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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.
(Score: 5, Interesting) by Immerman on Tuesday September 04 2018, @02:37PM (8 children)
Indeed. Skyhooks are commonly considered a form of space elevator, just not quite as iconic as a geostationary beanstalk.
On the bright side, they're potentially considerably more efficient than a stationary beanstalk since they're largely passive structures with no friction or motorized components to waste energy. And if you can manage the millisecond coordination required to dock with the top end to de-orbit, they can offer 100% efficient asynchronous orbital momentum transfer from returning payloads to launching ones.
They also have the slight advantage of being possible to build, since as AC alluded, even carbon nanotubes aren't nearly strong enough to make a beanstalk. As I recall multiwalled carbon nanotubes, the strongest material we've developed, are just barely strong enough to support their own weight over the 36,000km to geostationary orbit, with something like a 20-40% safety margin. Unfortunately, safe engineering practices generally call for a 900% safety margin even for comparatively low-risk structures like bridges.
And even bridges fail occasionally. If a beanstalk breaks, it'll potentially wrap around the Earth one and a half times, unleashing massive devastation across the path of its fall. The top end at least might burn up in the atmosphere - then again, it might not: after all it'd be FAR wider than the base, to support the weight of all the cable beneath it. After falling 36,000 km it might well manage to get through the atmosphere before most of it has burnt away. Especially since carbon nanotubes are quite possibly the best thermal conductors known to man - that cable might barely burn until the whole length is approaching it's flash point - at which point flames might end up racing down the length of the preheated cable, rapidly creating the largest fires humanity has ever dealt with (though the portions in the ocean would offer both a firebreak and cooling to the remainder.)
(Score: 0) by Anonymous Coward on Tuesday September 04 2018, @04:05PM (1 child)
Why not make a "sky ferris wheel" then and dock whenever you like?
(Score: 4, Interesting) by Immerman on Tuesday September 04 2018, @05:10PM
1) it's *far* more expensive.
2) you still need the same millisecond coordination unless the entire wheel rim is completely uniform and passive so that you can dock literally anywhere ("claws" on your ship to grab onto the ring? Supermagnets capable of holding your ship against the potentially multi-G centripetal force?)
3) even if the wheel rim is uniform, you still haven't dramatically improved the timing window in the challenge of passing through exactly the right piece of space at exactly the right moment. The top of the ring is traveling far in excess of orbital velocity, it's not like you can just drift close to it and grab it when handy - you've got to coordinate the lowest, fastest point of your very elliptical incoming orbit to reach the upper-wheel elevation at exactly the same moment as the top of the wheel is passing through that point. Get there a few seconds too soon and the wheel won't be there yet - too late, and it will have already passed.
What a a "wheel" really gains you is a spatially continuous selection of rendezvous points, meaning you can launch from, and return to, anywhere on the skyhook's orbital path without having to wait until a tether is in the appropriate alignment for your desired region (very handy, and well worth having if you can afford it). The rendezvous timing still needs to be nearly perfect though, you just have a bit more leeway in the exact position. And at the speeds you're traveling for a reentry rendezvous, even a full burn of your rocket isn't going to allow for much in the way of last-minute corrections.
My own preference to widen the rendezvous window is to use "docking harpoons" to buy a bit more leeway - as you approach a skyhook docking site you fire a harpoon at a "docking target" which securely grabs the harpoon and drags you along at the end of the attached tether (obviously your ship needs to be designed to support its weight on the harpoon tether). That buys you at least a few dozen meters of allowable imperfection, maybe even a few hundred, which means your timing can be off by at least a sizeable fraction of a second, and potentially several seconds, depending on the precise orbital dynamics of the skyhook.
(Score: 2) by captain normal on Tuesday September 04 2018, @05:05PM (1 child)
Wonder where you got 36,000 km? You don't have to go that far to be in space. The ISS is only ~410 km up.
When life isn't going right, go left.
(Score: 3, Interesting) by Immerman on Tuesday September 04 2018, @05:25PM
That's the elevation of geostationary orbit - the only distance at which objects can orbit above a fixed point on the Earth's surface (necessary for a surface-to-orbit elevator). And all beanstalks have to connect to a counterweight beyond that point in order to hold them up (by necessity they're lowered from orbit, not supported from below). It's also the "balance point" height at which maximum beanstalk tension is reached.
Anything orbiting closer is moving faster than the Earth's surface, and thus can't be connected to the surface. Much faster by the time you get as close as the ISS, whose ground speed is over 27,000 km/hour.
There have been some experiments using tethers to lower things into the atmosphere from orbit, but as you can imagine dragging a cable through the atmosphere at Mach 22 introduces some serious drag and turbulence issues - assuming you can avoid having the tether disintegrate from re-entry-style heating.
(Score: 4, Interesting) by captain normal on Tuesday September 04 2018, @05:24PM (1 child)
Also, the circumference of the Earth is a bit over 40,000 km, so a 36,000 km cable would not wrap around Earth once.
And the Earth spins west to east so a cable falling from geosynchronous orbit would wrap to the west across central Africa before reaching the Atlantic Ocean then across Northern Brazil, and parts of Columbia and Ecuador With the top end landing among the Island of the South Pacific.
When life isn't going right, go left.
(Score: 2) by Immerman on Tuesday September 04 2018, @05:39PM
Right you are - I carelessly overlooked the fact that Google gave me the circumference in miles rather than km.
I'm less certain about the direction the cable would fall though, I'm thinking it would be to the east. Consider: the cable isn't stationary, it's not being dragged down by the spinning of the Earth, it's *also* spinning west-to-east, and doing so considerably faster than the Earth's surface. Just like the outside of a spinning record moves faster than the inside, so does the outside of the cable - at geostationary orbit it's traveling east at about 3000m/s, versus the 460m/s of the Earth's surface, and it will be picking up speed the whole way down. As it loses altitude (and the associated moment of inertia) it must gain angular speed to conserve its angular momentum.
(Score: 0) by Anonymous Coward on Tuesday September 04 2018, @08:06PM
Also wouldn't the cable impacting the ocean (assuming it doesn't completely burn up) cause a giant tsunami along the length of the cable?
This would make an epic disaster film!
(Score: 2) by Spamalope on Wednesday September 05 2018, @12:15AM
I seem to recall some design variants that proposed the lower portion not be rigid and allow arc in the tether so there is some slack to work with. I think the idea was shock absorption and to allow a refueling boom like ability to 'fly' the lower end slightly to make capture less fraught. I didn't find the discussion with a quick search though, dammit.
I want to live to see this stuff work, dammit!