SLS on pad
After a second scrubbed countdown test April 4, NASA will wait until after a crewed SpaceX launch April 8 before trying again. Credit: NASA/Joel Kowsky

Updated 10 p.m. Eastern after NASA decision to roll back SLS.

WASHINGTON — NASA announced late April 16 it will roll back the Space Launch System from the launch pad for various repairs, further delaying the rocket’s long-anticipated first launch.

In a statement late April 16, NASA announced it planned to roll back the SLS to the Vehicle Assembly Building (VAB) “due to upgrades required at an off-site supplier of gaseous nitrogen used for the test,” the agency said. Problems with the supply of gaseous nitrogen, used to support activities at the pad, had delayed two previous countdown rehearsals.

NASA did not state when the vehicle would go back from Launch Complex 39B, where it rolled out March 17, to the VAB. The agency said it will hold a briefing April 18 about its plans. The agency added it would use the time in the VAB to repair a faulty helium check valve in the SLS’s upper stage and a hydrogen leak detected shortly after starting to load liquid hydrogen into the rocket’s core stage during the April 14 attempt. It was the first time that controllers had reached that stage of the countdown after technical problems halted two previous attempts before liquid hydrogen could start loading.

The leak is on the ground side of an umbilical plate on the mobile launcher’s tail service mast, and not on the SLS itself. “The good news is that there’s only a few things in that purge enclosure and there’s a couple of discrete penetrations that could be the culprit,” said Charlie Blackwell-Thompson, Artemis launch director, during an April 15 briefing.

At that briefing, agency officials expressed some optimism about correcting the problem on the pad. Mike Sarafin, NASA Artemis mission manager, said those potential sources for the leak represented “low-hanging fruit” for fixing the problem and allowing another wet dress rehearsal as soon as April 21.

However, he suggested even then that rolling the SLS back the VAB was an option. “There are some more invasive options that require getting further into the hardware and potentially having to get into some extended troubleshooting,” he said, work he indicated might be best done in the VAB.

Sarafin said engineers also had to consider environmental issues of having the vehicle on the pad for an extended period, such as wind stresses on the towering vehicle. “The longer we stay at the pad, the more we stress the vehicle,” he explained. “Every time the wind blows against it, it creates a bending moment and, over time, that adds up.”

“We haven’t fully outlined all the options right now,” he said at the April 15 briefing. “The one that we’re pursuing with great vigor is the low-hanging fruit option and we’ll let the team come up with some other options.”

Blackwell-Thompson suggested one option would be to do another tanking test once the vehicle returns to the pad for the Artemis 1 launch. “You could certainly look at your schedule risk for launch countdown and make a decision whether or not you wanted to do a tanking prior to a launch countdown,” she said. In that scenario, the rocket would go through a tanking test and practice countdown and, if all went well, “some days later decide to go launch.”

Despite not getting through the countdown test in three attempts to date, and uncertainty about when the hydrogen leak will be fixed, Blackwell-Thompson said she was not particularly concerned. She noted there were five or six tanking tests before the first launch of the shuttle more than four decades ago. “Putting it into context, I would say we’re within family of our experience in the past for first-time ops,” she said.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...