For the SLS upper stage, NASA could look to flight-proven hardware to get the spacecraft and its Service Module to low-Earth orbit and on to the Moon. Trade studies of existing second stages available resulted in the selection of the Delta IV Cryogenic Second Stage powered by a single Rocketdyne RL10 engine burning: LH2 and LOX. Performance studies determined this stage would need a larger capacity LH2 propellant tank. NASA identified this upper stage as the Interim Cryogenic Propulsion Stage to be used for the early Artemis missions. For human missions to Mars or other destinations with spacecraft having greater mass, NASA proposed the Exploration Upper Stage. It would be powered by four Rocketdyne RL10 engines. NASA selected United Launch Alliance (ULA) to design, develop, and manufacture the ICPS and the EUS.