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Japan starts space elevator experiments

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Re: Japan starts space elevator experiments

#281

Post by rbanffy »

yogthos wrote: post #276
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…

A space elevator seems like a much better concept for the Moon. If we could make a permanent Moon base with a space elevator, then it would be possible to use materials from the Moon to assemble things in orbit. Such a base would make it possible to start exploring the rest of the Solar system in earnest.

Launching from the Moon is cheap - magnetic rail and solar power can do the job and cut the need for propellant significantly and there is water enough to make e lot of propellant for delta-v's you'll need. With all that slack, we can relax a bit with mass and use simpler techniques to build ships. A lot of 3D printing and automated manufacturing.

On the not-so-bright side, we'll have to develop new metallurgy and other industrial processes based on local chemistry.

Where would the counterweight have to be for one end to be in high Earth atmosphere, balancing atmospheric drag with lift and gravity? My math tells me the end would be traveling at a relatively tame 260 kph.

Re: Japan starts space elevator experiments

#282

Post by timonoko »

chris_st wrote: post #270
timonoko wrote: post #237

The Giant Space Wheel (of Seveneves) is so much more attractive than space elevator. That is a large mass on geostationary orbit having smaller pods rotating at the end of ropes. Those pods can be lowered to atmosphere and synchronized with earth rotation. Elevator pod comes down and can stay down maybe couple of hours and then jerked back to heavens. All energy comes from the sun - collected at the center station. S…

Does it need similar cable strength as the space elevator (as mentioned elsewhere in this discussion), or are its requirements easier to hit?

The mass of the pod is much less than the end-station of the space elevator. So the cable can be very thin at the far end. If the cable is tapering smoothly it weights 1/4, but it need not to do that, I think it tapers in some kind of exponential curve. So 1/16 might be quite reasonable assumption, but one needs recent college education to calculate that. On the other hand there are strong centrifugal forces, as the pod speeds up from standstill, which is also vividly described in Seveneves book.

Re: Japan starts space elevator experiments

#283

Post by schiffern »

leereeves wrote: post #256
jimmcslim wrote: post #252

Earlier quoted context omitted.

Wouldn’t payloads travelling up the space elevator and departing for the rest of the solar system and beyond ultimately deprive the earth of angular momentum and send it hurtling towards the Sun?

Not hurtling toward the sun, but payloads traveling up the space elevator would slow the Earth's rotation (the 24 hour daily rotation about the Earth's axis) in the same way an ice skater spins slower when they spread their arms. When the payload detaches from the elevator, the angular momentum of the Earth about the sun does decrease (some of the AM goes with the payload) but the mass of the Earth also decreases, an…

>the angular velocity of the Earth about the Sun doesn't change.

It does if your spaceship escapes from Earth in a prograde[1] direction (equivalent to Earth throwing a ball forward, causing a retrograde reaction upon the Earth). This type of escape trajectory is necessary to reach any destination farther from the Sun (Mars, asteroids, etc). It's a tiny change obviously, but it's non-zero.

Note that returning from Mars/asteroids and aerobraking should add angular momentum, speeding up the Earth and at least partly counteracting this effect.

[1] https://en.wikipedia.org/wiki/Retrograde_and_prograde_motion

Re: Japan starts space elevator experiments

#284

Post by theothermkn »

Aeolun wrote: post #207
Bahamut wrote: post #127

Earlier quoted context omitted.

The satellite issue is why I don't think a space elevator as currently conceived will ever make it.

If you have a cable capable of holding a space station and counterweight, no satellite is going to stop it.

> If you have a cable capable of holding a space station and counterweight, no satellite is going to stop it.

A satellite impacting the tether will definitely "stop" it, in that it will, at the very least, melt an impact crater into it if the cable is wide enough to not be cut. It is unlikely that the cable will be that wide. I feel like a broken record, lately, but the dominant concerns of impact modeling at orbital velocities are (a) mass and (b) energy. Everything traveling at 8 km/s effectively splashes into whatever solid object it hits, both because the room temperature shear resistance of the materials involved is orders of magnitude less than the shears involved, and also because the kinetic energy is dumped into thermal energy, melting or vaporizing the materials involved. One tends to get results like: (https://www.esa.int/spaceinimages/Images/2009/02/Hyperveloci...) That link notes that pressures of 365 GPa are reached, and typical yield stresses of theoretical nanotube cables are around 100 GPa.

A carbon nanotube cable is unlikely to be more than an inch or two across at LEO. You need that kind of strength to beat the space-elevator-equivalent of the rocket equation, which governs the taper needed to get the cable to even support its own mass in Earth's gravitational field.

Re: Japan starts space elevator experiments

#285

Post by baby »

baby wrote: post #269
samstave wrote: post #219

Earlier quoted context omitted.

The fact that we are talking about a japanese company called Obayashi making a carbon nanotube elevator to space is very cyberpunk to me. Reminds me of Ono Sendai making wetwire jacks to the internet.

Makes me think of Gunmm/battle angel alita

here how it looks: https://www.google.co.uk/search?biw=1280&bih=629&tbm=isch&sa...

Re: Japan starts space elevator experiments

#286

Post by kurthr »

yogthos wrote: post #276
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…

A space elevator seems like a much better concept for the Moon. If we could make a permanent Moon base with a space elevator, then it would be possible to use materials from the Moon to assemble things in orbit. Such a base would make it possible to start exploring the rest of the Solar system in earnest.

Putting an elevator (or more likely a sky hook) at a lunar Langrange point makes some sense, because the tether doesn't have to reach the entire distance if we allow for 0.2km/sec injection/drop-off speeds. That's important, because lunar elevator/hooks are much longer than earth based equivalents, even though their strength and taper ratios are much more achievable (e.g. polyethylene 4:1). You'd want to keep launched weight for the tether as low as possible.

A huge advantage is that a hook at the far lunar Lagrange 2 would be very close to escape velocity (e.g. asteroids or GEO).

http://hopsblog-hop.blogspot.com/2016/08/lunar-sky-hook.html

http://hopsblog-hop.blogspot.com/2015/05/eml2.html

Re: Japan starts space elevator experiments

#287

Post by marcosdumay »

enraged_camel wrote: post #217
thoughtstheseus wrote: post #185

Earlier quoted context omitted.

Material science is tough. Check out engine/turbine material science developments. It can take >decade to get new materials into planes.

Yeah but isn’t that because aviation is an extremely highly regulated industry?

As a rule, the aviation industry auto-regulates first, and government regulators come later. That's the patter on most of the changes.

So, not really. It's a highly regulated industry, but this is not the bottleneck.

Re: Japan starts space elevator experiments

#288

Post by jessaustin »

BurningFrog wrote: post #216
jessaustin wrote: post #194

Earlier quoted context omitted.

They'll be roomy just as soon as it isn't exorbitantly expensive to transport material to space. So, possibly sometime after this elevator is operational...

The slightly counter intuitive point is that you only have to transport wall material. An inflatable "house" is conceptually completely possible. Airplanes have to be small because of air resistance. Space stations have no such constraints.

Inflatable, sure, but not a balloon. Micrometeors/space junk are a threat, and more so for bigger inflated objects.

Re: Japan starts space elevator experiments

#289

Post by marcosdumay »

timonoko wrote: post #282
chris_st wrote: post #270

Earlier quoted context omitted.

Does it need similar cable strength as the space elevator (as mentioned elsewhere in this discussion), or are its requirements easier to hit?

The mass of the pod is much less than the end-station of the space elevator. So the cable can be very thin at the far end. If the cable is tapering smoothly it weights 1/4, but it need not to do that, I think it tapers in some kind of exponential curve. So 1/16 might be quite reasonable assumption, but one needs recent college education to calculate that. On the other hand there are strong centrifugal forces, as the…

There is an exponential relation between the length of the cable and how strong a material you need for it.

It comes from the cable needing to support itself, not unlike the rocket equation that comes from the rocket having to propel its own fuel.

Re: Japan starts space elevator experiments

#290

Post by akho »

wallace_f wrote: post #258
Latteland wrote: post #180

Earlier quoted context omitted.

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... .

Of course whenever we see a little bit of a pattern, we use a little bit of our ability with this language called math, and declare a law. Calling it a short-term pattern that may or may not continue into the future wouldn't help us feel smarter than the other people in the room.

Yet it somehow helped you.
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