NASA is testing several propellant-free propulsion technologies, and one, dubbed ProSEDS, could be used soon.
It is based on a tether and is formally called the propulsive small expendable deployer. The tether is a 3.2-mile ultrathin bare wire attached to a 6.2-mile nonconducting cable. When it is deployed and the tether slices through the Earth's magnetic field, it will induce a current which charges the tether. This attracts more electrons, creating drag, and lowering the satellite's orbit
Plans are to test the device in space this summer. It could be used to take nonfunctioning satellites and other space debris out of orbit without using costly, chemical-based propulsion systems.