During the lead-up to NASA’s Artemis 1 mission in 2022, repeated hydrogen leaks led to significant delays and a the launch attempt was cancelled. The agency has had three years to address the underlying hardware issues with the Space Launch System (SLS), and yet, Artemis 2’s wetsuit rehearsal feels all too familiar.

NASA engineers noticed a hydrogen leak in one of the mobile launcher’s tail service mast umbilicals during a fueling test, prompting them to finish at the T-5:15 minute mark. These 35-foot-tall (11-meter-tall) structures provide cryogenic propellant lines and electrical cable connections to the SLS core stage. One of them was also the source of the hydrogen leaks that overcame Artemis 1.

In an update on Sunday, the agency SAYS Technicians have replaced two seals inside the tail service mast to address what they believe is the source of the leak, but the real question is, why is this still happening? NASA had three years to fix this issue, and yet, here it is again.

Still working out the kinks

In NASA’s defense, liquid hydrogen is a notoriously difficult fuel to work with. As the smallest molecule—consisting of two bonded hydrogen atoms—it can escape through tiny gaps in seals and joints. The extremely cold temperature of the fuel, which is -423 degrees Fahrenheit (-253 degrees Celsius), can also cause these hardware elements to become brittle and crack.

At the same time, liquid hydrogen offers unmatched energy-to-weight efficiency, meaning it produces more thrust per pound than any other fuel. NASA has been counting on it since the days of the Space Shuttle, and it has worked dealing with leaks since then too.

The SLS was modeled after the Shuttle, so it’s no surprise that this rocket would experience the same problem. It is also important to note that Artemis 1 was the first and only launch to date. Fewer launches mean fewer opportunities to work out kinks, so even though NASA has had three years to address the issues that came up during Artemis 1, the SLS program is still in its infancy.

From that perspective, the Artemis 2 wet dress rehearsal was a great success. It is certainly much smoother than the first attempt to fuel Artemis 1, which is scratched before tanking started due to a pressure issue with the mobile launcher. This time, the engineers did it perfectly load on the top and core stage of the rocket in the first test.

“We really learned a lot from the Artemis 1 mission, and we implemented many of the lessons learned yesterday through the wetsuit,” Lori Glaze, NASA’s Exploration Systems Development Mission Directorate acting associate administrator, said. SAYS during the post-wet dress rehearsal press conference on February 3.

A smooth path forward for Artemis 2?

After NASA scrubbed the first wetsuit rehearsal for Artemis 1, it took four more attempts—followed by three launch attempts—to get the mission off the ground. The agency is now doing everything it can to avoid the same planned timeline for Artemis 2.

In a statement on Sunday, NASA said that engineers are analyzing the removed seals to determine the cause of the leak while reconnecting the interfaces-the plates and quick disconnect connections between the rocket and the mobile launcher that carry fuel lines and electrical cables. The teams will conduct tests to evaluate their recovery before the next wet dress rehearsal.

If NASA can get a handle on hydrogen leaks, Artemis 2 can launch on March 6. As the rocket’s first crewed flight, this mission is a critical test for the agency’s SLS program. We will soon find out if the lessons learned from Artemis 1 have really come to fruition.