The most obvious sign that there is a lot of junk in space is how much of it has been falling out of the sky lately: a defunct NASA satellite last year, a failed Russian space probe this year.

While the odds are tiny that anyone here on Earth will get hit, the chances that all this orbiting litter will interfere with working satellites or the International Space Station, which dodges pieces of debris with increasing frequency, are getting higher, according to a recent report by the National Research Council. The nonprofit group, which dispenses advice on scientific matters, concluded that the problem of extraterrestrial clutter had reached a point where, if nothing was done, a cascade of collisions would eventually make low-Earth orbit unusable.

"NASA is taking it very seriously," Mason Peck, chief technologist for the National Aeronautics and Space Administration, said. "It is becoming an important issue."

There is a straightforward solution to the problem: Dispose of the space junk, especially the large pieces, before they collide and break into smaller ones. And so researchers are stepping in with a variety of creative solutions, including nets that would round up wayward items and drag them into the Earth's atmosphere, where they would harmlessly burn up, and balloons that would similarly direct the debris into the atmosphere. Also on the table: firing lasers from the ground. Not to blow things up, which would only make more of a mess, but to nudge them into safer orbits or into the atmosphere.

20,000 pieces in orbit

Just last week, researchers at a top Swiss university, the Federal Institute of Technology in Lausanne, announced that they were designing CleanSpace One, a sort of $11 million vacuum cleaner in the sky, that would be able to navigate close to a satellite and grab it with a big claw, whereupon both will make a fiery death dive.

The Swiss have only two satellites in orbit, each smaller than a breadbox, but they are concerned about what to do with them when they stop operating in a few years.

"We want to clean up after ourselves," said Anton Ivanov, a scientist at the institute's space center. "That's very Swiss, isn't it?"

The Air Force currently tracks 20,000 pieces of orbiting space junk, which includes old rocket parts and dead satellites.

For now, the risk is real but manageable. Satellite operators can dodge the big debris and armor their satellites to withstand impact with smaller pieces. But eventually, if not cleaned up, low-Earth orbit would become too perilous for people and satellites.

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NASA seeks orbital broom for space junk