NASA Swaps SLS Upper Stage for Centaur V
NASA is ditching the delayed SLS upper stage in favor of United Launch Alliance’s Centaur V for Artemis missions. The move aims to avoid further schedule slips by using proven propulsion hardware. This highlights the importance of reliability and supply-chain management in major aerospace projects.
NASA's switch to the Centaur V impacts Artemis missions IV and V, both planned for 2028. The Centaur V is already in service as the upper stage for ULA's Vulcan rocket, which has flown four times since its debut in January 2024. NASA also intends to order a flight spare. The original plan called for the Exploration Upper Stage (EUS) on the SLS Block 1B. The EUS would have enabled delivery of up to 11 metric tons more mass to the lunar surface compared to the Block 1. The SLS Block 1B was intended to launch on Artemis IV. NASA justified the sole-source contract to ULA by stating that other options would require significant modifications to Mobile Launcher 1. They also cited ULA's familiarity in modifying upper stages for the SLS. The Atlas Centaur has been used in the Commercial Crew Program, meaning human-rating the Centaur V should be less challenging. The Centaur V uses two RL10 engines from Aerojet Rocketdyne, fueled by liquid hydrogen. NASA also stated that using the Centaur V leverages existing support infrastructure. The agency needs the upper stage nine months before launch for processing at Kennedy Space Center, a timeline other options couldn't meet. The switch to the Centaur V means NASA will standardize the SLS on the Block 1 configuration. NASA will no longer pursue development of the EUS. The initial SLS missions use the Block 1 configuration with the Interim Cryogenic Propulsion Stage (ICPS). The ICPS is a modified Delta IV cryogenic second stage, also built by ULA. NASA is increasing its cadence of Artemis missions, aiming for at least one surface landing per year. Artemis II, a crewed lunar flyby mission, is scheduled for April 2026.
