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.
And then there’s time. According to NASA’s justification for the decision: “The NASA Kennedy Space Center (KSC) need date for processing is projected to be nine months prior to a launch. Award to another source would cause unacceptable delays to current launch schedules.”
Isaacman announced a shake-up of the delay-plagued, cost-bloated NASA’s Artemis program at the end of February. Under the revised plan, Artemis III becomes an Apollo 9-style shakedown of the human landing system in Low Earth Orbit in 2027, pushing the first lunar landing attempt back to Artemis IV in 2028.
One casualty of the reshuffle was the EUS. Industry watchers had widely expected Centaur V to step into the breach, not least because NASA had, perhaps inadvertently, rather given the game away by including imagery of the stage in materials released at the time.
However, swapping upper stages solves only part of Artemis’s problems. The bigger challenge remains the Human Landing System as NASA still needs a version ready for a Low Earth Orbit checkout next year, with an actual lunar landing to follow in 2028. Sorting out the SLS’s upper stage is all well and good, but it does nothing to address the elephant that may or may not end up on the Moon. ®