Astronomy Without A Telescope – Space Towers

by Steve Nerlich on September 4, 2010

The Seattle space needle pokes through the cloud tops (well, just fog really… it's only 184 meters high). Credit: Liem Bahneman, pixduas.com

Arthur C Clarke allegedly said that the space elevator would be built fifty years after people stopped laughing. The first space tower though… well, that might need a hundred years. The idea of raising a structure from the ground up to 100 kilometers in height seems more than a bit implausible by today’s engineering standards, given that we are yet to build anything that is more than one kilometer in height. The idea that we could build something up to geosynchronous orbit at 36,000 kilometers in height is just plain LOL… isn’t it?

Space tower proponents point to a key problem with the space elevator design. It may only be after we have spent years inventing a method to manufacture 36,000 kilometers of flawless carbon or boron nanotube fiber – which is light enough not to break under its own weight, but still strong enough to lift an elevator cabin – that we suddenly realize that we still have to get power to the cabin’s lifting engine. And doesn’t that just mean adding 36,000 kilometers of conventional (and heavy) electrical cable to the construction?

Mind you, building a space tower brings its own challenges. It’s estimated that a steel tower, containing an elevator and cabling, of 100 kilometers height needs a cross-sectional base that is a 100 times greater than its apex and a mass that is 135 times greater than its payload (which might be a viewing platform for tourists).

A solid construction capable of holding up a launch platform at 36,000 kilometers altitude might need a tower with ten million times the mass of its payload – with a cross-sectional base covering the area of, say, Spain. And the only construction material likely to withstand the stresses involved would be industrial diamond.

A more economical approach, though no less ambitious or LOL-inducing, are centrifugal and kinetic towers. These are structures that can potentially exceed a height of 100 kilometers, support an appreciable mass at their apex and still maintain structural stability – by virtue of a rapidly rotating loop of cable which not only supports its own weight, but generates lift through centrifugal force. The rotation of the cable loop is driven by a ground-based engine, which can also drive a separate elevator cable to lift courageous tourists. Gaining altitudes of 36,000 kilometers is suggested to be achievable by staged constructions and lighter materials. But, it might be sensible to first see if this grand design on paper can translate to a proposed four kilometer test tower – and then take it from there.

There are also inflatable space towers, proposed to be capable of achieving heights of 3 kilometers with hot air, 30 kilometers with helium or even 100 kilometers with hydrogen (oh, the humanity). Allegedly, a 36,000 kilometer tower might be achievable if filled with electron gas. This is a curious substance argued to be capable of exerting different inflationary pressures depending on the charge applied to the thin-film membrane which contains it. This would allow a structure to withstand differential stresses – where, in a highly charged state, the highly excited electron gas mimics a molecular gas under high pressure, but with a reduced charge it exerts less pressure and the structure containing it becomes more flexible – although, in either case, the overall mass of the gas remains unchanged and suitably low. Hmmm…

An inflatable 100 kilometer high, 300 kilometer long space pier, built to launch spacecraft horizontally. Humans might survive the G forces required to achieve orbit - which they certainly wouldn't do if the same trajectory was attempted from sea-level. Credit: Josh Hall, autogeny.org/tower/tower.html

If this all seems a bit implausible, there’s always the proposed 100 kilometer high space pier that would enable horizontal space launch without rocketry – perhaps via a giant rail gun, or some other similarly theoretical device that works just fine on paper.

Further reading: Krinker, M. (2010) Review of new concepts, ideas and innovations in space towers. (Have to say this review reads like a cut and paste job from a number of not-very-well-translated-from-Russian articles – but the diagrams are, if not plausible, at least comprehensible).

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  • IVAN3MAN_AT_LARGE

    Interesting article, Steve, but one minor nitpick…

    At the fourth paragraph, in the third line, “like” should be likely. :-)

    N.B. If anyone has a problem with the term “centrifugal force”, then click here. ;-)

  • http://www.cheapastro.com Steve Nerlich

    @ IVAN3MAN_AT_LARGE
    Thanks, typos are more than likely from this writer.

    Acknowledged that centrifugal is a psuedo-force, although it’s not the same as the centripetal force (as is kind of implied by the cartoon). If you are thrown against a wall – that’s either padded or brick – the brick wall collision hurts a lot more, even if the throwing force was the same.

    It’s useful to have a shorthand term for ‘the reactive force that counters centripetal force’ – i.e. centrifugal.

  • HeadAroundU

    Yeah, let’s build it for the LULZ! :d

  • http://www.dvefx.com damian

    Why bother tethering it to the ground. ? String a few hundred balloons together as a high altitude platform in near space and then use a rail gun as a launch platform. The platform itself can itself be traveling at speed and assist launches. Of course you still need to be able to ferry materials up to the platform, and that would require aircraft that can (catch up). I wonder if its even possible to land a 747 @ altitude. :)

  • http://www.dvefx.com damian

    Actually, A plane would not have to land, Just dock At speed. Transfer cargo and separate. Each dock would actually help (push) the platform.

    BTW, the new website design sucks, comments have weird lines through the text and every posts comes up with a Node Unavailable message.

  • IVAN3MAN_AT_LARGE

    @ STEVE NERLICH,

    Actually, I agree with the bad guy in that cartoon, and also with Dr. Phil Plait: “When I say centrifugal, I mean centrifugal!” :-)

    @ DAMIAN,

    I also complained about those two website issues; Nancy said that they are “working on it”!

  • http://sputnikage.com nafis

    Hey, I looked at the source code for the comments, and the line problem is pretty easy to fix.

    You need to edit comments.php (if it exists) and add:

    to the end of the

  • http://sputnikage.com nafis

    uhh.. sorry forgot that you can post html to comments…

    I can fix your comments problem for free, please email me

  • jimhenson

    the cloud minders in star trek confined the masses all poorly paid workers to live on the surface in underground mines. Maybe the corilous force that causes water to rotate clockwise or counterclockwise depending on earths latitude and location away from the equatoral rotation plane, could support these kinds of structures?

  • http://www.cheapastro.com Steve Nerlich

    @ At Damian and others
    You say – why bother tethering it to the ground? These one hundred kilometer high structures are not tethers, but ladders. The majority of energy expended by current rocketry involves getting from sea level up to an altitude of one hundred kilometers. The first stage of the Saturn V only managed to launch an Apollo mission up to 70 kilometers altitude, although the first stage was over one third (2.3 million kg) of the total mass of the launch vehicle.

    @ anyone
    I understand a website upgrade/fix is close. Mind you, I do like how most of the related posts to my articles are written by me. I hope they don’t fix that :-)

  • http://www.dvefx.com damian

    We know that Helium Balloons could get halfway there (about 50km up). The Max altitude for an average 747 is some 10 km. So an orbital platform would have to be altitude maneuverable, dropping down to under 10 km for Cargo delivered by regular aircraft and then gaining max altitude for orbital launch. Use hydrogen gas as part of the platform for fuel. (Cryogenic storage should be much easier at altitude, although @ 50km up it can be a balmy -3 Celsius due to temperature inversion)

    Its my understanding that once your close to 80km up you can start to use ion propulsion. (GOCE satellite as example). If you have Delta V. (Mach 3 to 5)

    I do admit its not pretty, but it can be done with todays technology, and as you mention Steve, 1/3 of the weight of the Saturn V was to get it 70KM up. @ 50Km with the help of centrifugal force (I think the platform could easily get up to speeds of 500km per/h) your lifting more useful mass into space then just fuel.

    Of course you still have to get your spacecraft up to escape velocity so rockets aren’t dead yet, but the costs should be far lower. Isn’t this essentially what Branson is doing with the the two plane Virgin Galactic system?.

    The tethered idea is great, but this is something potentially achievable now. Besides a low earth platform has many science applications, not just launch.

    :) Sunday Musing are fun.

    Damian

  • Aqua

    I think what’s needed here is a “Baseline Assisted Ballistic Electromagnetic Launcher”, IF I get the ‘space pier’ concept right?

    The ‘base’ connecting to the Earth being a tower… or The tower of BABEL? And you KNOW what happened in THAT story? The ‘Sky People’ were not pleased with our efforts and tore that building down!

  • Lawrence B. Crowell

    Your only prospect for this, and I think it is extremely remote at that, or for building anything like a space elevator is to build from space down. I think you will have to catch a near Earth asteroid, attack an ion propulsion system to the thing and slowly push it so you can park it in geosynch. From there you use the materials in the asteroid to build your elevator from space down to Earth, meanwhile also building up the counter weight beyond geosynch. It does not take much physical or engineering sense to think on why building up will never work.

    LC

  • Bravehart

    Can we not wait a while longer?
    Untill we have solved the anti gravity issue?
    If we can nuetralize gravity by creating a force field, we do not need space elevators. It works similar to levitation rail transport. This will cost a lot less to get in
    orbit?

  • IVAN3MAN_AT_LARGE

    LAWRENCE B. CROWELL:

    I think you will have to catch a near Earth asteroid, attack [sic] an ion propulsion system to the thing and slowly push it so you can park it in geosynch.

    The problem with that is the low thrust of ion propulsion systems, when compared with chemical or nuclear rockets.

    Also, I think that you had meant to say attach there, not “attack”. ;-)

  • IVAN3MAN_AT_LARGE

    Damn it! I forgot to close the bold tag after “attach”. Sorry about that. :|

  • http://spaceshaft.org Nelson Semino

    Many comments here (especially those from Damian) make a very good description of a SpaceShaft. What is missing is the fact that a SpaceShaft is not only a tower/scaffolding system but also a unidirectional elevator system.

    A SpaceShaft is a hybrid system because the whole structure of buoyant building blocks is levitated with new building blocks insertions at the base and so the top ones (@ > 50 km of altitude get jacked-up further into space thanks to the buoyancy below.

    A building using this method of construction, with a diameter of 100 m will have a gross upthrust 5000 tonnes at the Karman line. From the summit of the structure “free-ride” assisted launches of spacecraft/spaceplanes is possible with economical fuel consumption, with the benefit of the mobility that rockets offer.

    Since reaching beyond the Karman line is possible thanks to the potential energy, structures intended to into space will need to be constructed with space-grade materials since regular plastics, (like Mylar on its own are not suitable,) will need to be engineered.

    Such structures could be built also anywhere, not just at the Equator since they employ mooring/guy lines pretty much like tall telecom antennae.

    More info visit http://spaceshaft.org

  • Torbjorn Larsson OM

    Untill we have solved the anti gravity issue?

    Because anti-gravity is like time-travel: it can’t happen, for fundamental reasons of physics.

    Gravitation isn’t a force, where you can have equal but opposite charges from a field. Say, in electromagnetism. There like charges repel, unlike charges attract, and in your picture one could be chosen to be the “anti” interaction.

    Gravity is curvature of space-time (which can be approximated as a force in many cases, and indeed is thought to have one charge, gravitons). How would you “anti-curve” space-time?

    FWIW, you _can_ lower a gravitational relative energy, locally straighten out a curved space, simply put another Earth close to ours with “some” diamond pillars in between. (So you use the same force to set up your “anti”- picture.) But that would only get you Earth-”Earth” cheap travel.

  • http://www.cheapastro.com Steve Nerlich

    @ anyone

    I thought someone might comment on the issue of powering the space elevator cabin – which strikes me as a non-trivial problem for space elevator design. Is the answer to have a 72,000 km nanotubule loop and a ground based engine that draws the loop around – while the cabin (perhaps with battery power for light and heating) is just passively fixed to the loop?

  • Lawrence B. Crowell

    The problem with anti-gravity is similar to why warp drives and time machines are not likely possible. The problem is that anti-gravity violates the Hawking-Penrose energy conditions. The most general energy condition is the averaged weak energy condition. This is that the 0-0 or time-time component of the momentum-energy tensor must be positive. This component is energy density, and if it is equal to zero or positive it guarantees the curvature of spacetime is such that paths in spacetime focus towards each other on average. For instance a cloud of particles around the earth will fall towards Earth and in a spacetime sense their paths focus into each other. This also means the curvature of spacetime is positive, or that it curves so that any circle in that space (spacetime) there is less space enclosed than one would expect from the formula Area = 4pi R^2. In a finite element language, a flat circle with a disk has a wedge cut out of it and the wedge closed up by gluing the wedge up. This gives a little cone, and if we then “smooth that out,” since a cone as a singularity at its point, this is an example of positive curvature.

    If the energy density is negative, this defocuses geodesics. This gives the meaning of anti-gravity already, for it involves the repulsive motion of particles. This is needed for wormholes, where a thin layer just above where the event horizon of a black hole has this exotic matter. This defocuses geodesics, but requires this defocusing to occur on an opening topologically connected to this first opening that appears similar to a black hole. The Alcubierre warp drive solution also requires this negative energy. This involves negative curvature of space or spacetime. In the finite element example above, we may make the cut of a flat disk to its center, but instead of cutting out a wedge we take a wedge and glue it in there. This amounts to inserting “more space” into the disk, which creates instead of a cone a saddle shape.

    So all we have to do to get anti-gravity is to get this exotic matter, some sort of quantum field, and employ it in various ways. To solve the problem of anti-gravity amounts to solving the problem of faster than light and wormholes and even time travel. So what is the problem? The violation of the averaged weak energy condition means there is not lower bound on the quantum spectrum of this exotic quantum field. The Hawking-Penrose averaged weak energy condition is equivalent to saying there is some lower bound on the energy levels of the field. This fact is what solved the hydrogen atom catastrophe predicted by classical mechanics. A charged particle, such as an electron, that is accelerated will emit radiation and lose energy. The nucleus of the atom has a potential V = -ke/r (k = constant) and so the inspiral of the electron will produce an infinite amount of radiation. Quantum mechanics then comes in to produce a discrete set of energy levels with a minimal energy level at the bottom — the S-shell. This fact persists in all quantum systems.

    I could go into considerable depth here, for quantum mechanics is a sort of logical framework. The Bell theorem or the violation of classical inequalities is a sort of logical apparatus to nature. Spacetime physics appears to respect the same logic, and I wrote a paper 20 years ago on how quantum theory and general relativity, within admittedly a restricted setting, have underlying equivalent Galois field extensions. The two are in some sense fundamentally the same thing, but under different categorical maps.

    So to conclude it seems highly unlikely we will derive anti-gravity machines. For those who crave the opening of the space frontier this is unwelcome news, but unfortunately this is how the cards read.

    LC

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