Glossary / Space
Ion engine
A thruster that ionises a gas such as xenon and accelerates it electrically to high speed. Its thrust is tiny, but it uses propellant extremely efficiently.
Chemical rockets expel gas at a few kilometres per second; an ion engine manages around 30. By the rocket equation, the same propellant then buys a far larger change in velocity. The thrust, though, is about the weight of a sheet of paper, so the engine fires for months or years.
NASA's Deep Space 1, launched in 1998, demonstrated one as primary propulsion in deep space[1]. Japan's Hayabusa made its round trip to an asteroid with its own ion engines, which ionise gas using microwaves.
Related terms
- Rocket equationThe equation stating that a rocket's gain in speed depends on its exhaust velocity and on the ratio of its starting mass to its burnt-out mass.
- Gravity assistUsing a planet's gravity and orbital motion to change a spacecraft's speed or direction without fuel as it flies past.