CAPE CANAVERAL—NASA plans to switch contractors to supply the upper stage for its Space Launch System (SLS) Moon rocket from the Boeing-built Exploration Upper Stage to United Launch Alliance’s (ULA) Centaur V.

The switch was formally unveiled in a document posted March 6 on NASA’s procurement website outlining the agency’s rationale to issue ULA a non-competed, sole-source contract. The value of the contract, which covers two flight units and a spare, was not disclosed.

NASA Administrator Jared Isaacman and managers of the agency’s Artemis lunar human exploration program announced Feb. 27 its plan to cancel SLS upgrades as part of a revised plan to standardize its configuration to help improve its flight rate to 10-12 months between launch campaigns from the current 3 1/2-year cycle.

NASA had planned to use the Boeing Exploration Upper Stage beginning with Artemis III in 2028. Audits by the U.S. Government Accountability Office and the NASA Office of Inspector General estimated the agency would spend close to $3 billion on the program before its first flight.

Cost estimates to switch to ULA’s Centaur V, which flies on the company’s Vulcan rockets, were not released.

NASA is looking to have the first SLS Centaur V in hand nine months before it plans to land astronauts on the Moon in early 2028, a mission that is now earmarked for Artemis IV. In addition to standardizing SLS design, Isaacman unveiled plans to add another flight test in low Earth orbit (LEO) to demonstrate one or both of the crewed lunar landing systems in development ahead of Artemis IV.

SLS currently flies with an upper stage provided by ULA that is based on the upper stage that flew on its now-retired Delta IV Heavy rockets.

The second SLS, outfitted with ULA’s Interim Cryogenic Propulsion Stage (ICPS) is being prepared for a launch in April to test an Orion spacecraft with crew. Artemis II is expected to become the first human spaceflight beyond low Earth orbit since the final Apollo Moon mission in 1972.

The third and final ICPS is earmarked for the newly added mission in LEO, now known as Artemis III, to test Human Lander Systems being developed by SpaceX and Blue Origin.

In a Justification for Other Than Full and Open Competition document, NASA said its approach “leverages current support infrastructure and will use, with relatively minor modifications, an existing ULA upper stage. All other alternative solutions fail to meet the performance requirements, would require significant modifications to hardware that is still under development, or would require the development of new hardware that does not currently exist.

“When the design parameters and performance characteristics of the potential sources were compared against SLS upper stage design parameters and performance characteristics, only the Centaur is capable (with relatively minor modifications) of meeting the requirements of the government,” NASA wrote.

The agency also considered the liquid-hydrogen- and liquid-oxygen-fueled upper stage flying on Blue Origin’s New Glenn, but determined that vehicle, the BE-3, would require significant modifications to use fuel and oxidizer commodity infrastructure at the SLS launchpad and other SLS assets. “For example, using the New Glenn upper stage would require relocating the Mobile Launcher Crew Access Arm and modification to the upper stage umbilical retraction mechanism,” NASA added. “The stage could be shortened to meet Vehicle Assembly Building height constraints, but would require full-scale development and testing to qualify the stage for the shorter configuration.

“Full-scale testing/requalification would result in unacceptable schedule impacts and additional cost risk to the SLS Program,” the agency concluded.

NASA stipulated the ICPS replacement must comply with human-rating requirements and have a lift capacity of about 60,000 lb., and a delta-V greater than 3,050 m/s with three engine ignitions. NASA also wants the stage to be able to separate and have three-axis control after orbit insertion, but before separation of the Orion capsule. The upper stage also must fit with the SLS core stage, Orion capsule and Orion’s Launch Escape System so that the entire stack can clear the VAB doors.