Administrator Jared Isaacman said Friday that launch teams made "major progress" between the first countdown rehearsal, which was disrupted by hydrogen leaks earlier this month, and the second test, which was completed without significant seepage on Thursday night.
The test was "a big step toward America's return to the lunar environment," Isaacman said on the social media platform X.
NASA could launch four astronauts on the Artemis II lunar fly-around as soon as March 6 from Florida's Kennedy Space Centre.
To keep their options open, the three Americans and one Canadian plan to go into the mandatory two-week health quarantine on Friday night.
The space agency has only five days in March to launch the crew aboard the Space Launch System rocket, before standing down until April.
February's opportunities evaporated after dangerous amounts of liquid hydrogen leaked during the first fuelling demonstration.
Technicians replaced two seals, leading to Thursday's successful re-run.
The countdown clocks went all the way down to the desired 29-second mark.
The fixes worked, but there's still pending work, including conducting a flight readiness review, said NASA's Lori Glaze.
Commander Reid Wiseman and two of his crew monitored Thursday's operation alongside launch controllers.
The astronauts will be the first to fly to the moon since Apollo 17 closed out NASA's first chapter in moon exploration in 1972.
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