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By Denise Chow

It’s a hit! A harpoon designed to help clean up the hundreds of thousands of pieces of space junk now orbiting Earth passed a key test earlier this month when it successfully speared a piece of simulated debris.

As dramatic footage of the Feb. 8 test shows, a European satellite known as “RemoveDebris” test-fired a barbed titanium spear about the size of a writing pen at an aluminum panel attached to the satellite by a short boom. The harpoon, shot from the refrigerator-sized satellite at a speed of 44 miles an hour and trailing a tether, slammed into the panel — and stuck to it, as planned.

“We are really happy so far,” said Guglielmo Aglietti, director of the Surrey Space Centre in England and lead investigator of the $15 million project. “The target was made of the same material as a satellite, so it’s quite representative of how the whole thing would work.”

In an actual mission to clean up space junk, a satellite would use a much larger space harpoon to snare debris and then drag it down into the atmosphere, where the entire assemblage would burn up harmlessly. Aglietti likened the maneuver to a kamikaze mission.

From spent rocket parts to defunct satellites to stray nuts and bolts, the U.S. Department of Defense now tracks more than 500,000 pieces of human-made debris that have accumulated in orbit around Earth. All that trash poses a serious and growing collision threat to passing spacecraft, including the International Space Station, as well as satellites that cost billions of dollars.

“Statistically, every five to nine years, we have to expect one so-called catastrophic collision in which a defunct, but still intact, large [piece of] space debris gets hit and fragments into thousands of new fragments,” Manuel Metz, a space debris expert at the German Aerospace Center in Bonn who isn’t involved with the RemoveDebris project, told NBC News MACH in an email Tuesday. “These new fragments might themselves create new collisions and thus a cascading effect might begin” — a potentially disastrous phenomenon known as the Kessler syndrome that was depicted in the 2013 movie “Gravity.”

Aglietti thinks it makes sense to focus initially on removing the biggest pieces of debris because they pose the greatest danger. The idea would be to launch a series of the debris-cleaning satellites and have them capture and eliminate a few pieces each year.

If the ongoing RemoveDebris mission concludes successfully, Aglietti hopes that aerospace companies would be willing to fund the missions to clean up the space junk. "This is a proof of concept," he said. "If it works, we hope our industrial partners will move it forward into a business."

The harpoon demonstration was the second in a series of tests of experimental debris-collecting devices conducted by the RemoveDebris satellite, which was built by a consortium of universities and aerospace companies and was funded principally by the European Union.

Last September, the satellite successfully used a spring-loaded net to capture a piece of mock debris. In March, the satellite will attach an inflatable “drag sail” to a piece of debris -- mission scientists expect the sail to collide with the few air molecules that are present at the satellite’s altitude, slowing the debris and causing it to descend into the atmosphere and burn up.

Various other devices have been proposed for capturing and eliminating space debris, including self-propelled tethers and robotic arms. Aglietti said the harpoon, net and drag sail were chosen for the RemoveDebris project because they were considered especially economical.

Moriba Jah, a space scientist at the University of Texas at Austin and an expert on orbital debris, said it would be good to have more than one way to eliminate all the accumulated junk. "The active removal of space debris will require many different methods and techniques," he said in an email Tuesday. “I believe we need to have a so-called ‘toolkit’ of methods that can be applied as best and appropriate.”

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