The fourth attempt of a final prelaunch test started on Saturday and the rocket tanks were filled on Monday.
The crucial test, known as the wet dress rehearsal, simulates every stage of launch without the rocket leaving the launchpad at Kennedy Space Center in Florida.
This process includes loading supercold propellant, going through a full countdown simulating launch, resetting the countdown clock and draining the rocket tanks.
The results of the wet dress rehearsal will determine when the uncrewed Artemis I will launch on a mission that goes beyond the moon and returns to Earth. This mission will kick off NASA’s Artemis program, which is expected to return humans to the moon and land the first woman and first person of color on the lunar surface by 2025.
Three previous attempts at the wet dress rehearsal in April were unsuccessful, concluding before the rocket could be fully loaded with propellant due to various leaks. These have since been corrected, NASA says.
The NASA team rolled the 322-foot-tall (98-meter-tall) Artemis I rocket stack, including the Space Launch System and Orion spacecraft, back to the launchpad at Kennedy Space Center in Florida on June 6.
Wet dress rehearsal steps
The wet dress rehearsal began at 5 p.m. ET Saturday with a “call to stations” — when all of the teams associated with the mission arrive at their consoles and report they’re ready for the test to begin and kick off a two-day countdown.
Preparations over the weekend set up the Artemis team to start loading propellant into the rocket’s core and upper stages Monday morning.
Tanking was on hold Monday morning because of an issue identified with the backup supply of gaseous nitrogen. The launch team replaced the valve causing the issue. In order to make sure the backup supply is functioning as expected, it was swapped in as the primary supply for the test.
The hold lifted at 9:28 a.m. ET. Liquid oxygen, cooled to minus 297 degrees Fahrenheit (minus 182 degrees Celsius), and liquid hydrogen were used to fill the core stage before moving on to the rocket’s upper stage. Venting was visible from the rocket throughout the process.
The core stage was mostly filled and the team was filling the upper stage when several issues occurred just after 2 p.m. ET.
The team discovered a hydrogen leak at a quick disconnect line for the core stage. Their first option did not work and they looked into options to seal the leak.
Something from the flare stack, where excess liquid hydrogen from the rocket is burned off with propane flames, caused a small grass fire burning toward a dirt road. The team monitored the grass fire and expected the fire to die out when it reached the dirt road.
The test exceeded a planned 30-minute hold, which was extended as engineers tried to work on solutions for the hydrogen leak.
The Artemis team decided to go through with one countdown, while masking the hydrogen leak issue, “in order to get further into the testing for today’s wet dress rehearsal,” according to a tweet from NASA’s Exploration Ground Systems.
The 10-minute countdown began at 7:28 p.m. ET.
Typically, there are two countdowns during the wet dress rehearsal. First, team members usually go through a countdown to 33 seconds before launch, then stop the cycle. The clock is reset, and then the countdown resumes again and runs until about nine seconds before a launch would occur.
Monday’s abbreviated countdown ended prematurely with 29 seconds left on the countdown clock. A flag from the SLS rocket’s computer triggered the cutoff, but the exact flag has not been shared. Prior to the countdown, the team said if the computers involved in the countdown sense the hydrogen leak, it might be akin to a check engine light that forces a premature stop to the countdown.
Once the countdown halted, the Artemis team worked on ensuring that the vehicle was safe.
Charlie Blackwell-Thompson, Artemis launch director for NASA’s Exploration Ground Systems Program, said it was “definitely a good day for us” after achieving multiple milestones outlined in the wet dress objectives, like fully tanking the rocket and getting through a countdown.
The next steps will be assessing all of the data collected from the test, including the issues, and laying out a plan to go forward, she said.
The previous wet dress rehearsal attempts have already completed many objectives to prepare the rocket for launch, Blackwell-Thompson said.
There is a long history behind the arduous testing of new systems before a launch, and the Artemis team faces similar experiences to those of the Apollo- and shuttle-era teams, including multiple test attempts and delays.