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NASA is keeping open the option of attempting another launch of the SLS on the Artemis 1 mission as soon as Sept. 2 as engineers study two problems that scrubbed the first launch attempt. Credit: Jordan Sirokie

KENNEDY SPACE CENTER, Fla. — NASA officials say they are keeping open the possibility of attempting another launch of the Artemis 1 mission as soon as Sept. 2 as they continue to study a pair of issues that scrubbed the initial launch attempt Aug. 29.

At a briefing several hours after the scrub, agency leaders said they were still examining the root cause of the postponed launch and were not prepared to either set a new launch date for the inaugural Space Launch System flight or conclude that the rocket should be rolled back to the Vehicle Assembly Building (VAB) for repairs.

“Friday is definitely in play” for a launch attempt, said Mike Sarafin, Artemis 1 mission manager. Sept. 2 is the next possible launch date because of constraints on Orion’s trajectory to the moon to avoid extended eclipses that deprive the spacecraft of power. “We’re preserving the option for Friday.”

Controllers scrubbed the launch when they were unable to resolve a hydrogen bleed line issue with one of four RS-25 engines in the core stage. The bleed is designed to flow hydrogen into the engines to condition them thermally for flight. For three of the engines, the bleed was working as planned, cooling the engines to the required temperature, but for the fourth, designated engine #3, it did not cool down sufficiently.

Efforts to get hydrogen flowing into the engine by increasing pressure in the system were complicated by a separate problem with a vent valve in the intertank portion of the core stage between the liquid hydrogen and liquid oxygen tanks. Sarafin said engineers are still studying the valve problem but it appeared to involve a leak.

“The challenge that created was we wanted to increase the pressure in the tank in order to establish the hydrogen bleed, and the vent valve wasn’t cooperating,” he said. “That was the point where the team decided that it was appropriate to declare the scrub because we just weren’t going to make the two-hour window. It was one of those situations where we just knew we needed more time.”

While the cause of the bleed problem in engine #3 remains under investigation, Sarafin said he believed the issue was not with the engine itself, something that might require replacing it back in the VAB. “It’s in the bleed system that thermally conditions the engines,” he said, located in the core stage.

That bleed system was not tested in the most recent wet dress rehearsal of the SLS in June because of a leak in a quick-disconnect fitting in a hydrogen line. NASA decided to go ahead with a launch attempt despite not getting through the full countdown rehearsal, moving up the bleed test earlier in the countdown. “If we do not successfully demonstrate that, we are not going to launch that day,” Sarafin said at an Aug. 22 briefing.

Jim Free, NASA associate administrator for exploration systems development, defended NASA’s decision to proceed with a launch attempt rather than first do another rehearsal to confirm the hydrogen bleed was working. “We would have taken another cycle of rolling out and back,” he said at the briefing, which introduces risk, while not accomplishing tasks like closing out the Orion spacecraft for launch and setting up the rocket’s flight termination system.

“We won’t know until we know, but we also won’t know until we try,” he said. “We felt like we were in the best position to try.”

Even without the technical issues, it may have been difficult to launch Artemis 1 in the two-hour window that was available on the morning of Aug. 29. Weather conditions were no-go at the start of the window because of precipitation and no-go again later in the window because of lightning, Sarafin said.

Weather could also be an issue if NASA goes ahead with a Sept. 2 launch. A forecast issued after the scrub Aug. 29 by Space Launch Delta 45 predicted only a 40% chance for acceptable weather during a two-hour window that opens at 12:48 p.m. Eastern because of the potential for storms. There are additional launch opportunities through Sept. 6, after which the next window opens Sept. 20.

Sarafin said NASA would be able to provide more details, including the prospects for a launch Sept. 2 or later, after a mission management meeting scheduled for the afternoon of Aug. 30. He added after the briefing that could include deciding to proceed with a Sept. 2 launch “at risk” by starting a countdown nearly 48 hours earlier while still attempting to resolve the issues with the bleed line and vent valve.

“We really need more time to look at all the information, all the data,” he said. “We’re going to play all nine innings here. We’re not ready to give up yet.”

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...