SLS and umbilicals

SLS liquid hydrogen leak on NASA repair pad

WASHINGTON — NASA will attempt to repair the liquid hydrogen seal on the launch pad that caused the Space Launch System to scrub, and retains the option to proceed with a new launch attempt later this month.

In a late Sept. 6 statement, NASA said technicians will continue to plan to replace the seal at the interface, known as the quick-disconnect interface between the liquid hydrogen feed tube and the SLS core stage. Instead of rolling the vehicle back to the Kennedy Space Center’s Vehicle Assembly Building (VAB), the work will be done on the mat.

A problem with that seal resulted in what officials called a massive leak of liquid hydrogen during core-stage refueling during the Sept. 3 launch attempt. Several efforts to reinstall the quick-disconnect by heating and then cooling it and applying helium pressure to the fitting failed to stop the leak, and NASA called off a launch attempt for Artemis 1 three hours before the two-hour launch window opened. .

During a post-scrubbing briefing on Sept. 3, NASA officials said they were considering the option of repairing the quick-disconnect seals while remaining at Launch Site 39B, rather than returning to the VAB. Artemis mission manager Mike Sarafin said there were “several advantages and disadvantages” to staying on the mat. “It happens almost every afternoon when you have showers or thunderstorms.”

In its latest statement, NASA said that before starting to replace the seals, technicians will place an enclosure around the interface “to protect the hardware from weather and other environmental conditions.” The agency did not describe preparation or replacement. How long does the seal itself take.

One of the benefits of working on the pad is that workers can use the liquid hydrogen test fittings there, which is not an option if the work goes back to the VAB to be done. “This is the only place where we can do a full cryogenic test and make sure we don’t have further leak issues at the temperatures needed to fill the vehicle on launch day,” Sarafin said.

Doing this on the launchpad will also preserve the option to proceed with another launch attempt without rolling back to the VAB. However, this is only possible with the certification of the US Space Force’s Space Launch Delta 45 Extended Rocket Flight Termination System (FTS), which operates the Eastern Range. The certification expires on September 6, and NASA will have to roll back to the VAB to reset the FTS, which is part of the rocket and cannot be accessed from the launch pad.

“We don’t have an FTS waiver beyond 25 days right now. Before we can do that, we have to roll back,” Jim Free, NASA’s associate administrator for exploration systems development, said at a Sept. 3 briefing. He said the agency would consider seeking an extension but would need to determine how long it would take and how much the Eastern Sierra would grant. “That negotiation hasn’t happened yet, so as far as I’m concerned, we have to roll back.”

However, if Eastern Range does extend its FTS certification, it is possible to attempt another SLS launch during the next launch period, which begins on September 20 and runs through October 4. “I think it’s too early to tell if it’s too early,” Sarafin said, saying a launch in late September is feasible. “It really comes down to what the fault tree analysis tells us, and what necessary changes and mitigations need to be made to be confident that we’ve fixed the problem.”

Other factors could influence the decision to stay on the pad, Free said, including any restrictions on Orion spacecraft remaining on the pad. “Eventually we were driven by FTS.”

If NASA decides to go back to the VAB, it could be to perform other work on the vehicle, or it will delay the launch by several weeks due to weather in Florida heading into the height of hurricane season, Sarafin said. This will delay the launch until at least the next launch period, which runs from October 17 to 31.

NASA’s September 6 update did not provide more details about the leak that caused the quick-disconnect seal. Agency officials speculated after the scrub that “unintentional overpressure” in the liquid hydrogen lines during preparation for refueling could have damaged the seals, but said they needed more time to investigate the issue.

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