NASA's Artemis II wet dress rehearsal ended early on February 2 when liquid hydrogen leaks spiked at the five-minute mark, forcing controllers to scrub the countdown test. The agency announced February 3 it would delay the crewed lunar flyby from February 8 to at least March 6-9 or March 11.
The leak occurred at the interface routing cryogenic propellant into the Space Launch System's core stage. Engineers stopped the hydrogen flow, hoping warming would let seals reseat. They eventually filled both core stage and interim cryogenic propulsion stage tanks, restarted the countdown, then hit the same problem: the ground sequencer automatically halted at T-minus 5:15 when leak rates exceeded limits.
This is the second time hydrogen leaks have derailed an Artemis launch. The first SLS mission in 2022 faced identical issues. Three years and one successful uncrewed flight later, the problem persists.
"Repeating errors is generally frowned upon," a chemical engineer with cryogenics experience told The Register. "You'd think the post-launch review from three years ago might have led with: 'We should probably give that whole hydrogen pissing out all over the place issue a coat of looking at.'"
NASA hasn't confirmed whether the rocket will roll back to the Vehicle Assembly Building or if repairs can happen at Launch Complex 39B. A second wet dress rehearsal is planned before any launch attempt. The crew, in quarantine since January 21, has been released.
Artemis II will send four astronauts on a 10-day lunar flyby, the first crewed U.S. moon mission since Apollo 17 in 1972. The mission has already slipped from late 2024 to September 2025, then April 2026, due to Orion heat shield concerns and life support issues. Available launch windows run through early April, with a final April 30 slot.
Administrator Jared Isaacman called delays expected, noting wet dress rehearsals exist to surface issues when there's been three years between SLS launches. The trade-off: more delays now versus crew safety later. History suggests NASA will take the time it needs, even if the hydrogen problems are starting to sound familiar.