In the 1980s, Jim Hollopeter helped design rockets that shot into orbit. Today, some of those launchers are still cluttering up space, and he wants to wash them away with a rocket-powered water gun.

Like many aerospace engineers, Mr. Hollopeter is worried about thousands of pieces of useless equipment circling Earth.

Bits of spent rocket boosters, old exploded satellites and tools dropped by space-walking astronauts are just some of the trash racing along in the near-vacuum of space.

The volume of man-made space debris has grown so large that scientists say garbage now poses a bigger safety threat to the U.S. space shuttle than an accident on liftoff or landing. The International Space Station occasionally fires thrusters to dodge junk.

The problem hit home Feb. 10, when a defunct Russian military satellite smashed into an American one used for commercial communications, spewing shards across thousands of cubic miles.

The crash prompted Mr. Hollopeter to refine designs for a concept he had long toyed with: Using aging rockets loaded with water to spray orbiting junk.

His idea is that the extraterrestrial shower would gradually knock refuse down toward the atmosphere, where it would burn up, as would the launcher. The water would turn to steam.

"We need to treat space like a national park — carry out what you carry in," says Heiner Klinkrad, who runs the European Space Agency's Space Debris Office in Darmstadt, Germany, and is chairman of the global Inter-Agency Space Debris Coordination Committee.

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