NASA has removed one of its main engines from the Space Launch System (SLS) rocket bound for the Artemis II mission, which will send four astronauts on a lunar voyage next year. The decision comes after a hydraulic leak was discovered in the engine’s oxidizer valve actuator.
To address the issue, technicians replaced the defective engine with another one from NASA’s inventory and are now integrating it into the rocket’s core stage. This is the first time a main engine has been replaced on the SLS core stage.
The replacement will not affect the mission timeline, as the repaired engine will be ready for future use. The Artemis II mission, scheduled for early 2026, will mark the first human flight to the far side of the Moon since the final Apollo lunar mission in 1972.
Source: https://arstechnica.com/space/2025/04/nasa-just-swapped-a-10-year-old-artemis-ii-engine-with-one-nearly-twice-its-age