A hydrogen leak stopped the first attempt cold. Now repairs are done and four astronauts are waiting to find out when they’re going to the moon
The last time NASA tried this, a hydrogen leak shut everything down early and wiped out an entire month of launch opportunities. That was Feb. 2. Since then, engineers replaced seals, replaced a filter, ran a partial fueling test and found more things to fix along the way — because that is, apparently, just how rocket science goes.
- A hydrogen leak stopped the first attempt cold. Now repairs are done and four astronauts are waiting to find out when they’re going to the moon
- What a wet dress rehearsal actually involves
- What NASA is watching most closely
- The crew waiting on the other side of this test
- Why this rehearsal matters beyond Thursday
On Thursday, NASA is trying again. The agency is conducting a second wet dress rehearsal of its Space Launch System rocket at Kennedy Space Center in Florida, a critical test that must go smoothly before a launch date can be set for Artemis II — the mission that will send four astronauts around the moon for the first time since 1972.
What a wet dress rehearsal actually involves
It sounds dramatic and it mostly is. The rehearsal involves loading more than 700,000 gallons of cryogenic propellant into the rocket, running through countdown procedures and practicing the final 10 minutes of the launch sequence — twice, with intentional pauses built in.
Engineers will stop the clock at T-minus 1 minute and 30 seconds, then again at T-minus 33 seconds, resetting back to T-minus 10 minutes each time to run through again. The pauses are designed to let mission managers practice responding to the kinds of problems — technical issues, weather holds, system anomalies — that can appear in the final stretch of a countdown when automated systems take over control of the rocket. A simulated launch time of 8:30 p.m. ET is the target. Nobody is actually going anywhere Thursday, but everything will run as if they are.
What NASA is watching most closely
The repairs made after the Feb. 2 leak are the main thing under evaluation. Engineers replaced two seals on fueling lines connected to the rocket’s liquid hydrogen system after identifying the source of the original leak. A subsequent partial fueling test then revealed reduced hydrogen flow into the booster, traced to a clogged filter in the ground support equipment. That filter has since been replaced.
Thursday’s full fueling test will show whether those fixes hold under real conditions. If the data looks clean and mission managers are satisfied with the rocket’s overall readiness, NASA has identified launch opportunities running from March 6 through March 9, with an additional window on March 11.
The crew waiting on the other side of this test
NASA astronauts Reid Wiseman, Christina Koch and Victor Glover, along with Canadian Space Agency astronaut Jeremy Hansen, will not participate in Thursday’s rehearsal — but they are paying close attention to how it goes. If the test is successful and data reviews clear the rocket for flight, the crew could begin a roughly two-week quarantine period in Houston as early as Friday.
Their mission, once it launches, will mark the first time humans have traveled beyond low Earth orbit since the Apollo 17 crew returned in December 1972. The Artemis II crew is expected to travel farther from Earth than any humans previously have, completing a figure-eight loop around the moon over the course of a 10-day journey. It will also be the first crewed flight for both the Space Launch System rocket and the Orion capsule.
Why this rehearsal matters beyond Thursday
Artemis II is not the finish line — it is the setup for one. Just as NASA used lunar flybys during the Apollo era to build confidence before attempting a landing, Artemis II is designed to verify that the rocket and spacecraft can carry people safely before Artemis III attempts to put astronauts on the lunar surface. That landing mission is currently planned for 2028.
The uncrewed Artemis I mission completed a similar trip around the moon in 2022, but that program also experienced hydrogen leaks during its wet dress rehearsal — delays that pushed the launch back six months. NASA has been here before. The difference this time is that four astronauts are in quarantine waiting rooms, and the moon is no longer a hypothetical destination on a very long timeline.
