The RL-60 cryogenic upper stage engine is currently under development by Pratt & Whitney of West Palm Beach, Florida.  It is a new design but follows in the footsteps of the RL-10, which was developed in the late 1950's and powers the Centaur upper stage.  The company is projecting that this advanced engine will be available in 2003 for several different launch vehicles.   

The RL-60 expander cycle engine will be approximately the same size as the RL-10, allowing for direct substitution with minimal vehicle modifications.  The engine will produce 50,000 to 65,000 pounds of thrust with a specific impulse above 470 seconds.  Pratt & Whitney is designing the RL-60 engine to meet the needs of current and future launch vehicles and payloads.