NASA encountered a setback during the Artemis II wet dress rehearsal on Monday when engineers detected signs of a hydrogen leak, forcing a temporary pause in fueling operations at Kennedy Space Center.
The wet dress rehearsal is a comprehensive countdown simulation designed to validate every step of launch-day procedures, from loading cryogenic propellants into the Space Launch System (SLS) rocket to running through the final countdown sequence. It represents one of the last major milestones before the agency can clear the mission for flight.
As ground crews loaded liquid hydrogen and liquid oxygen into the SLS core stage and upper stage, sensor readings indicated several possible leaks in the hydrogen system. NASA made the decision to halt the flow of liquid hydrogen into the core stage — the massive first-stage booster that powers the rocket’s four RS-25 engines — while technicians assessed the situation.
Liquid oxygen operations were unaffected and continued without interruption throughout the troubleshooting period. Engineers also temporarily suspended hydrogen loading into the Interim Cryogenic Propulsion Stage (ICPS), the upper stage responsible for propelling the Orion spacecraft toward the Moon.
After evaluating the data, NASA gave the go-ahead to resume hydrogen fueling. Teams then worked to complete the fast-fill and topping procedures while monitoring hydrogen concentration levels to ensure they remained within safe operating parameters.
Hydrogen-related issues are not new to the Artemis program. The Artemis I campaign experienced similar leak concerns during its own wet dress rehearsal and tanking attempts in 2022, which led to multiple scrubs and weeks of delays before the rocket finally launched in November of that year. The recurrence of these challenges highlights the difficulty of handling super-cooled cryogenic hydrogen, which is notoriously prone to seeping through seals and fittings due to its extremely small molecular size.
Artemis II is set to be a landmark achievement in human spaceflight. The mission will carry four astronauts — Commander Reid Wiseman, Pilot Victor Glover, Mission Specialist Christina Koch, and Canadian Space Agency astronaut Jeremy Hansen — on an approximately 10-day voyage around the Moon, marking the first crewed lunar flyby since Apollo 17 in 1972. Successful completion of the wet dress rehearsal would keep the mission on track for its targeted launch date of no earlier than February 8, 2026.
