NASA was forced to end a critical fueling test of its giant Artemis 2 rocket early in the wee hours of Tuesday, delaying its mission to launch astronauts around the moon by at least a month. Now that a new day has dawned on the big orange launch vehicle, the space agency is attempting to shed some light on what exactly went wrong — and a lot of what it's saying sounds familiar.
The fueling testfor NASA's Artemis 2 Space Launch System (SLS) rocket began late Saturday (Jan. 31), and ran until Tuesday morning. Called a "wet dress rehearsal," it's a test to put the SLS launch vehicle and ground teams through a simulated countdown clock to fully power-on and fuel the rocket with the more than 700,000 gallons of liquid hydrogen and liquid oxygen it needs to get off the ground.
Tanking operations began smoothly yesterday (Feb. 2) after mission managers polled "go" to begin procedures, but hydrogen leaks detected at the SLS tail service mast umbilical quick disconnect on the launch platform put technicians into a troubleshooting mode most of the afternoon.
If that sounds familiar, it's because the Artemis 1 SLS experienced hydrogen leaks in the same location during its wet dress rehearsal three years ago. Those leaks resulted in three separate rollbacks to NASA's cavernous Vehicle Assembly Building (VAB) over the course of six months before Artemis 1 would finally launch.
Artemis 1 launched in November 2022 and flew an uncrewed Orion spacecraft on a month-long mission to lunar orbit and back.
With Artemis 2, NASA will test Orion's ability to sustain astronauts in deep space. NASA astronauts Reid Wiseman, Victor Glover and Christina Koch, and Canadian astronaut Jeremy Hansen, will ride aboard Orion on a 10-day mission around the far side of the moon. The flight will qualify the spacecraft's systems for Artemis 3, which NASA is planning as the mission to land astronauts back on the lunar surface.
"We really did learn a lot from the Artemis 1 mission, and we implemented a lot of the lessons learned yesterday through wet dress," Lori Glaze, NASA's Exploration Systems Development Mission Directorate acting associate administrator, said during a post-wet dress rehearsal press conference on Tuesday.
"Everyone's aware of some of the challenges with the hydrogen tanking from Artemis 1, and we've made some changes," Glaze said.
To NASA's credit, the Artemis 2 wet dress rehearsal went far smoother than Artemis 1's first fueling test.
Despite the hours of troubleshooting the persistent hydrogen leak — which NASA officials say was stabilized within acceptable limits (but never eliminated) —mission operators managed to fully fuel both SLS stages and carry the test down to the simulated clock's terminal count (the last 10 minutes before liftoff). But the team didn't quite get as close to T-0 as needed in order to earn NASA's gold stamp of approval to launch with a crew onboard.
"The fact that we got to full tanking yesterday on the first try was a tremendous success, and we gathered an enormous amount of data in the processes and how we want to go forward with that in the future," Glaze said.
At T-5 minutes 15 seconds, the SLS ground launch sequencer terminated the count due to a spike in the same quick disconnect hydrogen leak it had experienced all afternoon, which was cause to abort the test, NASA said.
"As we began that pressurization, we did see that the leak within the cavity came up pretty quick," Artemis Launch Director Charlie Blackwell-Thompson said during Tuesday's press briefing, referring to a cavity on the rocket's mast umbilical. The activity triggered safety procedures already in place for such contingencies, she added.
"We got into our safety steps. We saw the hydrogen concentration come down and then later in the evening, we got into our drain operation," she said.
While maintaining the wet dress rehearsal an overall success in terms of data gathered and the accolade of filling SLS's tanks on the first try, Blackwell-Thompson also assured that, unlike Artemis 1, the hydrogen hiccups can likely be addressed at the pad, and don't seem to warrant a rollback to the VAB for maintenance.
"During Artemis 1, we found out that we can do some work on these plates at the pad," Blackwell-Thompson said. "I had hoped that we would not have to demonstrate that again for Artemis 2, but we showed that we can go do this work at the pad and be ready for launch."
As for why SLS is still experiencing these same hydrogen leaks after three years between missions, NASA officials have some theories, but haven't quite nailed down a definitive cause. "These are very bespoke components," NASA Associate Administrator Amit Kshatriya said Tuesday, describing each SLS as its own unique vehicle to learn and understand.
The leaky seal could possibly be a result of vibrations incurred during the rocket's initial rollout to the pad,, Kshatriya said. It took the Artemis 2 SLS rocket nearly 12 hours to make the 4-mile trip to the pad from the VAB at a top speed of 1 mile an hour last month.
"That rollout environment is very complicated," he added, noting that the Artemis 1 SLS was put through different acceleration tests on its way between the VAB and the pad at Launch Complex-39B specifically to help determine the effect of such stresses on the rocket and launch platform. "We think that's a contributor. But again, we have to tear the seal apart and see what happened."
"This is the first time this particular machine has borne witness to cryogens. And how it breathes, and how it vents, and how it wants to leak is something we have to characterize," Kshatriya said, and testing before the launch pad can only go so far.
Even with an "aggressive approach" to dealing with hydrogen leaks during Artemis 1, "we're pretty limited as to how much realism we can put into the test," said John Honeycutt, the chair of NASA's Artemis Mission Management team. "We try to test like we fly, but this interface is a very complex interface, and when you're dealing with hydrogen, it's a small molecule, it's highly energetic," he said, admitting he and mission managers weren't expecting these issues to crop up again.
"This one caught us off guard," Honeycutt added. "The initial things that we were seeing in the technical team felt like we either had some sort of misalignment or some sort of deformation or debris on the seal."
With the conclusion of the wet dress rehearsal today, we are moving off the February launch window and targeting March for the earliest possible launch of Artemis II.With more than three years between SLS launches, we fully anticipated encountering challenges. That is precisely…February 3, 2026
NASA needs to evaluate the rocket and ground infrastructure at the pad before determining the next possible date to attempt another wet dress rehearsal, and has opted to forgo Artemis 2's February launch opportunity, which, had the test gone successfully, spanned from Feb. 8-11.
"With more than three years between SLS launches, we fully anticipated encountering challenges," NASA Administrator Jared Isaacman said in a post on X early Tuesday. "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."
Mission managers are now targeting next month's window, which is open March 6-9 and March 11, with about five days available around the first week of each month thereafter.
