This past weekend, April 3, NASA’s Exploration Ground Systems (EGS) office was supposed to conduct the Wet Dress Rehearsal for the Artemis 1 Space Launch System rocket. This would have been a complete countdown test doing all of the same procedures as a real launch, going right up to the moment of engine ignition ten seconds before launch. We were all excited to share this milestone with you, but instead, you get a lesson in how developing and testing a new rocket isn’t easy.

After rollout two weeks ago on March 18, engineers got the rocket hooked up to the pad systems and began to turn it on. The Wet Dress Rehearsal was scheduled to end on April 3, with the countdown actually starting 45 hours before that. Everything went smoothly, even as a lightning strike near the pad hit one of the lightning towers as intended, and not the rocket or its Mobile Launcher. 

That is, until about T-9 hours when it came time to start filling the different stages with their very cold liquid oxygen and liquid hydrogen propellants. However, this first attempt to load propellants was scrubbed because fans that keep toxic gases out of the mobile launcher were not functioning, so technicians could not do their jobs safely. The launch team reset for the next day, yesterday, April 4.

This time, both the weather and the mobile launcher cooperated, and EGS started loading propellant into the SLS rocket — first, liquid oxygen into the core stage. Loading stopped for several hours because of a temperature limit, but after analysis, teams resumed. Then another issue came up, this time with the gaseous hydrogen vent valve on the core stage, specifically the ground system that controls it. This valve directs boiled off hydrogen out of the core stage so that it does not rupture. The team didn’t have time to solve this issue before their shift ended, so the launch director called another scrub.

What does this tell us? That rockets aren’t easy. They are massive, immensely complicated machines that even if they’ve worked once or a few times, that’s not a guarantee they will continue to work, especially if there are new systems involved that worked separately. EGS will try again in a few days and will eventually get the Wet Dress Rehearsal done, and we’ll be here to tell you all about it.

More Information

Artemis I Wet Dress Rehearsal Preparations Underway (NASA)

Artemis I Wet Dress Rehearsal Called off for April 4 (NASA)

NASA Prepares for Next Artemis I Wet Dress Rehearsal Attempt (NASA)