Race on to build world's first space elevator | Hacker News Reader

Race on to build world's first space elevator

news.com.au

25 pointsryanwaggoner28 comments

I've always wondered why, if you have a material sufficiently strong to build a space elevator, you don't just use it to wind composite fuel tanks for conventional rockets? At 150 times the tensile strength of steel, for example, you could make a pressure vessel that holds 150 times the pressure that you can with steel. Taking the densities as similar (sigma/rho is the relevant parameter) that should make pressure-fed rockets not just viable, but hugely preferable to turbo-pump-fed systems. It seems like you'd recoup your capital outlay much more quickly, even if you did (eventually) use more material to launch an equivalent mass of payloads.

For reference, in Engines of Creation (iirc), Drexler outlines a personal launch vehicle that weighed ~100 lbs and could lift a single occupant to leo with one stage. I suspect that the guys that finally do build a space elevator are really just going to end up with a nice place from which to watch personal spacecraft launches.

I'm very happy about the fact that this is inevitable. The first nation to build it will have an order of magnitude if not more of an advantage when it comes to space travel costs.

Not being stuck at the bottom of a deep well is going to be a game changer.

I'm still not convinced that it's possible to make the kind of super-long, defect-free nanotube cables that are going to be required. I'll be very happy if I'm proven wrong, but I certainly wouldn't say it was inevitable.

I say it is inevitable because the benefit is so ridiculously high that at some point the costs of building it will be quite low compared to the economic advantage of having it. A projected budget of a trillion is paltry when you consider how many hundreds of millions are poured into space agencies every year.

You should watch the new episode of Mythbusters called Motorcycle Flip, as the side myth in it is testing if someone can actually escape from jail like some newspapers state the 'facts' like using human hair, bedsheets and toilet paper. As all three get proved plausible, it shows what can be turned into a cable.

When someone can make a rope out of single ply perforated (the easy-rip kind) of toilet paper, I think someone will find a way to make a cable out of nanotubes.

From what I've read of nanotubes, you might not even need an adhesive to hold the cable together as they have high levels of van der Waals force. If you simply splice all the ends together it's possible you'd have the worlds strongest material held together by the universes everlasting and powerful adhesive.

If you're interested in some commercial companies currently working on this, check out the LiftPort Group. http://liftport.com

I wonder why Perth? 2000 miles south of Hawaii makes sense since it's near the equator to maximize centrifugal force and tangential velocity during launch, but why Perth?

It is more economically feasible to transport materials to Perth.

Is there anywhere to read about the physics of this for a mechanical dummy?

Specifically I'm wondering, wouldn't the counterweight be pulled toward earth every time we use the elevator? Would we have to continually boost it?

Does the counterweight have to be in a geosync orbit, or the center of mass? If the latter, what keeps the counter weight in geosync?

What are the failure modes of this technology? It appeals mosly to SF fans, and every SF fan who has read the Ringworld novels will think of cities crumbled to dust by flailing nanowires...

The upper half would fly off, and the lower part would burn up in the atmosphere. I think.

I don't think it would burn up because its relative motion to the atmosphere will be zero apart from a relatively small vertical acceleration due to gravity. It would most likely come straight down on top of its base.

One of Kim Stanley Robinson's Mars books deals with precisely this, though on Mars, not Earth... It's the second book I think.

Important take home point: Failure of a space elevator is just all-round nasty on a global scale... The speeds that the cable attains as it falls, and its likely weight supposedly make for a very big impact along a very long point of impact (or should that be line of impact?)

Proof of concept at VC pitch meeting: Willy Wonka movie.

I have one word. Why?

Well there's only one reason for a male to risk death, radiation damage, bone loss, etc & it's not the rocks.

One word can also answer that - ego.

before they make a space elevator, they need to build a proper space station. The current one is tiny. I want something the size of an oil tanker.

but it would be much cheaper to build a cruise liner of a space station if we had a space elevator

space elevators are at least 50 years away...

we haven't even been back to the moon yet. let's be realistic

Why?

we've just now started created nanotechnological materials. it will be a significant amount of time before we can actually engineer with structures this size. also keep in mind a chain is only as strong as its weakest link, that means this nanotube "ribbon" has to be pristine and perfect throughout its entire length.

understand that the tether is only part of the equation, you need to construct the huge ass counterweight in space as well, and that doesn't get up there by itself, and we don't have an elevator to GET it there until we make the first one.

that's a thousand small details that have yet to be even addressed let alone discussed as to their feasibility.

just don't get your hopes up about seeing this in the near-term...

I thought that was the whole schtick (didn't read article yet but been reading about it). With nano tech we now had materials that could theroeticaly do it.

a chain is only as strong as its weakest link, [which] means this nanotube "ribbon" has to be pristine and perfect throughout its entire length.

To be precise, it only has to be as strong as its engineering factor of safety along its entire length. Also, fundamental to the understanding of composites is the transmission of loads from the fiber to the matrix. This load is transferred via shear pressures along the length of the fiber at the interface with the matrix. The net result is that the load is transferred along a very large area and results in a low shear pressure in the matrix. Composite engineering is a tricky business, but even with current fiber materials, you can build a part that has ~7 times the strength/weight of metals, much lower modulus of elasticity, and a linear fatigue curve.

you need to construct the...counterweight in space as well...and we don't have an elevator to GET it there until we make the first one

Most current plans actually unwind the tether from the middle. Then, in much the same way as cables are strung across canyons starting with a bow and arrow and a string, this initial tether is just strong enough to haul up another larger line, and so on. A single launch using any of the heavy lift vehicles in service today would be sufficient to launch the starting material into a suitable orbit.

Space elevators are just one way of avoiding the near exponential nastiness of the rocket equation. We currently have the ability to construct compressive towers that extend beyond the atmosphere. Build several of these, and park an electromagnetic accelerator on top, and you have something that gives you the same economics as the space elevator for a comparable price. The big problem with this scheme: building it would be politically impossible.

are you talking about this? http://arxiv.org/ftp/physics/papers/0701/0701093.pdf

Not just that. There are more recent calculations involving modern carbon composites somewhere in Google Groups.

We can build towers that extend beyond the atmosphere? I'd like to hear about that.

Not that it matters. The top of the atmosphere is usually marked as 120 kilometers up. Let's say you can build a tower one hundred times that tall, around 10,000 kilometers high. You've only reduced the speed needed by your electromagnetic accelerator from 11 km/sec to 7 km/sec. That's still like 15,000 miles per hour.

I'm all for dreaming big, but the other ways of leaving the earth are better.

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