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There are now an estimated 30,000 large pieces of space debris orbiting the earth - everything from old rocket casings to bolts blown from hatches during space missions.

All these are orbiting the earth at high speed and could put a satellite out of action in any collision. Astronauts are being advised to only carry out any spacewalks when it is absolutely essential because of the risks.

There are also concerns that a single collision could casue a chain reaction - as featured in the movie Gravity - where space junk shatters and pieces fly around shattering ever more debris and working satellites.

So what can be done? Scientists in Australia are looking into the possibility of cleaning up space by using lasers and robotic spacecraft that could bring the debris back down to earth.

Spencer Kelly finds out more.