A Cesium Ion Rocket Engine
This small contact ion engine produces .0009 kilogram (.002 pound) of thrust by passing vaporized cesium through hot tungsten. On Earth this amount of power is scarcely enough to lift a one-carat jewel an inch off a table, but in the frictionless vacuum of space, it is sufficient to provide attitude control for satellites. It can also accelerate a spacecraft to high interplanetary velocities by operating continuously for thousands of hours.
An ion engine of this type was first tested in space in 1964. On that occasion, it provided .0009 kilogram (.002 pound) of thrust for 2 hours, 10 minutes. It was able to control the attitude of the attached instrument package.
This ion engine is a gift from Electro-Optical Systems, Inc., the company that developed it.