To better understand how Knievel’s rocket was propelled, according to a listing for “steam rocket” posted on Wikipedia, water, while under pressure, is heated up to a high temperature (approx. 250-500 °C, 2.5 to 5 times the temperature of boiling water). As the hot water goes through the nozzle and the pressure reduces, the water flashes to steam pressing on the nozzle, and leaving at high speed. By the recoil, or opposite action, the rocket accelerates in the opposite direction to the steam. The nozzle of hot water rockets must be able to withstand high pressure, high temperatures and the particularly corrosive nature of hot water.