NASA’s wet dress rehearsal—a crucial test of the agency’s Artemis II mission to the moon—hit a snag 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 fast fill and 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,” NASA said in a statement.
On supporting science journalism
If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
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.
It’s Time to Stand Up for Science
If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.
I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.
If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.
In return, you get essential news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-watch videos, challenging games, and the science world’s best writing and reporting. You can even gift someone a subscription.
There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.