A key countdown rehearsal for NASA’s first crewed Artemis mission around the Moon was cut short early Tuesday after engineers were unable to resolve an out-of-limits hydrogen leak, prompting the space agency to formally slip the long-awaited flight from February to no earlier than March.
With the wet dress rehearsal now complete, NASA Administrator Jared Isaacman confirmed that the agency is standing down from its February launch window. “We fully anticipated encountering challenges,” Isaacman said in a post on X. “That is precisely why we conduct a wet dress rehearsal. These tests are designed to surface issues before flight and set up launch day with the highest probability of success.” He added that NASA now plans to conduct an additional full fueling test before targeting a March liftoff.
Credit: NASA/Sam Lott
The Artemis II mission will carry four astronauts — commander Reid Wiseman, pilot Victor Glover, mission specialist Christina Koch, and Canadian Space Agency astronaut Jeremy Hansen — on a roughly 10-day journey around the Moon and back to Earth. The crew had been in pre-flight medical quarantine at Johnson Space Center and was expected to travel to Florida this week to begin final launch preparations. Following the delay, NASA said the astronauts will remain in Houston and rejoin family, friends, and colleagues while engineers work through the issues.
The practice countdown began Saturday evening at Kennedy Space Center, after frigid Space Coast weather pushed the start of operations back by two days. Following a readiness review Monday morning, Launch Director Charlie Blackwell-Thompson authorized teams to begin the remotely controlled fueling of the Space Launch System rocket.
Loading operations started about 45 minutes behind schedule but initially progressed smoothly as super-cooled liquid oxygen and liquid hydrogen were pumped into the rocket’s massive first-stage tanks. Trouble emerged once the first-stage hydrogen tank reached about 55 percent capacity, when sensors detected a leak at a tail service mast umbilical — the plate where ground fuel lines connect to the base of the rocket. Engineers paused fueling, attempted corrective steps, and briefly resumed flow, but the leak reappeared as the tank approached roughly 77 percent full.
NASA said teams attempted to mitigate the issue by halting hydrogen flow, allowing hardware to warm so seals could reseat, and adjusting propellant flow rates. Those steps ultimately allowed the rocket to reach “stable replenish,” a steady state in which tanks are kept topped off. A five-member closeout crew was then sent to the pad to prepare the Orion spacecraft for a simulated crew arrival and to close and test its hatches.
The countdown, originally planned to simulate a 9 p.m. Eastern launch, stretched deep into the night as teams worked through the hydrogen leak, communications dropouts, and other technical issues. After holding at T-minus 10 minutes for an extended period, the count resumed shortly after midnight. It was halted for the final time at T-minus five minutes and 15 seconds when the automated Ground Launch Sequencer detected an increase in the leak and stopped the clock.
“The team will fully review the data, troubleshoot each issue encountered during WDR, make the necessary repairs, and return to testing,” Isaacman said. NASA now expects to perform another wet dress rehearsal before attempting launch again, with five opportunities available in March between March 6 and March 11.
The Space Launch System is the most powerful operational rocket ever built, standing 332 feet tall and generating 8.8 million pounds of thrust at liftoff from two solid rocket boosters and four liquid-fueled core engines. Its only flight to date was the uncrewed Artemis I mission in 2022, a campaign that was itself marked by hydrogen leaks and unexpected propellant behavior that delayed launch for months.
Ahead of this second flight, NASA implemented multiple upgrades and procedural changes based on lessons learned during Artemis I. Blackwell-Thompson said last week she was confident those improvements would lead to a smoother test. Many of the fixes performed as intended during the rehearsal, but leakage at the tail service mast umbilical — a known trouble spot during the 2022 campaign — once again proved to be a limiting factor.
With additional testing now planned, NASA officials say the data gathered during this week’s rehearsal will be critical to clearing the way for the agency’s first crewed mission beyond low Earth orbit in more than half a century.
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