Teams at Kennedy Space Center conducted and mostly completed a critical Wet Dress Rehearsal for the launch of the Artemis II rocket and ground support teams yesterday. The test was not without problems: Hydrogen leaks at the tail mast area of the pad and an issue closing Orion’s hatches bedeviled the tests, resulting in NASA announcing that the launch of the Artemis II mission is now no earlier than March 6, 2026.

“The Artemis II wet dress rehearsal countdown was terminated at the T-5:15 minute mark due to a liquid hydrogen leak at the interface of the tail service mast umbilical, which had experienced high concentrations of liquid hydrogen earlier in the countdown, as well,” NASA said.

In a press conference today, Artemis II Launch Director Charlie Blackwell-Thompson said, “When we got into the LH₂ fast fill—which was around 12:29—is when we picked up our first leak in the SMU, in the cavity, which is where the flight and the ground plate come together. It’s that cavity in between. It’s in our eight-inch fill and drain line there. We have a QD that connects those two together.”

“It was similar to some of the signatures we saw during Artemis I. Our leak rate was a little bit higher—somewhere around 12 to 14%,” Blackwell-Thompson continued. “We tried a contingency procedure that we used during Artemis I: you let that QD warm up, you let the seal warm up, and you try it again. We did that a couple of times, worked our way through it, and were able to load the core stage all the way to replenish.”

When asked what items were missed in the Wet Dress Rehearsal, Blackwell-Thompson said, “What we didn’t get to do: we wanted to get through terminal count. We wanted to get inside terminal count, hold, and verify our three-minute hold capability—tanks in launch-ready state and you can hold them for up to three minutes.”

“We also wanted to demonstrate a recycle: come down, have a planned cutoff, come back and retarget a new T-0 within the launch window. Didn’t get a chance to do that.”

What’s Next

Before the March window, NASA’s engineers and mission managers will review data, equipment and procedures from the WDR yesterday and they will conduct a second Wet Dress Rehearsal before committing to a launch date. Of key interest are the Tail Mast interfaces that deliver LH₂ to the rocket’s propellant tanks.

“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,” NASA Administrator Jared Isaacman said today. “With more than three years between SLS launches, we fully anticipated encountering challenges. 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.”

Remaining Launch Windows

The Good and The Bad

A liquid hydrogen leak at the LC-39B’s Tail Mast umbilical connection to SLS’s core stage forced engineers into a troubleshooting effort that pushed the countdown about two hours behind schedule. The team cycled through several repair attempts, first halting LH₂ flow, then letting the interface warm so seals could seat themselves properly, and finally by tweaking propellant flow rates before pressing ahead. Ultimately, they were successful in their efforts and got the 322-foot tall rocket fully fueled, but a great deal of time was lost during the effort.

Secondly, a recently replaced valve tied to Orion’s crew hatch pressurization system needed to be retorqued, and closeout work ran longer than expected. NASA stated around 10 PM last night that, “The closeout crew remains in the White Room and has closed the Orion spacecraft’s crew module hatch. While performing seal pressurization checks on the counterbalance assembly, which could be used to help open the hatch, a valve associated with Orion’s hatch pressurization was inadvertently vented. The counterbalance assembly then needed to be repressurized to allow work to continue.”

Finally, communications issues from SLS to ground caused some issues and will need to be remediated prior to the next Wet Dress Rehearsal, much less any launch attempt in March.

Clearly, there’s some work to do before Artemis II will be ready to fly.

The Artemis II crew has been released from quarantine for the time being. Once a new potential launch date becomes clearer, they will return to quarantine and fly to Kennedy Space Center for final preparations prior to launch.

NASA has scheduled a 1 PM ET press conference to offer more details.