Hall thruster operating in a vacuum chamber that simulates the environment of deep space. This is identical to the engine that will propel the Psyche spacecraft that will launch on a mission to the main asteroid belt between Mars and Jupiter in August 2022. The propellant gas, in this case xenon, is ionised and accelerated out of the thruster, creating thrust to propel the spacecraft. The xenon plasma emits a blue glow as the engine operates. Photographed at NASA's Jet Propulsion Laboratory, Pasadena, California, USA, on 20th May 2020.