reaction engine

His system is, as the firm’s name implies, a reaction engine.

Out of the port they could see the red flare of a reaction engine; the next ship in their sector, speeding forward.

This also was the invention of Hero, and was a reaction engine, on the principle of the eolipile.

Broadly, reaction engines come in two varieties—rockets and jets—in which hot gases created by burning fuel are ejected out of the back, providing the action part of the law.