The team came up with a way to use the breakdown of debris as a source of fuel. Pieces that are less than 10cm (approximately four inches) in size are caught in a net and then passed through a ball mill. This is a rotating cylinder that pulverizes the junk into a fine powder. It is then heated and passed through a system that sorts out the positive from the negatively charged ions. The positive are pushed through an electric field which increases their overall energy, generating thrust, while the negative are expelled into the surrounding space.

What's unclear, though, is how the spacecraft will run. MIT Technology Review notes that yes, the craft won't need a propellant, but it needs a power source for the ball mill to run. The team stated that the craft can use a combination of solar and nuclear power, but didn't really go into what the safety implications are from having a nuclear-powered object orbiting Earth.

[Image credit: HENDRIK SCHMIDT/AFP/Getty Images]