NASA’s wet dress rehearsal—a crucial test of the agency’s Artemis II mission to the moon—hit a snag on Monday.
Engineers had been fueling the mission’s Space Launch System (SLS) rocket up with liquid hydrogen and liquid oxygen propellant and planned to initiate a countdown sequence to simulate the launch. But hours into the process, NASA engineers had to temporarily stop the flow of liquid hydrogen into the core stage of the SLS, which houses the rocket’s main engines, to investigate and troubleshoot several potential leaks.
NASA said it had resumed fueling a short time later. “Engineers will attempt to complete filling and then begin topping off the tank. Should that be successful, they will attempt to manage the hydrogen concentration, keeping it within acceptable limits during core stage hydrogen loading,” the agency said in a statement.
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Liquid oxygen (the other main component of the rocket’s fuel) was still flowing into the core stage throughout the issue. As part of the troubleshooting effort, NASA also temporarily paused liquid hydrogen loading into the upper stage, which was designed to loft the Orion crew capsule toward its orbital journey around the moon.
Fuel leaks also plagued the predecessor to Artemis II in testing and held up the launch of that mission, Artemis I, for weeks.
Artemis II will see four astronauts fly a 10-day loop around the moon and back to Earth, a journey that will take them farther into space than any human has gone before. If the wet dress rehearsal is a success, then the mission will launch no earlier than February 8.
Editor’s Note (2/2/26): This is a developing story and will be updated.