The active gases used in the Soviet plasma propulsion engines were argon and helium.

"They have cut off the plasma propulsion engine and are using an artificial gravitation field to float down as gently as a falling leaf."

A plasma propulsion engine is a type of Ion thruster which uses plasma in some or all parts of the thrust generation process.

In December 2008 NASA signed an agreement with the Ad Astra Rocket Company which may result in the testing on the ISS of a VASIMR plasma propulsion engine.

Although current orbit insertion maneuvers require precisely timed burns of conventional chemical rockets, some headway has been made towards the use of alternative means of stabilizing orbits, such as ion thruster or plasma propulsion engine to achieve the same result using less fuel over a longer period of time.