Space Towers

Long ago kings and empires often signaled their power via impressive buildings, such as temples, cathedrals, and pyramids.   Today, cities and corporations often similarly signal via big skyscrapers, bridges, and ships.  But for nations, the fraction of  wealth spent on a single showy construction has dramatically decreased.  Space programs serve a similar function, but don’t leave such huge monuments to admire.

A new Acta Astronautica article suggests this trend may reverse.  New Scientist reports:

A giant inflatable tower could carry people to the edge of space without the need for a rocket, and could be completed much sooner than a cable-based space elevator, its proponents claim. … The team envisages assembling the structure from a series of modules constructed from Kevlar-polyethylene composite tubes made rigid by inflating them with a lightweight gas such as helium.

To test the idea, they built a 7-metre scale model made up of six modules.  … The team [also mathematically] modelled a 15-kilometre tower made up of 100 modules, each one 150 metres tall and 230 metres in diameter, built from inflatable tubes 2 metres across. Quine estimates it would weigh about 800,000 tonnes when pressurised – around twice the weight of the world’s largest supertanker. “Twenty kilometres up is about as dark as outer space. You can see about 600 kilometres in any direction.”

The analysis in the tech paper is solid, if preliminary.  This seems doable now. (Quotes from the paper are below.) My immediate reaction was tech lust and pride: “COOL!”  Once upon a time I would have celebrated the social value of such innovations, but now I understand that while innovation in general should be praised, we probably waste too much on showy but not especially useful monuments like this.

Yes, it could be used for tourism, to reduce the cost of spaceflight, and for geoengineering, but those probably won’t cover its costs.  I’m proud my culture seems able to do such a thing, but I’ll admit my gain may come at the expense of others who look worse by comparison.  Those quotes from the paper:

We propose an alternative device to provide access to the near space and space environments that utilizes a self-supporting core structure. The structure provides a fixed link between ground and near space locations enabling the transportation of equipment, personnel and other objects or people to platforms or pods above the surface of the Earth for the purpose of scientific research, communications and tourism. The device may be assembled from the surface upwards, avoiding difficult and expensive in-orbit construction. The space-elevator tower can provide access to lower altitude regions and can also be scaled to access altitudes above 15 km, or the typical ceiling altitude for commercial aviation. The approach may be further scaled to provide direct access to altitudes above 200 km and with the gravitation potential of Low Earth Orbit without the technical challenges associated with constructing a cable at least 35,000 km long. The elevator platforms also have significant advantages over orbiting satellite platforms. Geographically fixed but providing access to regions of space closer to the surface than geostationary orbit, elevator platforms provide the ideal means to communicate over a wide area and to conduct remote sensing and tourism activities. As a tourist destination, the elevator platforms provide stations located at fixed attitudes from the surface for observation. The elevator platforms provide the means to access safely a region of space with a view extending hundreds of kilometers. …

Consider an example core-structure design for an Earth-based elevator to access near space at 20 km altitude. Advantageously, to access orbit, the elevator could be constructed at 5 km altitude in one of four regions on the equator. The core would be required to span a further 15 km altitude. Based on Elevator B, a suitable structure comprises of gas cells with constant wall thickness 1.2 cm arranged in a torus of inner diameter 228 m and outer diameter 230 m. Fabricated from Boron, a 15 km elevator structure can be supported by 150 bar hydrogen gas. Approximating the structure as two concentric cylinders, the mass of the structure is 6.5×10^8kg, and the mass of the pressurization gas needed is 1.4×10^8kg. Other core designs may be analyzed by comparison with the two-cylinder design and by appropriate adjustment for the amount of wall material utilized.

Constructed at 5 km altitude, the structure would have a buoyant mass of 3.1×10^6kg giving a total mass of 7.8×10^8kg. The load capacity of the structure, in excess of that needed to support itself, is 3.1×10^8kg of force equivalent. The critical buckling load at the top is 4.1×10^9N, and at the center of gravity (located at 7.3 km up the core) the critical load is 1.6×10^9N, which exceeds significantly the dead weight load of the building, including the mass of the gas, indicating that the core would be structurally stable and able to support the raising of payloads of mass in excess of 10^6 kg. By further tapering the wall thickness, further design margin may be obtained by lowering the center of gravity and reducing the structural mass, or taller structures may be constructed. Alternatively, the core diameters can be tapered to increase the structural stiffness in the base, although the variation of core diameter may be undesirable for mounting elevator machinery. Additionally, the core can be segmented and pressurized equivalently without inducing an imbalance of support forces between segment walls. …

Consider a highly simplified scenario where a single stage-to-orbit rocket is launched to a typical circular orbital height of 120 km. … Comparing initial to final rocket-mass ratios, the elevator launch at 20 km is shown to be 26% more efficient than the equivalent ground launch.

Added 13June: If you search for “Space Tower” you’ll see Alexander Bolonkin has published over a half dozen times (eg 1 2 3) on inflatable space towers since 2002.  But the Acta Astronautica article doesn’t cite him at all.  Suspicious.

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  • John Maxwell IV

    Maybe this is stupid, but for years I’ve thought that space travel was an extremely worthwhile investment. It doesn’t seem like a good idea for humanity to have all its eggs on one planet.

  • Hal Finney

    There’s not much difference in gravity at 200km versus at the surface. Earth’s radius is 6370 km so going out to 6570 km only nets you about a 6% reduction in gravity. It would make a heck of a broadcast tower though.

  • http://hanson.gmu.edu Robin Hanson

    Hal, I added to the quote from the paper on the increased efficiency of space launches.

    John, no space tech fielded anytime soon will have any effect on our number of baskets, since humanity isn’t remotely capable of living independently of Earth.

    • http://transhumangoodness.blogspot.com/ Roko

      > John, no space tech fielded anytime soon will have any effect on our number of baskets, since humanity isn’t remotely capable of living independently of Earth.

      Let us define the time at which the human race stands a 50% chance of survival given the total destruction of the planet earth as t_survival. If no technological singularity occurs, it wouldn’t be unreasonable to say t_survival will be in more than 40 years but less than 300 years.

      Really cheap access to space via a space tower would make it economically viable for companies to do various things in space and for an entire space economy to develop. This would accelerate the development of a multitude of effective strategies for surviving and thriving in space, and for doing it cheaply. This process is likely to be auto-catalytic – space access costs will come down further as more people want to go there (economies of scale). Furthermore, a *community* of space enthusiasts – people who are prepared to take huge risks to live in space, but who feel compensated for those risks by the psychological benefit it gives them – may develop.

      t_survival is thus likely to come forward if we make “mass space” come sooner.

      How much is advancing t_survival by one year worth? By my standards, rather a lot; I’m not sure how to put a dollar figure on the future of the entire universe.

      • http://transhumangoodness.blogspot.com/ Roko

        However I should add that a 20km space tower doesn’t make it much cheaper to get into space. I’m no expert, but I expect that the only good application would be in conjuction with a Tether propulsion system

      • http://transhumangoodness.blogspot.com/ Roko

        “Consider a highly simplified scenario where a single stage-to-orbit rocket is launched to a typical circular orbital height of 120 km. … Comparing initial to final rocket-mass ratios, the elevator launch at 20 km is shown to be 26% more efficient than the equivalent ground launch.”

        – right, this is not a sufficiently compelling difference.

      • http://hanson.gmu.edu Robin Hanson

        We aren’t remotely close enough to a low enough cost of getting into space to kick off a substantial space economy. So the best way to get to that point is to simply grow the world economy; investments now in space activities that don’t pay their way hinders that goal.

      • http://transhumangoodness.blogspot.com/ Roko

        > We aren’t remotely close enough to a low enough cost of getting into space to kick off a substantial space economy. So the best way to get to that point is to simply grow the world economy; investments now in space activities that don’t pay their way hinders that goal.

        What $ per kilogram to orbit do you think we need to get to?

      • John Maxwell IV

        >We aren’t remotely close enough to a low enough cost of getting into space to kick off a substantial space economy. So the best way to get to that point is to simply grow the world economy; investments now in space activities that don’t pay their way hinders that goal.

        OK, I’ll tentatively take your word for this because you’re an economist. But I’ve got a question: does the sector of the economy matter? If video game sales go up does that help spaceflight?

        It seems to me that this question is quite complicated. Another aspect of things is how reasonable the assumption that man-hours convert into research results at a constant rate is.

      • Nick Tarleton

        What likely risks can you think of that space colonies would be safe against, but sealed deep mines on Earth wouldn’t?

      • John Maxwell IV

        >What likely risks can you think of that space colonies would be safe against, but sealed deep mines on Earth wouldn’t?

        That’s a good point. I suppose that sealed deep mines could use geothermal energy. But you might be stuck in the mine for a while in the event of a catastrophe.

        Do you know of anyone working on the problem of surviving a long time in a sealed deep mine?

  • http://ssmag.wordpress.com Science in Society

    Still, this sort of thing would work in that directions, not least by developing better manned spaceflight technologies.

  • http://blog.efnx.com Schell

    The next worthwhile signaling of a civilizations power should be the successful deployment of a self sustaining colony of robots on the moon. That’s a pretty big step towards getting our eggs out of this basket.

  • nick

    I have written about oversized technologies as symbols of national glory and decadence, and to what extent they might have long-term (dis)utility for tackling a frontier, in my article How to Succeed or Fail on a Frontier.

    Robin: no space tech fielded anytime soon will have any effect on our number of baskets, since humanity isn’t remotely capable of living independently of Earth.

    Schell: …a self sustaining colony of robots on the moon. That’s a pretty big step towards getting our eggs out of this basket.

    Robin is right here and what Schell describes is an industrial fantasy, even if there were enough hydrogen, carbon, nitrogen, and other important volatiles on the Moon to provide the many fluids and materials containing those elements that such an industrial infrastructure would need. I describe why in my article Polynesians vs. Adam Smith.

    • http://hanson.gmu.edu Robin Hanson

      Those are both good articles.

  • andrew c

    Self sustaining moon robots – COOL!!!

  • CannibalSmith

    What’s the cost of the tower?

  • http://timtyler.org/ Tim Tyler

    “To stay upright and withstand winds, full-scale structures would require gyroscopes and active stabilisation systems in each module.”

    Hah! – very funny.

  • http://hanson.gmu.edu Robin Hanson

    I just added to the post.

  • Jay

    As a chemist, I see a serious flaw in this proposal. Mainly, it requires a lot of helium. Since Earth’s gravity doesn’t capture helium, we have a very limited quantity available on Earth. Helium also diffuses rather quickly through many materials (you may have noticed that helium balloons tend to shrink in a few days), so constant replenishment would be needed. I haven’t done the math (and couldn’t, without estimates of the surface area, thickness, and relevant helium diffusion constants of the materials of choice), but I seriously doubt that this is a practical proposal.

  • http://www.ciphergoth.org/ Paul Crowley

    Such launch devices will pay their way in reducing existential risk if they can reduce the cost of global warming mitigation strategies like the Angel fleet.

  • http://timtyler.org/ Tim Tyler

    More uncritical coverage:

    http://scienceblogs.com/principles/2009/06/inflatable_space_elevator_eh.php

    To reiterate, the idea makes no sense, because of the wind.

  • anon

    As a chemist, I see a serious flaw in this proposal. Mainly, it requires a lot of helium. Since Earth’s gravity doesn’t capture helium, we have a very limited quantity available on Earth.

    We can harvest some helium from the Sun. Yes, it’s quite hot, but we’d go there at night time.