The Artemis I wet dress rehearsal ended on 20 June at 23:37 CEST at T-29 seconds in the countdown. The test marked the first time the NASA team fully loaded all the Space Launch System rocket’s propellant tanks and proceeded into the terminal launch countdown, when many critical activities occur in rapid succession.

Artemis I SLS with Full Moon
A full Moon at Launch Complex 39B at NASA’s Kennedy Space Center in Florida, USA on June 14, 2022. Credits: NASA

During propellant loading operations earlier in the day, launch controllers encountered a hydrogen leak in the quick disconnect that attaches an umbilical from the tail service mast on the mobile launcher to the rocket’s core stage. The team attempted to fix the leak by warming the quick disconnect and then chilling it back down to realign a seal, but their efforts did not fix the issue.

Launch controllers then developed a plan to mask data associated with the leak that would trigger a hold by the ground launch sequencer, or launch computer, in a real launch day scenario, to allow them to get as far into the countdown as possible. The time required to develop the plan required extended hold time during the countdown activities, but they were able to resume with the final 10 minutes of the countdown, called terminal count. During the terminal count, the teams performed several critical operations  that must be accomplished for launch including switching control from the ground launch sequencer to the automated launch sequencer controlled by the rocket’s flight software, and important step that the team wanted to accomplish.

You can see a live feed of the rocket at launch pad below: