The RS-68 engine is the first new large liquid-fueled rocket engine to be developed in the United States in 25 years. Designed for the Boeing Delta IV family of evolved expendable launch vehicles (EELV), the bell-nozzle RS-68 is a liquid hydrogen - liquid oxygen booster engine utilizing a simplified design philosophy resulting in a drastic reduction in parts compared to current cryogenic engines. This design approach results in lower development and production costs.