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

COLORADO SPRINGS — After a series of problems scrubbed a second countdown rehearsal for the Space Launch System April 4, NASA will wait until after the launch of a SpaceX mission to the space station before trying again.

NASA halted the wet dress rehearsal (WDR) for the SLS at Launch Complex 39B at about 5 p.m. Eastern April 4. The decision to stop the test came after controllers could not open a vent valve on the mobile launcher required to start loading of liquid hydrogen into the rocket’s core stage. Technicians later found that the valves were physically closed in a way such that they could not be remotely commanded to open.

NASA was several hours behind schedule that day because of other problems earlier in the test. An interruption in the supply of nitrogen gas at the launch site delayed the start of test activities early in the day. Shortly after liquid oxygen started going into the core stage, a temperature limit warning stopped fueling for several hours while engineers reconfigured the propellant loading process.

At an April 5 briefing, NASA officials said that they made progress through some of the milestones of the overall WDR process, including filling the core stage liquid oxygen tank to about 50%. They made more progress than the first attempt April 3, which NASA scrubbed before any propellants could be loaded into the vehicle. “A significant amount of our objectives have been completed,” said Charlie Blackwell-Thompson, NASA Artemis launch director.

NASA has not announced when they’ll try again, but it won’t be before the Falcon 9 launch of the commercial Ax-1 mission for Axiom Space to the International Space Station from neighboring Launch Complex 39A, scheduled for April 8.

“We will follow Axiom on the range,” said Jim Free, NASA associate administrator for exploration systems development, during a panel at the 37th Space Symposium April 5. That mission needs to launch soon to avoid delaying NASA’s Crew-4 crew rotation mission to the ISS, also launched by SpaceX from LC-39A, now scheduled for April 20.

NASA officials said they also needed the time to get ready for another countdown attempt. “We’ve got to finish sharpening the pencil on the open work, but we don’t anticipate it will be too much longer than after the Axiom launch,” said Mike Sarafin, NASA Artemis mission manager, at the briefing.

NASA doesn’t consider any of the problems encountered so far in the two countdown rehearsal attempts to be serious issues with the SLS or ground systems. “It’s working through a lot of issues of bringing the vehicle together for the first time,” said Free.

“We haven’t run into any fundamental design flaws or design issues. These are what I would characterize as nuisance or technical issues where we’re learning features and systems that we characterized in subscale testing, but when you put it all together you learn where some of your uncertainties are,” said Sarafin.

Those problems will affect the schedule for the Artemis 1 mission, which had been looking to launch as soon as a window that runs from June 6 to 16. “We’re not ready to give up on it yet,” he said of that launch window. “We’ll reassess after wet dress.”

By then NASA hopes to resolve another nuisance: a lack of detailed commentary during the countdown rehearsals, which the agency blamed on export control restrictions on technical information. NASA instead provided intermittent updates through social media and blogs.

“We are working on having launch commentary. I know that’s been something that folks really want,” Free said. “We’re working towards that for launch.”

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...