NASA has formally awarded a sole-source contract to United Launch Alliance for the upper stage engines that will propel the Orion spacecraft toward the Moon on the Artemis IV and Artemis V missions. The contract was granted without open bidding, according to a Justification for Other Than Full and Open Competition (JOFOC) signed Thursday at Marshall Space Flight Center.

The document, signed March 6 by NASA Senior Procurement Executive Marvin Horne, confirms that ULA’s Vulcan Centaur V upper stage — the same stage that powers ULA’s commercial Vulcan rocket — will replace the long-planned Exploration Upper Stage, or EUS, which had been the intended powerhouse for the Block 1B configuration of the Space Launch System beginning with Artemis IV.

The EUS cancellation effectively means NASA is standardizing on the Block 1 SLS configuration through at least Artemis V, a significant restructuring of the agency’s lunar architecture.

Blue Origin’s New Glenn Upper Stage Was Assessed

The document assessed two candidates: ULA’s Centaur V and Blue Origin’s New Glenn Upper Stage. The NGUS was disqualified primarily on schedule and infrastructure grounds. NASA noted that while the New Glenn upper stage completed a demonstration flight in January 2025 and a second flight in November 2025, it remains in early development phases. Furthermore, NASA stated, adapting it for SLS would require relocating the Mobile Launcher 1 crew access arm, modifying umbilical systems, shortening the stage to clear the Vehicle Assembly Building’s height constraints, and then requalifying the modified vehicle through full-scale testing — a process NASA concluded would blow past the Artemis IV launch readiness window.

The Centaur, by contrast, has a heritage dating to the 1960s, and it shares many commonalities with the Interim Cryogenic Propulsion Stage (ICPS) it is replacing:

Under the planned contract, ULA would deliver two flight units and one flight spare, with the first stage required at Kennedy Space Center no later than nine months prior to the Artemis IV launch, currently targeted for early 2028, and the second no later than L-9 months ahead of Artemis V, planned for late 2028. The estimated period of performance is approximately six years, covering production, integration, and post-flight requirements. The contract value is redacted in the public version of the document.

Timeline and Scope

Under the planned contract, ULA would deliver two flight units and one flight spare, with the first stage required at Kennedy Space Center no later than nine months prior to the Artemis IV launch, currently targeted for early 2028, and the second no later than L-9 months ahead of Artemis V, planned for late 2028. The estimated period of performance is approximately six years, covering production, integration, and post-flight requirements. The contract value is redacted in the public version of the document.

Contract Document