Delta IV
Each Delta IV launch vehicle is based on a Common Booster Core (CBC) powered by a Pratt and Whitney Rocketdyne RS-68A engine and a Delta Cryogenic Second Stage (DCSS) powered by an RL10. Delta IV Heavy is distinguished by two additional CBCs and always flies with a 5 m DCSS and payload fairing, while Delta IV Medium flew with two or four SRBs on a single CBC.