Thursday, December 22, 2011

Cost of a Space Elevator: $350 Billion (?)

NIST carbon nanotubes for sale
How much will it cost to build a space elevator? Here's one estimate for the raw material alone: $350 billion.

At least, that's the current cost of the carbon nanotubes, if you want ones free of impurities. NIST has started selling single-walled carbon nanotubes, certified to be free of certain contaminants: $865 for 250 mg of the stuff.

That's 61 times the price of gold, per ounce.

As I wrote in my recent Physics World article, a carbon nanotube is the only existing material that is both strong enough and light enough to satisfy the demanding engineering requirements of a space elevator. (Basically, you need a material that can hold up about ten thousand kilometers of itself without breaking.) It remains to be discovered how to combine something that basically looks like a pile of soot into something durable like you'd need for a space elevator ribbon, but let's assume the SmartPeople (maybe these guys) work that out. What's the price of just the CNTs?

Well, the mass of the elevator will depend on its length (which, in turn, depends on how much of a counterweight you can manage to attach its space-end), and on its shape (which would be some kind of taper, widest at geosynchronous orbit). You can play with these (and here is a great spreadsheet by Maurice Franklin that lets you do just that), but the length is likely to be about 100,000 km, and the GEO-to-end taper ratio about 2-4, so the mass is going to be somewhere around 105 kg.

At the NIST list price that will run you about $350 billion, or 0.5% of world GDP. Pricey even for Google.

Of course, this is just NIST's introductory price for uncontaminated CNTs -- it will likely drop by the time the elevator ribbon construction facility gets going.

And NIST will surely give you a big discount if you show up with a checkbook and say you want to buy in bulk.


Unknown said...

One of the most important reasons why a SpaceShaft is a better option for economical access to space.

Eric L said...

Kind of amazing if the tallest structure ever to be built will be built out of just 100 tons of carbon; I bet lots of apartment buildings have more carbon in them than that.

That's equivalent to 1000 barrels of oil, which would cost $100,000. Add a few zeros if the way to get pure nanotubes involves creating lots more impure nanotubes and sorting them out. There's certainly plenty of room for the price to come down if we can figure out mass production.

Honestly, if we can figure out how to do it for $35 billion, we should do it; that's four years of NASA's budget and it would make their budget go so much further after that.