NASA Shifts SLS Strategy: Centaur 5 to Power Artemis Missions
In a significant move to streamline its ambitious Artemis program, NASA has officially selected United Launch Alliance’s (ULA) Centaur 5 as the upper stage for the Space Launch System (SLS) rocket, beginning with the Artemis 4 mission, slated for launch no earlier than early 2028. This decision marks a departure from previous plans involving the Exploration Upper Stage (EUS) and reflects a broader effort to reduce complexity and accelerate launch rates.
From Theoretical Change to Reality
The shift comes after NASA Administrator Jared Isaacman announced a move towards a “standardization of the [Space Launch System rocket] fleet to… a near-Block 1 configuration.” The goal, as Isaacman explained, is to “reduce complexity to the greatest extent possible,” accelerate manufacturing, and enhance safety through increased launch frequency. Interestingly, ULA President and CEO Tory Bruno anticipated this possibility back in December 2024, acknowledging the company’s readiness to adapt to changes in the SLS architecture.
Why Centaur 5? A Proven Performer
The Centaur 5 has already demonstrated its reliability as the upper stage for ULA’s Vulcan rocket, successfully completing four flights since its debut in January 2024. NASA’s decision was formalized in contract documents published on March 6, 2026, and is being pursued as a sole-source contract with ULA. Several factors contributed to this choice, including the Centaur 5’s compatibility with existing infrastructure at the Kennedy Space Center, specifically Mobile Launcher 1, and its utilization of liquid oxygen and liquid hydrogen – the same propellants used by the SLS.
The agency likewise highlighted the Centaur’s heritage, stemming from the RL10 engine which has a long track record of successful operation. The Centaur 3 stage’s certification for human spaceflight under the Commercial Crew Program provided a foundation of confidence in the Centaur 5’s capabilities.
The Fate of the Exploration Upper Stage
Originally, NASA envisioned the EUS, built by Boeing, as the upper stage for Artemis 4 and subsequent missions. Though, a 2024 report from NASA’s Office of Inspector General revealed significant cost and schedule overruns with the EUS development. The report projected costs reaching approximately $5.7 billion by 2028, a $700 million increase from previous estimates. Quality control issues at the Michoud Assembly Facility in Louisiana were also cited as contributing factors to the delays.
The EUS was designed to deliver significantly more mass to the lunar surface – up to 11 metric tons more than the current Interim Cryogenic Propulsion Stage (ICPS) – enabling “more ambitious missions.” However, the escalating costs and delays prompted NASA to reassess its strategy.
Blue Origin’s Novel Glenn Stage Considered, But Ultimately Passed Over
While Blue Origin’s New Glenn stage was considered as a potential alternative, NASA ultimately determined it would require substantial modifications to both the stage itself and the existing ground infrastructure at the Kennedy Space Center. Specifically, relocating the Mobile Launcher Crew Access Arm and modifying the upper stage umbilical retraction mechanism would have been necessary. These modifications, along with the need for extensive testing and re-qualification, were deemed unacceptable due to schedule and cost implications.
A Focus on Standardization and Safety
This decision underscores NASA’s commitment to streamlining the SLS program and prioritizing safety. By standardizing on a near-Block 1 configuration with the Centaur 5, the agency aims to accelerate launch rates and reduce the risk of delays associated with complex new hardware development. The move is also expected to lower overall program costs.
Did you know?
The Centaur upper stage has been a workhorse of space launch for decades, with the first Centaur stage flying in 1963.
FAQ
Q: What is the Artemis program?
A: The Artemis program is NASA’s effort to return humans to the Moon and establish a sustainable presence there, paving the way for future missions to Mars.
Q: What is the SLS rocket?
A: The Space Launch System (SLS) is a super heavy-lift launch vehicle being developed by NASA to support the Artemis program.
Q: What is the Centaur 5?
A: The Centaur 5 is an upper stage developed by United Launch Alliance (ULA) for its Vulcan rocket. It will now also be used for the SLS.
Q: Why did NASA cancel the Exploration Upper Stage (EUS)?
A: The EUS experienced significant cost and schedule overruns, leading NASA to seek a more cost-effective and readily available alternative.
Q: What are the benefits of using the Centaur 5?
A: The Centaur 5 is a proven performer, compatible with existing infrastructure, and offers a faster path to increased launch rates.
Pro Tip: Keep up with the latest Artemis program updates on NASA’s official website: https://www.nasa.gov/artemisprogram/
Explore more about the SLS rocket and its components here.
