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Japan starts space elevator experiments

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Re: Japan starts space elevator experiments

#171

Post by sandworm101 »

onion2k wrote: post #71
sandworm101 wrote: post #2

Carbon nanotubes are cool, but i will believe space elevators possible once someone shows me a carbon nanotube rope i can climb with. I'd settle for a bike or motorcycle chain. A nanotube-based shoelace would be worth a noble prize or two.

On a practical note, if you drop something on your foot you need to be able to take your shoe off quickly - cutting the laces is often the best approach. Shoe laces as strong as steel would likely lead to you losing your foot. Same goes for titanium wedding rings...

If you can biuld large enough nanotubes that you can weave them into rope, you can engineer in any properties you want. Anything from graphite dust to diamond is an option.

Fyi, the military has a specific way to lace boots so the laces can most easily be cut to remove the boot.

Re: Japan starts space elevator experiments

#172

Post by db48x »

krallja wrote: post #49
curiousgal wrote: post #45

Earlier quoted context omitted.

How much space would they get on the ISS either ways? It'd be a good practice.

They’re not going to ISS, they’re going somewhere in geosynchronous orbit.

But it's still an apt comparison. People live for long periods on the ISS, and the amount of space isn't likely to get any bigger during their mission.

Re: Japan starts space elevator experiments

#173

Post by dmurray »

snowmaker wrote: post #160

It's unclear to me if this is real or the continuation of a publicity stunt from Obayashi (who has been getting press about their plans to build a space elevator for years). I'm as excited about the theoretical concept of a space elevator as anyone. But the problem remains that no one can produce a cable even close to strong enough. This article has a good description of the material science problem: http://www.space…

We're only 1 to 1.5 orders of magnitude away from having a material strong enough? Maybe I've been working with computers for too long, but that sounds excitingly achievable.

Re: Japan starts space elevator experiments

#174

Post by sandworm101 »

eponeponepon wrote: post #55
Torkel wrote: post #14

Earlier quoted context omitted.

Given strength and size and other properties that carbon nanotube ropes would need have... Wouldn't a carbon nanotube shoelace be like the worst idea ever? ...strong as a steel cable, but so thin as to be hard to see and handle. And brittle and not so good at bending. => First it slices up your hands when you tighten it and then it breaks when you tie it :)

I believe the expectation regarding carbon nanotubes in the sphere of space elevators is that they would be woven and layered into a sheet of human scale; these sheets would be used to construct a curved ribbon for the gondola to climb. You could apply the same principle and weave a bootlace from them, but the limits of current technology would render that an exceedingly expensive bootlace.

Given the amount needed for a space elevator, it better be cheap as shoelaces. At 10s of thousands of miles they should have more than enough on hand to disrupt the shoelace market.

Re: Japan starts space elevator experiments

#175

Post by titanomachy »

dmurray wrote: post #173
snowmaker wrote: post #160

It's unclear to me if this is real or the continuation of a publicity stunt from Obayashi (who has been getting press about their plans to build a space elevator for years). I'm as excited about the theoretical concept of a space elevator as anyone. But the problem remains that no one can produce a cable even close to strong enough. This article has a good description of the material science problem: http://www.space…

We're only 1 to 1.5 orders of magnitude away from having a material strong enough? Maybe I've been working with computers for too long, but that sounds excitingly achievable.

Yeah, just wait 6-7 years and Moore's law should take care of it.

Re: Japan starts space elevator experiments

#176

Post by dmurray »

zmix wrote: post #137

> using six oval-shaped cars, each measuring 18m x 7.2m holding 30 people Hmmm...is that 30 people/car or 30 people/6 cars? You will be enclosed with them on 18m x 7.2m, that's 120m², for 8 days! The former case would sound like torture, in the latter case it could be done comfortably, though, but it would still require some good nerves by the travellers...

120 m² is a substantial 3- or 4-bedroom house. People endure a lot worse for much lower payoffs than going to space.

In spacecraft, Soyuz is about 6 m³ for three astronauts for two days. Apollo was 6 m³ for three astronauts for two weeks. The Japanese proposal is spacious in comparison.

Re: Japan starts space elevator experiments

#177

Post by ridgeguy »

perl4ever wrote: post #75
a1369209993 wrote: post #65

Earlier quoted context omitted.

You'd need to accelerate at 68 G's[0] (foreward for the first four minutes, backward for the last four). Not neccesarily unsurvivable, but your passengers (and most cargo) are likely to be unpleasantly pastelike. We should probably treat it more like commercial air travel than compressive-structure elevator rides. 0: 200kph*8day/8min/2min => 67.981081 gravity

TIL forwards acceleration is called "eyeballs in" and backwards is called "eyeballs out". It looks like 6 Gs is about as much as is feasible for an extended period of time.

Brief search didn't get me anything about longest ride on a centrifuge, which I guess would be the only way to test G-tolerance over extended periods. Where 'extended periods' means > an hour.

Any pointers to 6 Gs as being tolerable, for how long? Tnx.

Re: Japan starts space elevator experiments

#178

Post by jjeaff »

a1369209993 wrote: post #65
tomovo wrote: post #56

Earlier quoted context omitted.

Stairway to Heaven is about 8 minutes long, so they better work hard on speeding the elevator up to match that.

You'd need to accelerate at 68 G's[0] (foreward for the first four minutes, backward for the last four). Not neccesarily unsurvivable, but your passengers (and most cargo) are likely to be unpleasantly pastelike. We should probably treat it more like commercial air travel than compressive-structure elevator rides. 0: 200kph*8day/8min/2min => 67.981081 gravity

I don't think 68 Gs is survivable at all. At least not for more than a fraction of a second. 46 Gs for a few seconds is the most a human has survived that we know of.

10 Gs for 1 minute is lethal.

Re: Japan starts space elevator experiments

#179

Post by ridgeguy »

I'm curious about space elevator phenomena related to lateral ∆V.

At Earth's equator (zero altitude - i.e., on the ground), an object moves spinward at about 0.46 km/sec. In geosynchronous orbit, an object has to move at about 3.07 km/sec.

A space elevator car ascending from stationary on the equator to a terminal at geo altitude would require a tangential (lateral) ∆V of 2.61 km/sec. This is in addition to the energy needed for ∆ altitude-related potential energy change. Am I thinking about this right?

The faster the ascent, the greater the lateral reaction force on the elevator because ∆V/time increases. Has anybody done that model? I didn't find anything in a brief search.

The lateral ∆V also suggests it could get windy on ascent because the atmosphere rotates with the earth on a macroscopic basis. Maybe later tonight, I'll calculate lateral wind velocity as F(altitude) and see if I can fold in pressure drop to get wind pressures as F(altitude).

I would love to see even a prototype attempt in my lifetime.

Re: Japan starts space elevator experiments

#180

Post by Latteland »

titanomachy wrote: post #175
dmurray wrote: post #173

Earlier quoted context omitted.

We're only 1 to 1.5 orders of magnitude away from having a material strong enough? Maybe I've been working with computers for too long, but that sounds excitingly achievable.

Yeah, just wait 6-7 years and Moore's law should take care of it.

Okay, that's a joke people. There's no moore's law for carbon nanotube extension (that I know of). There is an analog of electric battery price reduction over time, about 15-30% per year. Here's a graph of it - https://electrek.co/2017/01/30/electric-vehicle-battery-cost....
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