NASA has selected United Launch Alliance’s Centaur V upper stage for the Artemis missions that aim to return astronauts to the lunar surface for the first time since 1972.

The space agency will use the Centaur V, currently flying as the upper stage of ULA’s Vulcan rocket, for Artemis IV and V, both slated for 2028. A flight spare is also being ordered.

The Interim Cryogenic Propulsion System (ICPS) currently used by Artemis is a modified Delta IV cryogenic second stage, always intended as a stopgap. NASA had planned to replace it with the more powerful Exploration Upper Stage (EUS) but that program is running behind schedule and over budget. When new administrator Jared Isaacman signalled plans to increase SLS flight cadence, the writing was on the wall leaving Centaur V to fill the gap.

ULA is not the only upper stage option, and NASA’s intention to issue a sole-source contract might surprise some. However, the agency noted that alternatives, such as Blue Origin’s New Glenn Upper Stage (NGUS), require “significant modifications” to Mobile Launcher 1, and ULA was already familiar with the steps needed to modify an upper stage for SLS. In addition, the Centaur V is a variant of the Atlas Centaur, used under the Commercial Crew Program, meaning that qualifying the stage for a human crew should not cause too many concerns.