There’s a new Kickstarter project, aimed at setting the stage for a lunar space elevator. Space-elevator backers are trying to restart a competition for ultra-strong tethers. And a Japanese company has pledged to get the thing built … by 2050.
The idea of building a "railway to the sky" has tantalized dreamers for decades: Just send a satellite up to geostationary orbit, 22,000 miles up (36,000 kilometers up). Send one line back down to Earth, and another line up to an altitude of about 100,000 miles (160,000 kilometers) with a counterweight at the end. Secure Earth's end of the line so it's rock-solid, then start sending robotic climbers up and down the line, carrying cargo and passengers.
The key sticking point has to do with the tethers, or cables, or ribbons that would be required to connect a terrestrial liftport with the elevator's orbital destination. Whatever they're made of, that connecting material would have to be stronger than any material that's manufactured today. A synthetic polymer called Zylon ranks among the strongest available, and space-elevator advocates measure its strength per unit of density at 3.9 megayuris. (The "yuri" is an unofficial measurement unit that was named after Russian space-elevator pioneer Yuri Artsutanov.) The specific strength of steel is about 0.5 megayuris. But the stuff of space elevators would have to be on the order of 30 to 100 megayuris strong.
For years, NASA offered $2 million in prizes to encourage the development of 5-megayuri material, but that challenge expired after last year's contest. The International Space Elevator Consortium is trying to revive the prize program at a lower level, but that won't happen in time for this year's conference.
Carbon nanotubes are a good candidate, but lots of technical obstacles will have to be overcome in order to produce long, wide ribbons of carbon nanotubes that are strong enough and resilient enough to do the job. David Horn, the chairman of this weekend's conference, says boron nitride nanotubes offer 75 percent of the theoretical strength of carbon nanotubes and may be easier to manufacture.
Whether they're made of carbon or boron nitride or polymer, stronger materials will produce a payoff long before the elevator gets built — in the form of lighter, more fuel-efficient automobiles, airplanes, boats and, yes, even spacecraft.