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NASA Formally Cancels Exploration Upper Stage, Switches to ULA Centaur V for SLS Artemis IV+

Canopy Hardware
Illustration of the NASA Exploration Upper Stage with a witch hat representing its cancellation and replacement with ULA Centaur V

NASA issued a sole-source notice on a government procurement site formally cancelling the Exploration Upper Stage (EUS) developed by Boeing and replacing it with United Launch Alliance's commercial Centaur V upper stage for SLS missions from Artemis IV onward. The EUS program received more than $3.5 billion in funding over a decade yet remains years from flight-ready status, making it one of the most expensive and prolonged developments in NASA's recent history. The cancellation is the definitive end of a program that failed to advance Artemis's Moon landing timeline and which consumed resources that could have funded multiple commercial alternatives.

Key Takeaways

  • NASA issues sole-source Centaur V contract to ULA to replace Boeing's Exploration Upper Stage on SLS Artemis IV and Artemis V — formal procurement notice posted March 6, 2026\n· EUS program received $3.5B+ over 10 years (initial Boeing contract $962M; launch tower alone heading past $2B); uses off-the-shelf RL-10 engines that have flown for six decades — still not flight-ready\n· Centaur V (already flying on Vulcan) uses LH2/LOX propellant matching the SLS core stage; switch expected to cut costs and reduce launch cadence pressure on Starship and Blue Moon cryogenic refueling timelines

Original source: Ars Technica