Thursday, May 25, 2006

Response to "Space Elevator is Doomed" meme

Tom Nugent published a reply to the this letter in Nature by N. Pugno and the spate of the space elevator won't work and I told you so meme.

There’s been some discussion recently (as well as emails sent directly to us) about the Nature letter which summarizes an article by N. Pugno predicting that the maximum strength possible in bulk CNTs will be roughly 30 GPa (as opposed to the 130 GPa predicted by Edwards 4+ years ago).

I posted about the paper mentioned in Nature to our forums back in January, and some (mostly non-LiftPort) people responded: Here is what I just wrote in an email about the issue:

I’ve discussed the article with a couple of CNT researchers, and they say that they’re not convinced by the paper. My attitude is that we have to wait and see what really happens, because there’s a lot about carbon nanotubes that we don’t know yet.

Despite anyone’s predictions, we won’t know what the material will be like until it’s made. There’s a LOT of other work that needs to be done on SE development regardless of what the material winds up being. And in the “worst” case, you can still build a space elevator on the moon with near-term materials.

One thing to remember is that, even if bulk CNT were limited to 30 GPa, we could still build the space elevator. It would just become limited by finances. That’s because, with a density of 1300kg/m^3 and a strength of 30GPa, the mass of a seed ribbon (using the same assumptions as in my November article - safety factor of 2, and 1,000kg capacity) would be roughly 3,440 tonnes (i.e., 3.44*10^6 kg), or roughly 170 rocket launches (using current medium-lift rockets) to loft it (i.e., ~80 times as massive as in the 2002 NIAC report). The expense and logistics of creating a seed ribbon at that point (assuming you’re launching from Earth) becomes much more daunting, but not impossible.

A week ago we were saying what we've been saying all along - we don't know what we don't know, we're exploring the options, to reach a go no-go point in 2009ish. It is worthwhile to explore the options in light of the potential benefits.

We're still saying that but in light of the 'neener neener we told ya' blog posts we might look like happy optimists instead of dour pessimists. Amazing how you can maintain the same position but appear to have shifted sails.
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