A reaction engine that contains all the substances necessary for its operation and is not dependent on substances such as atmospheric oxygen, drawn from the surrounding medium, and thus is capable of operating in outer space.
A reaction engine carrying its liquid fuel and liquid oxidizing agent in separate tanks: the fuel and oxidizer are brought together and ignited in a combustion chamber to create hot, explosive gas that escapes through a nozzle, providing a powerful thrust.
An engine used to produce a jet of hot gases to propel a rocket. The jet is produced by combustion of a fuel with other chemicals stored in the rocket. Since they do not rely on the oxygen in the atmosphere for combustion, rocket engines can operate in space.