In this interactive activity adapted from NASA, learn about ion engines. Review how subatomic particles have electric charge and how atoms become ions. Learn about the components of an ion engine (including fuel, cathode emitters, a screen grid, and an accelerator grid) and explore how it produces thrust for a spacecraft. Using a simulation of an ion engine, manipulate the distance between grids and the difference in charge between grids to see how they affect the total impulse. An image gallery provides information about the Dawn spacecraft, which uses an ion engine.