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« Russia's Emphasis on Nano Weaponry | Main | Atomic Engineering at Room Temperature »

January 31, 2009

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Tom Craver

I've posted this over at LiftPort forums, haven't gotten any response yet. Frankly it sounds like an elevator killer.

Maybe one of the more knowledgeable readers here can see a flaw in what I wrote.

"Wikipedia rates the peak van Allen proton radiation flux at around 9e9 per sq-cm per second, at 500KeV - far more than is needed to break a carbon atom loose. Assume carbon atom spacing of about 5 per nm, or about 2.5e15 atoms/sq-cm of exposed nanotube molecular surface area.

So every second, about 1 per 280000 carbon atoms might be impacted, causing damage. Maybe the charged proton would sometimes pass through without transferring damaging energy - so call it 1 per 1 million atoms, each second. The ribbon will be thin enough that essentially all carbon nanotube surface can be treated as "exposed" to the radiation flux. (It doesn't matter that the ribbon is loosely woven, BTW.)

So in about 100,000 seconds, the ribbon would have about 10% damage sites - let's suppose that's "sufficient to ruin the tether". So a bit over a day to ruin a large segment of the tether."

(Wikipedia also shows a graph indicating 2e8/cm^2 per second for >100KeV as the flux for a large zone of 1MeV protons, which might allow up to ~45 days of nanotube ribbon survival. But again, the text mentioned 9.4e9 protons/cm^2 as peak flux exceeding 500KeV, and since the elevator fails (or at least becomes unsafe) as soon as any segment degrades substantially, I think it makes sense to use the highest value.)

x-ray fluorescence

A space elevator is a proposed structure designed to transport material from a celestial body's surface into space. Many variants have been proposed and all involve traveling along a fixed structure instead of using rocket powered space launch. The concept most often refers to a structure that reaches from the surface of the Earth to geostationary orbit (GSO) and a counter-mass beyond...

bala

how much long cable u take?how many killometers to the sky?

Tom Huffman

Mike, Have you been following the news about the climber competition sponsored by NASA and The Spaceward Foundation? This will be a competition for a robot, powered by beamed energy, that can climb 1 km up a 1.5 km cable, supported by a helicopter, at 2 ms or better. The purse for this competition is currently $2 million; no one won the competition in 2006 or 2007, so the money has been accumulating.

There's an organization in the Kansas City area: The KC Space Pirates that is building a robot climber for the race, using volunteer labor and donations from individuals and corporations. I was at a presentation this weekend by Frank Smith of the KC Space Pirates, where he discussed the space elevator concept and their entry in the race.

Their robot uses motors, receivers, and logic circuits from RC racecars. Everything's off the shelf.

Their 2006 / 2007 models used light reflected up from mirrors to a solar cell concentrating array; those mirrors were standard full-length door mirrors, bought in bulk at Lowe's. This year, they've got a donated laser to beam power to the PV cells on their climber.

Frank had some interesting info from The Liftport Group: Liftport apparently has attracted the attention of British Petroleum (BP). BP is interested in putting up a solar power satellite, once the space elevators are in place and costs to orbit have come down. I think it's about time to get some interest in SPS going again in the USA. This was an American idea; I'd hate to see us lose our leadership to the Brits.

I asked Frank about the issue of radiation damage from the Van Allen Belts. Frank admitted Van Allen radiation would affect carbon nanotubes - maybe not as much as Tom Craver fears. Frank advises Liftport would send up regular repair climbers to add new material to the ribbon.

The possibility of finally opening up the space frontier (a dream that has been deferred for decades!) is exciting. What I regard as just as exciting is the fact that this is being accomplished by an open-source volunteer project. I know the giant corporations will try to capture the project, once the creative work has been done; but, maybe this can be an alternative business model for the future.

Tom Craver

Thanks for finding someone to follow up on the radiation angle, Tom H. I hope it isn't a killer issue.

It is something I think can be fairly easily determined, to a first approximation at least, via lab tests. A reasonable project for someone looking for a PhD, perhaps?

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