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Space Elevator May Become Reality
mojotek writes: "The NASA Institute for Advanced Concepts has a study(15Mb pdf) about the feasibility of a "Space Elevator" comprised of a 22,000 mile long cable built out of carbon nanotubes. In theory, it would be able to carry loads of 20 tons to space without using a single rocket engine. Sounded way too sci-fi for my taste at first, but this article at TechTV actually helped fill in the holes."
To transport you (70 kg) up to an altitude of 200 km would take roughly 140,000 kilojoules of energy (you do the math ... first year physics stuff). However, they can't just lift you, they also have to lift a vehicle containing you. Say the vehicle weighs 500 kg for every person it can carry -- this would take rougly 1,000,000 kilojoules. If they do this electrically (which is one of the more expensive forms of energy), at 100% efficiency it would eat up roughly 300 kWh of energy. At 0.30/kWh (say), that's roughly $100.
Of course, a clever engineer would realize that every vehicle going up eventually goes down ... so the vehicle on the way down could be used as a generator, feeding power to the load of a vehicle going up. Equally obviously, we're not considering the amortization of the construction cost, which would be monumental.
Toronto-area transit rider? Rate your ride.
Robert Heinlein (iirc) once commented that low earth orbit (LEO) is halfway to anywhere, and that's even more true of geosynchronous orbit (GEO). It takes a *lot* of fuel to get out of the earth's gravity well, and getting to GEO for the cost of electricity (provided by in-space solar cells!) would profoundly change everything.
If you want to leave earth orbit, you take a second elevator that runs from geostationary station out to the anchor and let go. Depending on the length of this section, you'll have a ballistic launch to anywhere else in the solar system. Well, you'll need a modest amount of fuel unless the plane of earth's orbit is exactly aligned with your destination, but you'll need orders of magnitude less fuel than you need today, and you can get that fuel up to the launch point for the cost of electricity alone.
If you want to leave the solar system, you let go of the upper elevator and hop to the center of a freespinning tether, then inch outward. When you reach the end of this tether, you could be traveling at a few percent of c. You'll be at Alpha Centari within 100 years... and a second tether there could capture you and slow you down. That's too long for passenger traffic, but brief enough that interstellar colonization is a realistic possibility by the end of the millennium.
So all things considered, I think research into carbon nanotube space elevators has better long term potential than anything rocket propulsion technology. Even antimatter propulsion, excluding some unknown mechanism to mass-produce anti-atoms.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken
I was just out of college (iirc) when the first popular discussion of beanstalks came out (Charles Sheffield, in some long-dead Baen book-zine).
The numbers were so ludicrious that he repeatedly apologized for wasting our time. Of course this was a flight of fancy, the numbers were orders of magnitude larger than the strongest known materials. Yet, if "ultronium" could be developed from some exotic material....
Then buckyballs were discovered. Then buckytubes.
The fact that this is even "just" possible with known materials less than 20 years later is mindblowing. I can only compare it to the confident RSA predictions in Scientific American (which I also remember when it first appeared) that RSA-128 would take millions of years to crack. We all know how well that prediction held up.
Given this perspective, I don't think it's unreasonable for NASA to spend some serious money considering its options if/when stronger materials become available. It's easier to believe that even stronger materials will be discovered (e.g., perhaps by putting foreign elements within the tubes to manipulate quantum properties) than that we've suddenly hit the ultimate barrier.
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken