The European Space Agency (Esa) says initial testing of a new plasma drive for spacecraft has been a success.

The "double layer thruster" is a new kind of ion drive which could give much more power than existing versions.

It works by accelerating charged particles between two layers of argon plasma, gas where the atoms have been stripped of electrons.

Esa says it has "proven the principle", and will proceed with simulations and perhaps bigger prototypes.

Esa already uses an ion drive on its Smart 1 Moon probe, and the US space agency Nasa deployed one on Deep Space 1, which flew out to Comet Borrelly in 2001.