body of the cable and the satellite are still salvagable.

      Also, since you can lift so much, any manned vehicle can be made safe as long as the explosion doesn't occur onboard (obviously); there's enough weight available to make a vehicle that can land safely on the Earth. (Look at the pods for the Apollo missions; it doesn't take too much to splash-down safely, compared to what it takes to get that high in the first place.)
  • by jonbrewer (11894) on Thursday March 06, 2003 @12:02PM (#5449159) Homepage
    Let's hope this space elevator's fibers are a little more sturdy than the mast of Team NZ's yacht.

    "AUCKLAND, New Zealand The meltdown of Team New Zealand, the America's Cup defender, continued on Friday when, on the third leg of Race 4 against the Swiss boat Alinghi, the Kiwis' mast exploded into a heap of carbon fiber shards."
    (NYTimes)
  • by GeckoX (259575) on Thursday March 06, 2003 @12:02PM (#5449160)
    I totally believe that Space Elevators are feasible in the near term. However, my concern is with whether we should. Is there a compelling enough reason that outweighs the risks involved to actually go and build one of these?

    What risks you may ask?
    Well, sure, shuttles are quite expensive to launch and are not flawless by any means. But what was lost recently? 7 lives, a bit of research and a relatively moderate chunk of change.

    Ever thought about the effect of a disaster with one of these elevators? Use your imagination. Now remember that you have to use your imagination to even allow the concept of these being built so you can't just write off the possible effects of a catastrophe just because it's unlikely or far fetched...the whole idea is so if the idea becomes reality, well, likely so do many of the possible disasters that could come along with it.

    Ever heard of the plan to build a dam across the mouth of James Bay, separating it from Hudson's bay? It was fully engineered and can be done...thank GOD nobody with more cash than sense has decided to back this idea.
    Neato factor just doesn't cut it for me, I need real reasons that outweight the risks.
  • The Space Elevator

    * Cost: 500
    * Prerequisite: Super tensile solids
    * Benefits: Doubles energy reserves production at this base and doubles mineral production rate at all your bases when producing orbital improvements; your units equipped with drop pods may now make orbital insertions anywhere on Planet; this project also waives any aerospace complex restrictions on orbital improvements.


    We estimate that during the next mission century most of Planet's industries will be moved off-planet to Nessus Prime and other orbital facilities. Many of our industries will benefit greatly from the low gravity environments available in space, particularly those involving genetically engineered microbes.

    CEO Nwabudike Morgan
    "The Centauri Monopoly"
  • Considering that a small paint fleck travelling at 20,000 kph can imbed itself [shu.ac.uk] through several layers of lexan, what's to to stop stray bolts from constantly clipping this thing in two?

  • If the real and only cost barrier is carbon nanotubes, it seems like the best way to get this all to happen is to reduce the cost.

    Okay, okay, you're saying, that's obvious. However we could look at another scenario to see how such things are possible:

    Say we're sitting in 1983 or so, and we're saying, boy, it would be nice if all universities could have supercomputers and massive 10GB storage arrays to do computational exercises. Looking back 20 years, we know that's basically possible. The desktops of today were the supercomputers of yesterday.

    So, let's figure out how to spread the cost. How can we incorporate carbon nanotubes into equipment that everyone needs/wants to use? Does it mean integrating it into automotive equipment? Consumer electronics? Clothing? What?

    What would be the killer business/consumer application for carbon nanotubes?

    If we assume that cost is a function of production size and research money, the best way to up both is to provide a market that's not pie-in-the-sky (forgive the pun). We can have cheap nanotubes in 10 years, but it seems that the best way to do that is to make nanotubes common everywhere, not by utilitizing the NASA budget (which is going to be under heavy scrutiny after the latest disaster).

  • Even if something like this can be built and erected, how long would it last before it needed overhaul or replacement? Parts wear out, even carbon nanotubes.

    Maybe there's a nanotech solution so that tiny repair robots can constantly be working on maintenance. How close are we to nanobots that can handle such a task?
  • by TomatoMan (93630) on Thursday March 06, 2003 @12:06PM (#5449192) Homepage Journal
    How can I be a part of this? How can I be involved in making it happen? I probably have no skills that would be relevant (unless they need a database backend designed and some Perl kung-fu for some reason), but I'll do anything. I'll sweep up at night. I'll make coffee and donut runs for the engineers. Anything. Just let me be involved somehow. I'll quit my job right now and move to Australia or wherever and live on bread and water and raw dreams.
  • Why (Score:4, Interesting)

    by Hellraisr (305322) on Thursday March 06, 2003 @12:07PM (#5449198)
    Why does this remind me of Fred Flintstone using his feet to propel his car forward?

    I guess any space technology improvement is a good one, but does it really need to be so brute-force-ish? Whatever happened to the NASA of old that created the shuttle?

    They say that the next generation of space craft is still many years off, but I bet money could dramatically reduce the time frame (money always fixes problems like this - yay capitalism!)

    I think it is good to at least gaze into the future of possibilities and while this certainly would make for cheap satellite launches, etc.. I am skeptical at how safe it would be to send humans up or back on it..

    Say it comes to a grinding halt 1/2 way up. What on earth do you send to rescue the people off it this time?
    • Re:Why (Score:5, Insightful)

      by Jeremi (14640) on Thursday March 06, 2003 @01:30PM (#5450103) Homepage
      I guess any space technology improvement is a good one, but does it really need to be so brute-force-ish?
      Whatever happened to the NASA of old that created the shuttle?


      You consider blasting yourself into space on top of a giant, fuel-guzzling, uber-polluting tower of burning noxious chemicals more graceful than simply climbing up at a leisurely pace? I think you've got it backwards.


      I think it is good to at least gaze into the future of possibilities and while this certainly would make for
      cheap satellite launches, etc.. I am skeptical at how safe it would be to send humans up or back on it.


      I think you are suffering from a blind spot -- just because rocket launches are what you're used to doesn't mean they are "safe" by any stretch of the imagination. Getting into space by means of a space elevator (where a malfunction means you can simply abort and safely descend again) is much safer than by rocket launch (where a malfunction means you will be either blown into a million pieces or fall to the ocean to be smashed flat)


      Say it comes to a grinding halt 1/2 way up. What on earth do you send to rescue the people off it this
      time?


      Most likely, people in the elevator would just evacuate to the escape pod, which would then use friction braking and gravity to deliver them safely back to Earth. Afterwards, a climber vehicle could be sent up to fix or remove the broken elevator.

  • Otis

    A wholly owned subsidiary of United Technologies Corp (UTX).

  • Interesting analysis of the materials. I wonder what the self support length of other materials might be. Like spider's silk, which is claimed to have tensile strength far greater than that of steel.
  • I always wondered what the "climbers" would hold on to. Carbon nanotubes are probably a bit slippery, like graphite. Are they going to punch chain holes in it? Also, how do the climbers adjust for the changing width and thickness along the ribbon?

    Obviously the answer is not a space elevator, but a space escalator. Make it an endless belt that can be rotated. Provides a two-way transportation path, as well. The mass would have to be much larger though (continous profile along the entire length).
  • by pcraven (191172) <paul@@@cravenfamily...com> on Thursday March 06, 2003 @12:15PM (#5449246) Homepage
    I worry if we make the cost so small, we'll have an artificial ring of space debris around our planet and we'll never be able to get out of here.
    • My vision is of "Earth as a porcupine."

      Once the first is complete, second and third and more will be much cheaper to produce. We could have a Space Elevator in every city.

      As for debris, once we have nanotechnology we'll easily be able to both identify (and collect) particles of the smallest size that could damage ships; and also we'd be able to harden the ships to withstand greater damage (they would even be self-healing, so if a rock would punch a hole through it, the ship would just create a temporary "tunnel" through itself for the rock and avoid a collision completely).

  • by rpiquepa (644694) on Thursday March 06, 2003 @12:15PM (#5449251) Homepage
    Besides previous Slashdot stories about NASA's space elevator project, I also wrote several columns about this concept in the last months. If you're interested, take a look at "NASA Plans Elevators to Space [weblogs.com]," "Pushing the space elevator closer to reality [weblogs.com]" or "Space tourism 'viable at $15,000 a seat'? [weblogs.com]."
  • Going up?
  • This has far too many practical applications.

    If you want to build a monument to humanity, I suggest we carve a peace symbol on the moon.... using nuclear weapons.
  • by chiph (523845)
    The book/article mentions that the ribbon will initially wound on a mechanism in LEO, and then unwound during deployment to a floating platform on the equator. Just wondering what the minimum bend radius is for nanotubes. If you wind it too tightly, you'd fracture a lot of the tubes, significantly reducing the ribbon's strength (you'd be relying on the cross-tube adhesive more than before).

    Chip H.
  • by handy_vandal (606174) on Thursday March 06, 2003 @12:38PM (#5449491) Homepage Journal
    <Obligatory Simpsons Reference>

    A news report on the Space Elevator comes on the TV.

    Kent: But there's already one big winner: Our state school system, which gets fully half the profits from the Space Elevator.

    Skinner: [talking with his teachers] Just think what we can buy with that money... History books that know how the Korean War came out. Math books that don't have that base six crap in them! And a state-of-the-art detention hall [holds up a scale model] where unruly children are sent to Space Elevator detention.

    Teacher: [to no one in particular] Space Elevators. Always with the Space Elevators ...

    </Obligatory Simpsons Reference>

    [With apologies to Dog of Death [snpp.com] episode.]
  • by thasmudyan (460603) <udo.schroeterNO@SPAMgmail.com> on Thursday March 06, 2003 @12:42PM (#5449554) Homepage
    Q: So why aren't we doing it? Why aren't we making this priority 1, when it could boost space exploration by several orders of magnitude?
    A: Because today's gov and NASA contractors still have a lot of expensive rocketry missions in store, to extract lots of funding from the taxpayer. The mechanism is identical to there being no alternative to gas-powered cars, because influential people have a lot to loose when new concepts make things cheaper! So they keep telling you it can't be done, and it CAN'T be done until someone actually does it!

    If you would do a poll now asking the average American whether a space elevator could be done, I'm willing to bet a month's salary that the result will be: "90% think it's a ridiculous idea and it can never be done." and answers like "That's all science fiction, we better stick to our rockets, and by the way spacefaring is very complex it can't be done just by stepping into an elevator."

    That's because of the way the public opinion works. If NASA would announce tomorrow "we are, as of now, committing a large part of our budget to build a speca elevator" you can bet that wise people keep appearing from all over the place, explaining the Reasonable Concept Of The Space Elevator And Why It Must Be Built.

    But that won't happen any time soon. Sometimes I think science fiction may have done more to prevent space exploration progress than many other factors, because it's so easy to use it to ridicule concepts of technological progress.

    It makes me so sad when I see what we could achieve even within our lifetime, but our world's inherent corruption prevents it from becoming a reality... (sniff)
    • by malakai (136531) on Thursday March 06, 2003 @03:32PM (#5451419) Journal
      We're not doing it now because the tech isn't yet ready. Certain aspects of the nano-tubes tech has been seen to work in a lab, but it's not at a production level by any measure.

      NASA should be commended for giving grants to do this research (twice), event though NASA and the government should NOT be the ones who build this.

      If you would do a poll now asking the average American whether a space elevator could be done, I'm willing to bet a month's salary that the result will be: "90% think it's a ridiculous idea and it can never be done." and answers like "That's all science fiction, we better stick to our rockets, and by the way spacefaring is very complex it can't be done just by stepping into an elevator."
      Keep your $1,700 bucks and keep your ridiculous satistical assumptions based on your view of your little world. They don't help us here. Quit trying to find reasons to blame others.

      Because today's gov and NASA contractors still have a lot of expensive rocketry missions in store
      And thats still usefull, a space elevator isn't going to get us to the Mars without some other propulsion. And I'd HATE to see all projects put on hold while we wait for the new Space Elevator to be developed, which will take 15-20 years with cost/project overruns. Everyone keep doing what your doing and if the Space elevator pans out we'll be even better off.

      It makes me so sad when I see what we could achieve even within our lifetime, but our world's inherent corruption prevents it from becoming a reality...
      Get off your ass, out of your parents basement, and DO IT. Try, aim, shoot, whatever it is go for it. Others [armadilloaerospace.com] have, why not you? Don't think you have the cash? Raise some. Don't have the talent? Read books. Go back to school. Go to school for the first time, just stop whining about how it's everyone elses fault (and those dumb "John Q Public" people) that you aren't out conquering some new solar system in your kilrathi fighter....

      -Malakai
  • Less lightning? (Score:3, Interesting)

    by Anonymous Coward on Thursday March 06, 2003 @12:54PM (#5449710)
    Because you'd have a conductor between the clouds and the ground, it should equalize the charge differences and would prevent the "shadow" charge from being generated on the ground which would prevent the path of negative charge from the cloud to generate the "equalization" bolt of lightning.

    Assuming that the current theories on how lightning is created are accurate, I wonder if the localized decrease in lightning would have any environment effects.
  • by jqh1 (212455) on Thursday March 06, 2003 @01:02PM (#5449814) Homepage
    One can't help but be reminded of the biblical Tower of Babel (a proposed tower that would reach heaven) -- you'll remember that God put the ax to that project by mixing up the languages spoken by the various participants.

    Now, if NASA is involved, will the mixup be metric versus imperial measurement? :)

  • by argStyopa (232550) on Thursday March 06, 2003 @01:08PM (#5449886) Journal
    Why is everyone saying "NASA should do this!" or "the government should do this!".

    If I had several billion dollars, I would be a complete idiot NOT to sink my money into such a venture. Of course, /.ers would be immediately suspicious of the "Bill Gates Space Elevator", and it would frequently lock up and need rebooting.

    For the mega-rich, the income potential and (maybe more importantly) the "my name in human history" potential of this SHOULD be irresistible. Plus, I'm a firm believer in free-enterprise. Let companies do it for a profit and it will be safer, quicker, and more efficiently run than any government project.
  • by tmortn (630092) on Thursday March 06, 2003 @01:24PM (#5450038) Homepage
    But couple of issues.

    50,000 miles is a long way for a mechanical crawler. Escpecially one that amounts to a 20 tonne capacity elevator and it could never exert more than the load limit in terms of force.. IE if 20 tonnes is the theoretical maximum for the 130 rated nano tubes then lifting 20 tonnes at say a 9.8 mps (1G) acceleration would be roughly 40 tonnes of force on the cable meaning a broken cable. Thus you would likely be lifting 18 tonnes and having low acceleration loads, you also could not exceed that load when decelerating. Hitting the gas or breaks to hard could lead to exceeding the cables strength. I am wondering if a lighter system with more leeway to zip up and down the cable would not allow for easier and more timely transfer of mass.

    for example:

    If you can accelerate/decelerate at 1g with a 20 tonne vehicle (40 tonnes of force ) then you can accelerate at 4g's with a 10 tonne vehicle ( also 40 tonnes of force ). This means you can go ~4 times as fast which is a very significant difference when dealing with long transit distances. So a 20 day round trip by the 20 tonne could be accopmlished in 5 days by the ten tonne and would allow for 4 trips in the same time. Even if the 10 tonne only had 30% of the cargo capactiy it lifts more in the same amount of time over the long haul. You get that benifit whatever the units of acceleation are be it G or more likely in fractional G acceleration loads. And the smaller the rates we are dealing with the larger the impact is of relatively small increases.

    Don't get me wrong, the idea is great but the margin of error here sounds awfully thin esepcially considering the key material hasn't reached its theoretical proving point in a LAB much less in a mass production environment. Once they do that I say full steam ahead. But until then its a bit premature to start tossing out headlines reading "Space elevator for just 6 billion "

    perhaps if it read
    "Space elevator for just 6 billion IF IF IF IF IF IF IF IF IF"

    • If you can accelerate/decelerate at 1g with a 20 tonne vehicle (40 tonnes of force ) then you can accelerate at 4g's with a 10 tonne vehicle ( also 40 tonnes of force ). This means you can go ~4 times as fast which is a very significant difference when dealing with long transit distances.

      The thing is, all the space elevator concepts I've seen have put the crawler in physical contact with the cable. There are limits on maximum speed imposed by the mechanical strength of all the other components--not just the cable. Realistically, I would expect an acceleration relative to the cable of maybe a tenth of a gee for the first and last three minutes of the trip.

      That results in a cruising speed of over six hundred kilometers per hour (better than 400 mph in the United States) and climbs the cable in a little less than four days. If the maximum acceleration were limited to 0.01 g, the acceleration phase would last a full half hour--but the whole trip would be lengthened by only about three percent.

      If the vehicle actually were to accelerate (at 0.1 g) for the entire journey, at the halfway point the top speed would be a hellish 25000 km/h--a little hard on your crawler wheels and bearings, even though the trip would only be four hours long.

      That said, if the cable had a 20 ton breaking tension (estimated), I probably wouldn't ever put more than a two or three ton load on it. I could jerk a crawler through a five gee mishap and not have to worry. (Actually, one wonders how much the nanotubes can stretch longitudinally before failing. Can we get away with large transient loads that get soaked up by the cable stretching?) For the first few years, I'd want most of the payloads going up to be more nanotubes, leading ultimately to several parallel ribbons--and crawler tracks.

  • the stuff of memes (Score:4, Insightful)

    by Un pobre guey (593801) on Thursday March 06, 2003 @02:13PM (#5450537) Homepage
    • For the mega-rich, the income potential and (maybe more importantly) the "my name in human history" potential of this SHOULD be irresistible.
    • Plus, I'm a firm believer in free-enterprise. Let companies do it for a profit and it will be safer, quicker, and more efficiently run than any government project.
    • The good reason to reach for this which can't be emphasized enough in the current environment is that for a relatively modest investment, the impact on the economy would be enormous (and good). Compared to other proposals to jumpstart the economy, this one has incredible bang for the buck.
    • I am sure the terrorist strikes will stop themselves if the US gains a reputation for a R&D and science nation instead of a warring and military nation.
    • I seem to recall that the base of these things would be on large platforms anchored in the middle of the ocean, so if they did collapse, they would just fall harmlessly over water.
    • Space elevators around Mars create an efficient Earth-Mars transportation network. Elevators on the moons of Jupiter throw spacecraft down into Jupiter's turbulent upper atmosphere to scoop up 3HE and ship it back to Earth in decade-long space convoys where it will power the latest and greatest IEF fusion power-plants.
    Meme 1: Cheap access to orbit will translate into a vast economic bounty.

    Meme 2: Big infrastructure projects are done better, faster, and more cheaply by private enterprise than by government commission.

    Meme 3: Terrorism will stop if we only [insert good-intentioned but simplistic solution here]

    Meme 4: If a space elevator falls, nothing bad will happen. It's way out in the middle of the ocean.

    Meme 5: [insert currently fashionable incarnation here] nuclear fusion is the way to go.

    Meme 6: Your "place in human history" is really really important.

    Meme 7: Mining the solar system is not only economically feasible, it's commercially attractive.

    I have a hard time with all of these, although I'm sure circumstances can be described where they have a kernel of truth in them.

    As I have mentioned in the past, I am in favor of a major unmanned space program, but mainly as a vehicle to stimulate technological development with non-military aerospace and robotics projects. The Space Elevator might help, if it fulfills its promise of cheap access to LEO. Hard to believe, though. 10 years and 6 billion dollars seems very optimistic.

Things are not as simple as they seems at first. - Edward Thorp

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