Commercially-developed liquid hydrogen booster engine providing nearly 700,000 pounds of thrust.
Pratt & Whitney Rocketdyne's RS-68 engine was designed for the Delta IV family of evolved expendable launch vehicles (EELV) with a liquid-hydrogen and oxygen booster. The bell-nozzle RS-68 design permits a drastic reduction in part count (compared with current cryogenic engines) which directly translates to lower development and production costs.