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: 2) by Immerman on Tuesday September 04 2018, @03:27PM (7 children)
As I recall the top end of a beanstalk-style space elevator needs to be in geostationary (equatorial) orbit, but it is possible for the bottom end to be a considerable distance from the equator. I forget how much though, and 36* is probably pushing it.
On the other hand - you don't really need to have anything under the beanstalk. The whole thing is supported from orbit, so the bottom end could be tethered to a floating barge just fine. Except for the weather - the open ocean is known for its sometimes extreme weather, and you probably don't want to have to deal with that. An extremely tall mountain peak, close to the equator, but well inland would be ideal, but those are in extremely short supply.
At any rate, seeing how badly positioned Japan is for a beanstalk, combined with the fact that even the strongest multi-walled carbon nanotubes made by man are about 7x too weak to include adequate safety margins for such a thing, it seems like a safe bet that they're NOT talking about beanstalks. Especially since there's no safe place for the "blast path" of something long enough to wrap around the Earth one and a half times if it breaks. (Minimum length of a beanstalk is 36,000km - and that requires a massive counterweight just beyond geostationary orbit)
Unfortunately, I can't read Japanese to tell if the "connecting Earth to a space station" bit was actually included in the press release, or an editor's comment. It's possible that this is just more Japanese posturing - they do a lot of talk and "preliminary experiments" around far-future space technology, but there are also far more technologies that still fall under the umbrella of "space elevator" but never get anywhere close to the planet's surface (and are far more realistic with existing technologies) . The fact that they're talking about moving cars along the cable suggests that they're not talking about a tumbling-cable skyhook, though they could still be talking about a bi-level space station - connect two space stations with a long tether and put them in orbit one above the other - the top one will be orbiting too fast for it's altitude, and the bottom one too slow, providing both with pseudo-gravity and allowing you to dock with the lower one at (potentially far) below orbital speed for low orbit and then ride an elevator to the higher one.
(Score: 0) by Anonymous Coward on Tuesday September 04 2018, @03:48PM (2 children)
"close to the equator, but well inland would be ideal, but those are in extremely short supply."
Yep. You can take a few minutes with Google maps, and the answer is obvious. And it isn't really just about a space elevator. The same attributes improve rocket performance as well.
(Score: 2) by Immerman on Tuesday September 04 2018, @05:48PM (1 child)
Quite. But a rocket doesn't *really* care much unless your payload is pushing it's operational limits. Even the equator is moving at only 460m/s, while at 40*latitude it's moving at 356m/s. Meanwhile LEO speed is over 7,000m/s - a 100m/s boost is handy, but it's still just a difference of 1.4%. Saves some fuel, but fuel is the cheapest part of a typical launch, and it's a rare payload that pushes the limits of its launch vehicle.
(Score: 0) by Anonymous Coward on Tuesday September 04 2018, @08:10PM
"it's a rare payload that pushes the limits of its launch vehicle."
Building such a thing will require many flights with many international payloads. The infrastructure costs alone are enormous, and uneccessarily redundant. There really needs to be a space port in a free trade zone, with a WTO/UN sanctioned policy that it may be used for non-military flights, by any country. There are only a few places in the world that have natural economic advantages for this sort of thing. If any of them built such an FTZ, they could probably bring millions of dollars in trade to their shores. Because even if, we are just talking a 1% payload availability increase, that still represents millions if not billions of dollars over the lifecycle of something like the ISS, space elevator or skyhook.
(Score: 2) by c0lo on Tuesday September 04 2018, @06:06PM (3 children)
It'd be the hell of a barge considering the "stalk" thickness. Feeling of guts, I don't expect anything thinner than 200m.
Add to this the power stations for the elevators crawling along the cable. Add to this the "docking/warehousing" space required to store the goods that need to be loaded or have just been unloaded.
Nope, my bet is a beanstalk will have the connection point on the solid ground.
(Score: 3, Informative) by Immerman on Tuesday September 04 2018, @06:36PM (2 children)
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.
(Score: 2) by c0lo on Tuesday September 04 2018, @07:40PM (1 child)
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.
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
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.