Space debris, including defunct satellites, chunks of spacecraft, and abandoned rocket stages, is piling up in orbit at an alarming rate. At a conference held this week by the European Space Agency (ESA), researchers suggested various ways to tackle the problem — including harpoons, nets, and junk-busting lasers.

The density of space debris has become so severe, recent research has warned, that a disastrous in-orbit collision could occur every five to nine years. And that estimate is "an optimistic look" modeled on the assumption that most space agencies comply with an agreement to remove their equipment from orbit within 25 years of mission completion. Most notably, potential collisions threaten to interfere with communication and observation satellites.

An estimated 170 million pieces of cosmic trash

So how do you clean up an estimated 170 million pieces of cosmic trash racing through orbit? Some experts, including Thomas Schildknecht, an astronomer who spoke at the ESA conference, suggest deploying a satellite affixed with a net and harpoon to snag unwanted items. Satellites that fire ions in the direction of debris might also succeed in dragging small pieces of junk back towards Earth, and lasers on the ground have the potential to do the same. In the case of bigger objects, it might be necessary to employ "suicide robots" that would be sent into orbit on single missions — each one costing an estimated $200 million.

But that's a small price to pay to protect valuable spots in orbit, said Heiner Klinkrad with the ESA. "Whatever we do is going to be an expensive solution," he noted. "But one has to compare the costs of what we are investing to solve the problem as compared to losing the infrastructure that we have in orbit."

One project, run out of the Swiss Space Center, will soon see "janitor satellites" taking on some of the debris. Unfortunately, most other ideas on space junk removal remain speculative — in part because agencies have yet to agree on who'll fork over the money to execute a comprehensive plan.