Japan starts space elevator experiments • Hacker News Board

Re: Japan starts space elevator experiments

#221

Post by mirimir » Mon, Sep 03, 2018, 5:04 AM UTC

larkeith wrote: post #200

ridgeguy wrote: post #179

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 energ…

(In case you were unaware, this is the Coriolis force)

But this is the vertical component of the Coriolis force, which is usually negligible. Yes?

Re: Japan starts space elevator experiments

#222

Post by mirimir » Mon, Sep 03, 2018, 5:10 AM UTC

blahedo wrote: post #29

> "...six oval-shaped cars, each measuring 18m x 7.2m holding 30 people, ... eight days ...." Whooooa. Let's think about this for a second. Eight days means people need to sleep (and not just sitting up in a chair, no matter how comfy). At 1m x 2m per bed that would be a 15m x 4m space even without aisles to walk between the beds or down the middle or any sort of privacy separators. Also, a bathroom and actual washin…

Hey, Stephenson had people living long-term in spaces that size, in Seveneves. That didn't turn out so well, but eight days isn't that long.

Tube beds could be close packed, and people could sleep in shifts. Also, one can survive just fine with just a washcloth and towel, and a source of warm water.

Re: Japan starts space elevator experiments

#223

Post by adrianN » Mon, Sep 03, 2018, 5:12 AM UTC

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?

Those regulations are there for a reason. Safety is important. You don't want your space elevator climbers to fall down. A ripped cable would also be a pretty expensive accident.

Re: Japan starts space elevator experiments

#224

Post by adrianN » Mon, Sep 03, 2018, 5:18 AM UTC

Keyframe wrote: post #77

p1mrx wrote: post #54

Earlier quoted context omitted.

The medical technology for human stasis doesn't seem particularly unattainable, when compared against building a carbon nanotube tether into orbit. Some mammals are able to hibernate for months.

So far, for humans, that lives within same realm that warp drives occupy in science fiction.

No, we don't even know if warp drives are allowed by the laws of physics. We have a pretty good idea how to do hibernation: Saturate the tissue with some cryoprotectant and freeze it very quickly. The problem is that we don't have a cryoprotectant that is sufficiently non-toxic and we can't freeze anything as big as a human quickly enough.

Re: Japan starts space elevator experiments

#225

Post by tempestn » Mon, Sep 03, 2018, 5:31 AM UTC

metafunctor wrote: post #218

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…

Article says they are going to use a steel cable.

Where did you see that? I see this in the article: "Carbon nanotube is the most likely material to be used for the cables."

A steel cable would have far too low a strength to weight ratio to work in a space elevator.

Re: Japan starts space elevator experiments

#226

Post by pankajdoharey » Mon, Sep 03, 2018, 5:45 AM UTC

If they could do it would be so cool, and another one of Arthur Clarkes ideas turned to reality after Geo Stationary satellite.

Re: Japan starts space elevator experiments

#227

Post by peeters » Mon, Sep 03, 2018, 6:00 AM UTC

jessaustin wrote: post #193

bencompanion wrote: post #122

Earlier quoted context omitted.

The end of this cable would be 36000km up, compared to the ISS's 400km. The first space elevator would primarily be used to shift stuff, rather than people at first - there's no point having convenient transit for people if they've got nowhere to go at the other end.

That's where the end of the cable is, but there's no rule that that's where anyone has to get off the elevator.

Interesting thought. Note that getting off 300 km up would not put you in orbit; you would lack the orbital velocity required for that. So if you get off there you'd have to burn around 8 km/s of delta-v, which is quite a bit of fuel to haul up.

For efficiency you'd want to go higher. There'd be a point much higher than 300 km where detethering would put you into a highly elliptical orbit where the periapsis is 300 km. Then you'd just have to burn retrograde to circularize. Off hand I'm not sure what the math for that would be but it should be pretty simple algebra.

Re: Japan starts space elevator experiments

#228

Post by [deleted] » Mon, Sep 03, 2018, 6:09 AM UTC

ridgeguy wrote: post #179

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 energ…

[deleted]

Re: Japan starts space elevator experiments

#229

Post by rapnie » Mon, Sep 03, 2018, 6:11 AM UTC

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…

I agree on the publicity stunt feeling. Space elevators are thought-provoking stuff of science fiction. It would be fantastic if we could build them.

Most I've read on the subject (this article included) are very thin on details, or point out the great scientific hurdles and breakthroughs that still need to be overcome / made.

This article made me think of the publicity stunt some years ago to build a mountain of 3,560 feet high in The Netherlands for $432 billion. The stunt was taken seriously and became world news:

https://www.businessinsider.com/400-billion-manmade-mountain...

If this is indeed a PR stunt I wonder if it would reflect positively or negatively on Obayashi? Would be like proposing an unrealistic, probably under-priced project. Of course they don't say when it can be realized..

Re: Japan starts space elevator experiments

#230

Post by TeMPOraL » Mon, Sep 03, 2018, 6:16 AM UTC

mrep wrote: post #213

cuddlybacon wrote: post #108

Earlier quoted context omitted.

Kelly and Zach Weinersmith discuss space elevators in their book Soonish. The summary of the downsides is: * If would need to be the most precisely engineered thing we've every produced just to stand a chance of being good enough. * Because of that, it will be particularly sensitive to wear and tear. How the maintenance would work is an open question. * It will probably attract terrorists like crazy. * It needs to ne…

I love the idea of space elevators, but I agree that it probably won't be practical on earth for a long time if ever. > It needs to never get struck by lightning. It is a particularly attractive lightning rod. Haven't buildings solved this problem with lightning rods? On another note, I am personally fascinated by space elevators which is why I am somewhat interested in going back to the moon where we can build a spa…

Yeah, I've never seen a reasonable explanation for that either. If the car is a Faraday cage, and the cable is conductive and grounded, what's the problem?

The only thing I can think of is that all that energy unloaded into cable at once might ablate some of it, causing it to no longer be able to handle the tension.