The agency will host a news conference on Friday to share updates and next steps for the test.
The mission team had been attempting to fuel the 322-foot-tall (98-meter-tall) Artemis I rocket stack, including NASA’s Space Launch System and Orion spacecraft, at Kennedy Space Center in Florida, but encountered a number of delays.
“The team will not conduct the terminal countdown activities today as planned and will assess next steps after today’s operations,” according to a tweet from Jeremy Parsons, deputy manager of the Exploration Ground Systems program at Kennedy Space Center.
The rocket remains stable and in a safe configuration, according to the agency.
The crucial test, known as the wet dress rehearsal, simulates every stage of launch without the rocket actually leaving the launchpad. This includes loading propellant, going through a full countdown simulating launch, resetting the countdown clock and draining the rocket tanks.
The process was previously adjusted in response to an issue encountered over the weekend during preparations for this attempt.
“Any new rocket that comes forward in a new program like this kind of goes through these updates and understanding how the rocket is performing,” said Tom Whitmeyer, deputy associate administrator for exploration systems development at NASA Headquarters, during a news conference Monday. “And that’s the type of thing that we’re going through right now.”
A modified test
The issue engineers identified over the weekend is a malfunctioning helium check valve. Helium is used to purge the engine before loading supercold propellant — the wet in wet dress rehearsal — during fueling. Check valves allow gas or liquid to flow in one direction to prevent backflow. In this case, the part that isn’t working is about 3 inches (7.6 centimeters) long and keeps helium from flowing back out of the rocket.
The valve is difficult to reach while the rocket sits on the launchpad, but it can be replaced or fixed after the run-through is complete. The modified version of the wet dress rehearsal is still necessary, however, to ensure the safety of the rocket’s flight hardware.
The modified test will take the strain off of the valve and the upper rocket stage with minimal propellant operations. Previously, the team had planned to fully fuel the core and upper stages of the rocket, but the valve issue prevents that step from taking place during this test. Assessments will be made to see whether further tests are needed.
The rocket and spacecraft were powered up Wednesday night, and the team conducted a meeting at 6 am ET Thursday to assess the weather and review the status of operations. The team extended a hold, which was expected to last an hour and a half to two hours, after experiencing “an issue with an outage at an off-site vendor of gaseous nitrogen used inside the rocket before propellant loading,” according to an update from NASA officials. This issue is similar to one experienced during a previous attempt on April 4.
The gaseous nitrogen is used to purge oxygen from the rocket prior to fueling, and it’s a safety measure. The team was able to reestablish the supply of gaseous nitrogen and begin fueling after 8 am ET.
Fueling begins with chilling liquid oxygen lines for the core stage of the rocket. Then, liquid oxygen and liquid hydrogen fill the core stage through these lines, getting topped off and replenished as some of the supercold propellant boils off, according to the agency. The team will chill propellant lines for the rocket’s upper stage as well, but not release any propellant due to the existing valve issue.
The Artemis rocket core stage can hold 198,000 gallons (900,126 liters) of liquid oxygen that is cooled to negative 297 degrees Fahrenheit (negative 182 degrees Celsius). A total of 537,000 gallons of propellant will be loaded into the rocket when the core stage is fully fueled.
“Hydrogen is extremely hazardous, cold, and a small molecule that is known for leaking. All of these systems have been sealed, leak checked and tested to the highest extent possible prior to wet dress rehearsal,” according to a tweet from Jeremy Parsons, deputy manager of the Exploration Ground Systems program at Kennedy Space Center.
“Under the unique operating conditions with the rocket we are prepared and know leaks are a realistic possibility. We have amazing hazardous gas and leak detection systems that keep the rocket safe and alert us to conditions outside of normal parameters.”
The team will continue chilling down the hydrogen lines connected to the upper stage of the rocket to collect more data, and there are no plans to load liquid hydrogen or liquid oxygen into the upper stage tanks.
The core stage liquid hydrogen tank was about 5% full, and the liquid oxygen tank was 49% full. The propellant will be drained, and the team will inspect the leak and come up with a plan to move ahead.
Learning valuable lessons
Once this test is complete, the Artemis I rocket will be rolled back into the Vehicle Assembly Building at the space center.
The previous attempts at the wet dress rehearsal have already provided valuable insight, officials said, even as the team has worked through various issues.
While the exact issues identified during the test attempts weren’t anticipated, it’s part of the process when testing out a new rocket.
“I can say that these will probably not be the last challenges we’ll encounter,” said Mike Sarafin, Artemis mission manager at NASA Headquarters, during the conference. “But I’m confident that we have the right team in place and the ability to rally around those problems and overcome them is something that we take pride in.”
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 the first person of color on the lunar surface by 2025.
The current launch window possibilities include June 6 through June 16, June 29 through July 17 and July 26 through August 9, Sarafin said.