A steam rocket (also known as a hot water rocket) is a thermal rocket that uses water held in a pressure vessel at a high temperature, such that its saturated vapor pressure is significantly greater than ambient pressure. The water is allowed to escape as steam through a rocket nozzle to produce thrust.[1]
Steam rockets are usually pressure fed, but more complex designs using solar energy or nuclear energy have been proposed. They are probably best known for their use in rocket-powered cars and motorcycles, and they are the type used in aeolipile.