NASA Faces Hydrogen Leak in Final SLS Rocket Dress Rehearsal For Lunar Mission

NASA encountered a hydrogen leak on Monday during a critical fuelling test of its Space Launch System (SLS) rocket, a key step toward sending astronauts on the first crewed lunar mission in more than 50 years. The issue emerged as engineers loaded the massive rocket with super-cold liquid hydrogen and oxygen during a full-scale countdown rehearsal at the space agency’s Florida launch site.

The launch team began fuelling the 322-foot (98-metre) rocket around midday, aiming to pump more than 700,000 gallons (2.6 million litres) of propellant into its tanks and hold it there for several hours. The test, known as a wet dress rehearsal, is designed to mirror the final stages of an actual launch countdown and is considered a make-or-break milestone for setting a launch date.

A few hours into the operation, sensors detected excessive hydrogen near the bottom of the rocket, prompting officials to temporarily halt hydrogen loading with only about half of the core stage filled. Engineers immediately began troubleshooting, applying techniques developed during the SLS rocket’s first uncrewed test flight three years ago, which was also delayed multiple times by hydrogen leaks.

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The four-member crew assigned to the mission—three Americans and one Canadian—monitored the rehearsal remotely from NASA’s Johnson Space Center in Houston. The astronauts have been in quarantine for more than a week as they await the outcome of the test, which will determine whether the mission can proceed on schedule.

NASA is already running behind after a recent cold snap delayed preparations by two days. If the fuelling test is completed successfully, the agency could attempt a launch as early as Sunday. However, the rocket must lift off by February 11, or the mission will be postponed until March due to limited monthly launch windows.

The nearly 10-day mission will send the crew past the Moon and around its far side before returning to Earth, without entering lunar orbit or attempting a landing. The flight is part of NASA’s Artemis programme, which aims to establish a sustained human presence on the Moon and pave the way for future crewed landings.

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