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posted by Fnord666 on Tuesday September 04 2018, @01:04PM   Printer-friendly
from the going-up! dept.

Japan is taking us one step closer to a space elevator.

Elon Musk may not believe in space elevators yet, but Japan is taking a step forward to realise the dream of travelling to space by elevators instead of the traditional rocket.

A team of researchers from Japan's Shizuoka University and other institutions will conduct the first test in space this month as part of a project to build a space elevator, Japan's The Mainichi reported last week. The space elevator essentially ferries people and cargo shipments in an elevator car travelling on a cable connecting Earth to a space station.

This test is the first exploring the movement of a container on a cable in space. Two ultra-small cubic satellites measuring 10 centimeters on each side connected by a steel cable about 10 metres long will be carried from Kagoshima's Tanegashima Space Center to the International Space Station on Sept. 11.

From there, the connected satellites will be launched and a motorised container acting as an elevator car will travel along the cable and have its journey recorded via a camera attached to the satellites.

The project's technical advisor, Japan's construction giant Obayashi Corporation, is also working on a similar project, though it previously said it expects to deliver a space elevator by 2050.

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  • (Score: 3, Informative) by Immerman on Tuesday September 04 2018, @06:36PM (2 children)

    by Immerman (3985) on Tuesday September 04 2018, @06:36PM (#730394)

    Keep in mind that the cable is NOT going to be uniform thickness - instead it's cross section will increase... geometrically? exponentially? with height. I don't recall exactly - but much faster than linearly. The lowest section only has to be thick enough to safely support the maximum payload.

    Lets call the cross-section area at that point A, required to support a mass of M. Now, some length up the cable, let's call it L, the mass of the cable below that point equals the mass of the payload. So at that point the cable needs to have a cross-sectional area of 2A, and thus twice the mass. Another length L above that the cable will need to support the payload, plus the first length of A cable, plus the second length of 2A cable, for a total mass of 4M, requiring the cable to have a cross-section of 4A. So the pattern is:

    Height -- cross-sectional area -- Mass suspended below that point
      0 -- A -- M
      L -- 2A -- M + M
    2L -- 4A -- M + M + 2M
    3L -- 8A -- M + M + 2M + 4M
    4L -- 16A -- M + M + 2M + 4M + 8M
    So, looks exponential in my oversimplified discrete sample estimate - might look better in a continuous analysis, but you get the idea

    Trying to maintain a constant cross-sectional area would push the cable well beyond the limits of existing materials, even carbon nanotubes are only barely feasible with the exponential thickening, and that with basically no safety margins. The better the strength-to-weight ratio of the material the slower the thickening, and carbon nanotubes look to be about as good as is physically possible. Something less impresssive, like high tension steel? The exponential growth of the cross-sectional area with height reaches the point of completely encasing the planet long before it reaches geostationary orbit.

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  • (Score: 2) by c0lo on Tuesday September 04 2018, @07:40PM (1 child)

    by c0lo (156) Subscriber Badge on Tuesday September 04 2018, @07:40PM (#730419) Journal

    The lowest section only has to be thick enough to safely support the maximum payload.

    Not gonna cut it. Rationale - the cable isn't going to sit in balance without a tension, the equilibrium is unstable, any perturbation is subject to positive feedback. And gosh, those cyclones/hurricanes/typhoons just can't wait to provide some perturbations.

    Besides, I suspect the cable is going to need some controlled oscillations, be it only to get some hundred metres out of the way of some satellites or near-earth asteroids now and then. Too risky to control those oscillations without tethering one end.

    So, looks exponential

    Interesting, never thought about. But won't be a single exponential... Need to grow exponential up to geostationary (where the cable tension is max) then it can decrease exponentially to the distal end.

    • (Score: 2) by Immerman on Wednesday September 05 2018, @01:42PM

      by Immerman (3985) on Wednesday September 05 2018, @01:42PM (#730749)

      Yes, cyclones, hurricanes, etc. are going to provide some pertubations - quite possibly terminal ones. That's why most plans have the base of the beanstalk well inland and atop a high mountain - up above the worst of atmospheric disruptions. For maximum reliability you wouldn't want it to touch the ground at all - if it simply stops 40 or 50 miles above ground any hurricanes, etc. will simply pass harmlessly beneath it. Of course that means you'll have to take a high-altitude capable aircraft up to the base, which makes it a bit less convenient. On the other hand, that would also let you get a bit out of geostationary, so that the bottom end could slowly sweep across the globe to serve a much greater area,albeit only periodically.

      And yes, it's only exponential up to geostationary, which is the point of maximum tension. As to whether it extends much beyond that - it might, it would come in handy as a "snap the whip" style interplanetary launch system. On the other hand a 36,000km cable made of exotic materials is already going to be incredibly expensive without making it twice as long, and there's *lots* of alternative interplanetary launch systems once you're in orbit. The cable might just end at a small moon (large captured asteroid) a bit above geostationary - makes for a much cheaper counterweight, and a well-shielded base of orbital operations.