Space Elevator Challenge, which has for three successive years failed to live up to the vision of Arthur C. Clarke. Japan isn't waiting for a fourth, announcing plans to spend $7.3 billion on its own lift to whisk passengers (and cargo) 22,000 miles aloft on composite cables. It's the cables that are the problem, as they need to be 180 times stronger than steel and obviously much, much lighter. The Japanese are focusing on carbon nanotubes, and while they will need to be engineered four times stronger than current stock before they're up to the task, their highly conductive nature means they can not only support the lift vehicle but also power it. Useful, that, because the ride up could take a couple of days or even weeks, and astronauts will need some way to recharge their PMPs.