The space elevator: going down?

Nature ^ | 05/22/06 | Jason Palmer

[KevinDavis]

Is it possible to make a cable for a space elevator out of carbon nanotubes? Not anytime soon, if ever, says Nicola Pugno of the Polytechnic of Turin, Italy. Pugno's calculations show that inevitable defects in the nanotubes mean that such a cable simply wouldn't be strong enough.

The idea of a space elevator was popularized in science fiction, where writers envisioned a 100,000-kilometre-long cable stretching straight up from the Earth's surface and fixed in a geosynchronous orbit. Payloads, or tourists, would simply ascend the cable into low-Earth orbit, eliminating the need for rocket launches.

[KevinDavis]

Why do I question this study???

[KevinDavis]

[SunkenCiv]

Arthur C. Clarke Stands By His Belief in Life on Mars
by Leonard David
7 June 2001

Clarke spoke last night, June 6, via phone from his home in Sri Lanka as key speaker in the Wernher von Braun Memorial Lecture series held here at the Smithsonian's National Air and Space Museum. Pouring over images on his home computer taken by the now-orbiting Mars Global Surveyor (MGS), Clarke said that there are signs of vegetation evident in the photos. Clarke repeated several times that he was serious about his observations, pointing out that he sees something akin to Banyan trees in some MGS photos.

[narby]

Why do I question this study???

I never did buy into the space elevator stuff. It's not possible to make a single molecule that long, so by necessity it will have to have a binder between them to transfer the load from one fiber to the other, as fiberglass resin does in Carbon Fiber composites. That's going to make the thing dramatically heavier.

And how did they ever think they'd handle the space junk issue? It's one thing to have the single point in space where a spacecraft is and be relatively sure that no other big point will hit it. But a line 10s of thousands of miles long going way past geosync, passing right through the Clarke belt with it's expended boosters and dead spacecraft would be hit constantly.

Without a plan to significantly clean up space below 30k miles or so, how could a space elevator ever be a serious idea.

[Yo-Yo]

Prior to nanotube technology, SF used "synthetic diamond" grown into a single long crystal chain to do the same thing. Carbon nanotubes and diamonds are closely related.

The thing I always questioned about the idea was how do you keep the two cars balanced. It isn't enough to dangle a cable from geosyncronous orbit, you also have to dangle one up the same distance, and you have to move two cars along the two cables to maintain balance in the system.

With the centripedal forces in play, even a small imbalance in the system would tear it apart. So then if you can only lift a payload from Earth by also pulling an equal mass from 2x geosyncronous orbit (how did it get there in the first place?), how do you send down the empty car for another load?

Also, no orbit is exactly circular, so the relationship between the geosyncronous orbit platform and the earth's surface would constantly be in flux by a minor amount. I work in television, and when you uplink video to a satellite then monitor the downlinked return video, you can watch the change in the timing between the two videos change as the distance from the earth station and the satellite changes.