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Last December NASA and the Department of Defense hosted an international conference on ways to clean up the mess. The world’s space agencies already track the larger bits of trash, allowing spacecraft, especially manned ones, to evade them. And in 2007 the UN recommended some sensible preventive measures, such as draining propellant from spent boosters to keep them from exploding, and not using old satellites for missile target practice—which, coincidentally, China had done earlier that year.

But those guidelines won’t prevent accidental collisions; not every spacecraft can dodge the superfast flak. “For the next 50 years,” says Johnson, “we’re looking at a collision between two large spacecraft every five years or so.” That probably won’t be enough yet to trigger the Kessler nightmare. On the other hand, a working cleanup scheme seems just as far off.

“It turns out,” says Johnson, “to be a very, very difficult thing to do.” At the conference researchers discussed several ways of dealing with space junk. A long, electrically conducting wire could be hung from a dead satellite or other large bits of junk, tethering the junk to Earth’s magnetic field and dragging it into the atmosphere, where it would burn up. Or a collector satellite, a sort of space garbage truck, could simply scoop junk up, haul it down near the atmosphere, and release it into a death spiral.

For the bits of trash only a few inches across, which are hard to dodge but still damaging, a powerful orbiting laser might work. So might a more passive approach—a giant ball of foam that would sit in space like a spiderweb, sweeping up debris. The foam wouldn’t actually capture the debris; like the tether it would simply drain enough energy from the speeding bullets that they’d spiral into the atmosphere. “Of course,” Johnson admits, “launching a mile-wide Nerf ball might be difficult.” —Michael D. Lemonick

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