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Comment by ram1024 | Hacker News Reader

space elevators are at least 50 years away...

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

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.

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.

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