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Japan starts space elevator experiments
Article: https://www.electronicsweekly.com/news/business/japan-starts-space-elevator-experiments-2018-08/
HN thread: https://news.ycombinator.com/item?id=17898152
I know some people here have strong opinions about space travel, which came up during the Elon Musk topics on Tildes. I wonder if, based on the limited information we have, people think Japan is taking the right approach with the space elevator; whether the cost estimate ($9 billion) sounds reasonable; and if you think they can succeed?
Always on board with the development of non-rocket space launch options. I feel like it's a bit of a blind spot in the current New Space culture. Bezos and Musk are focusing on bigger and bigger reusable rockets, which is fairly straightforward from an engineering perspective and a decent enough way to marginally reduce launch costs, but both of them could afford to be looking into more exotic solutions.
That said, I feel like space elevators are only a popular idea because most people don't know about better options. A space elevator can only be built out in geostationary orbit, can only be connected to equatorial sites, and transit to orbit takes nearly a week, through the Van Allen belts. And unless there've been major breakthroughs of which I was unaware, we still can't actually make the cable, so it's a moot point. I'm not even sure this experiment is strictly about space elevators, since cable cars moving along a zero g tether is not really useful experience, the space elevator is going to be under gravity for basically the entire trip, and the dynamics of tethers in geostationary orbit, where it does become 0g, are somewhat different.
One of said better options would be an orbital ring. It's basically a big steel cable put into orbit, strung out across the circumference of the planet. It gets spun up to above orbital speeds to create supporting centrifugal force, then cables held stationary with respect to the ground using magnetic bearings are lowered to Earth.
Here's the list of advantages over a space elevator, since it's too long to elegantly be put into a sentence:
No new materials needed. We could build one tomorrow.
A ring can service any point at any latitude.
The trip to orbit takes about an hour tops, depending on the acceleration you want.
The ring can pull double duty as inter-city high speed rail, except at speeds that eat the hyperloop for breakfast. The real limitation is transfers, as a single ring only covers stuff under a particular orbit. Conceivably you could commute from NYC to Sydney in under an hour, for the cost of electricity.
It makes space based solar power realistic beyond just reducing launch costs, since rather than having to set up large rectennae for beamed power, you could just send electricity down the cable.
You could set up hanging space stations on the ring that experienced full gravity. Still need to run life support, but thanks to transit speeds, that's free real-estate a maximum of about an hour from any ring-serviced point on Earth. And ten or fifteen minutes to a particular point if it's right next to a cable.
Since they're actively supported, they can be built at any altitude, so long as the central rotating cable is spun up to sufficient speeds. If you encased it in vacuum, you could build an orbital ring as low as it could get without running into stuff.
I could go on. I've heard some more exotic proposals that you could take small asteroids and lower them to the ground, not just mining them for resources, but using regenerative braking to harvest their kinetic energy. But at any rate, this is the system I think we should be investing in. I do feel like 9 billion is a decent estimate for the cost of a space elevator, if you discount the years of research before we'll be able to build one. But for around 100 billion, we could build the first orbital ring. And with the reduction in launch costs that brings (cheaper than a space elevator actually, $0.05/kg to orbit), the subsequent ones are effectively free.
Thanks for bringing up orbital rings!
Here is a great Isaac Arthur video on the topic.
As always, this video is a bit futurology too, but he does cover some basics pretty well.
How the hell have I never seen this channel before. Oh, that's some tasty brain candy.
You've just fallen down the rabbit hole. I'll see you in two weeks.
Hey welcome to Arthursday! (That’s the day he usually releases a new video.)
Another, much newer YT channel, which you may find interesting is ParallaxNick. That channel is more focused on astronomy and astronomy history. He’s been blowing up a bit recently, and for very good reason.
Yup, I've seen it. Big fan of his channel, glad he's getting these ideas out there.
That is so fucking cool... I doubt we'd see anything like this in our lifetimes, but still so cool.
What happens when an orbital ring breaks? My physics is incredibly rusty, but in the absence of air friction, wouldn't vibrations get magnified along the length of the cable? And since it's rotating with the earth, there would always be a large amount of kinetic energy waiting to go haywire. It's scary to think of an earth-sized whiplash.
(I just realized your username is "space travel"; when I saw it before I always read it as "specter-ville")
Yeah most people do, hah.
On a cable breaking, answer is that it depends. If we're talking on a fully developed ring, where the cable is shrouded throughout its length with a casing supported by magnetic bearings (which it probably would be early to protect against debris impacts) I don't think it would be too bad, since the centrifugal force would just be absorbed by the bearings, which is what the whole thing is supported by anyway. Strictly speaking, if you've got magnetic containment along the whole thing, you don't even need a discrete cable, you can just use a high speed stream of iron particles. So I don't think the cable snapping would do too much.
But if that happens without containment, the results depend on how much higher than orbital velocity the cable was at. If it's during construction, nothing happens. The cable's rotation is just its orbit, so its position is stable. If it is going faster though, yeah I think the whiplash is what happens.
But this is actually another advantage over space elevators. Because the ring's going faster than orbital speed, the whiplash goes out, into a higher orbit. Anyone on the ring is probably dead or heavily injured from the acceleration, but that's probably not many people because such a break would have to happen early in the ring's construction.
Space elevator breaks, however, are far more likely and far more deadly. A space elevator "cable" is really more like a ribbon, with a fairly large surface area. And that ribbon crosses through every orbit under it. Meaning that unless the space elevator cable is actively being maneuvered, every one of the over 4,000 satellites currently in orbit will eventually crash into it. Plus every piece of space junk. If that maneuvering stops for any reason, you risk a cable break. Orbital rings, due to being actively supported, can simply be built lower than any operating satellites. Though you would have to track re-entries.
And since the space elevator cable is operating under gravity, all of the thousands of tons of cable crash right down to Earth at high speed. I'm not sure if the cable also wraps around earth doing massive damage to everything in its path, but depending on where the break is and how much velocity is imparted to the broken strand of cable, I think that's a distinct possibility. Only in this scenario, the end of the whip is on the ground.
How would you get that into space and up to speed?
The ring's got short (~300-500km) cables made of conventional materials that go to the ground, which can connect to anything within around 100km of its orbital path. You ride up to space on a cable car, then accelerate along a track parallel to and supported by the ring until you're at orbital speed. Or higher, these things can actually launch things directly on to interplanetary trajectories.
EDIT: Reading comprehension fail. You could launch it all up from the ground for a few hundred billion at current prices, less than a hundred billion with new systems under development like BFR. Expensive, but even at current prices, cheaper than many infrastructure projects it could supplement, like the Interstate Highway System.
The biggest issue is getting all that > 40,000 km of mass up into LEO, right? Building it from asteroid mining might make the most sense?
You mean the mass of a 40,000km cable? The relevant number there is 180,000 metric tons. Asteroid mining would be the way to get it built with the fewest launches, but launch costs have fallen enough that we could just build a ring by sending everything up from the ground. Just by chartering Falcon 9 launches at current prices, assuming no bulk discount, we could get one built at a bargain cost of roughly 0.08 Iraq Wars, or somewhat less than the Interstate Highway System. If BFR pans out, NASA could build one if they dedicated their current budget to it for 5 years, with a fairly conservative launch cost estimate of $500/kg.
Holy crap, I had no idea the mass required was that low. Why aren’t Musk and Bezos talking about this?
I know, right? And that's just the number for Birch's orbital ring proposed for launch aboard the shuttle back in the 80's. You can build them smaller if you want to, but at the cost of lifting capacity.
Although there are the considerations that this is something completely new in spaceflight, whereas Bezos and Musk are just iterating on ideas we've had since the 50's, I think the real reason it doesn't get talked about much is because it's a fairly obscure idea that doesn't yet have a lot of mind share, compared to the space elevator. Oddly, I did see a post about them on one of the SpaceX subs a while back, and it was heavily downvoted. Few decent threads in the comments but a number of users were castigating the OP for daring to suggest that dear leader Elon's reusable rockets weren't the beyond-criticism pinnacle of spaceflight. I guess building a ring around earth does sound crazy, but the amount of cable used is actually less than the space elevator and it doesn't need an anchor.
I swear I'm just tripping over other forgotten advantages in these followup comments.
Does anyone here have a heavy twitter account? We need to troll those two guys with things like:
Do we even know of any materials capable of withstanding the forces required for a space elevator cable? I thought the carbon nano-tubes we can currently manufacture are pretty small and nowhere close to being sufficient in strength. And if that's the case, I am honestly wondering where they got the $9B estimate from.