CU later, EUS… “NASA must standardize its approach, increase flight rate safely, and execute on the president’s national space policy,” Isaacman said. “With credible competition from our greatest geopolitical adversary increasing by the day, we need to move faster, eliminate delays, and achieve our objectives.” The announced changes to the Artemis program include the cancellation of the Exploration Upper Stage and Block IB upgrade for SLS rocket, and future SLS missions, starting with Artemis IV, will use a “standardized” commercial upper stage. Artemis III will no longer land on the Moon. Instead, the Orion spacecraft will launch on SLS and dock with SpaceX’s Starship and/or Blue Origin’s Blue Moon landers in low-Earth orbit.

NASA favors ULA upper stage. United Launch Alliance’s Centaur V upper stage, used on the company’s Vulcan rocket, will replace the Exploration Upper Stage (EUS) on SLS missions beginning with Artemis IV, Bloomberg reports. ULA, a 50-50 joint venture between Boeing and Lockheed Martin, also built the interim upper stages flying on the Artemis I, II, and III missions. Those stages were based on designs used for ULA’s now-retired Delta IV Heavy rocket. With that production line shut down, ULA will now provide Centaur Vs to NASA. This means Boeing, which was on contract to develop the EUS, will still have a role in supplying upper stages for the SLS rocket. Boeing is also the prime contractor for the rocket’s massive core stage.

Building on a legacy… The Centaur V upper stage is the latest version of a design that dates back to the 1960s. Centaurs began flying in 1962, and the Centaur V is the most powerful variant, with a wider diameter and two hydrogen-fueled RL10 engines. The Centaur V still uses the ultra-thin, pressure-stabilized stainless steel structure used on all Centaur upper stages. The Centaur has a reliable track record, and the Centaur V’s predecessor, the Centaur III, was human-rated for launches of Boeing’s Starliner crew capsule.