SLS and umbilicals
NASA will replace on the pad a seal for a quick disconnect fitting between a liquid hydrogen fuel line and the core stage of the SLS, keeping open the option for a launch attempt later this month. Credit: NASA/Bill Ingalls

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

In a statement late Sept. 6, NASA said that technicians will proceed with plans to replace the seal for the interface called the quick disconnect between a liquid hydrogen feed line and the core stage of the SLS. That work will be done on the pad rather than rolling the vehicle back to the Vehicle Assembly Building (VAB) at the Kennedy Space Center.

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

At a briefing after the Sept. 3 scrub, NASA officials said that they were considering options to repair the quick disconnect seal while remaining at Launch Complex 39B versus rolling back to the VAB. Staying at the pad has “a couple of pros and cons associated with it,” said Mike Sarafin, Artemis mission manager. “The cons happen pretty much every afternoon around here when you get a shower or thunderstorm coming through.”

NASA said in its latest statement that, before starting work replacing the seal, technicians would place an enclosure around the interface “to protect the hardware from the weather and other environmental conditions.” The agency did not state how long either that preparatory work, or the replacement of the seal itself, would take.

One advantage of doing the work at the pad is that workers can then test the fitting using liquid hydrogen there, which is not an option if the work is done back at the VAB. “That is the only place we can get a full cryo test and be sure we do not have a further issue with respect to leaks at the temperatures we need to fill the vehicle on the day of launch,” Sarafin said.

Doing the work on the pad would also preserve the option of proceeding with another launch attempt without rolling back to the VAB. That is only possible, though, if the U.S. Space Force’s Space Launch Delta 45, which operates the Eastern Range, extends the certification of the flight termination system (FTS) on the rocket. That certification expired Sept. 6, and NASA would have to roll back to the VAB to reset the FTS, which is in a part of the rocket that can’t be accessed on the pad.

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

If, however, the Eastern Range does extend the FTS certification, it could be possible to attempt another SLS launch during the next launch period, which opens Sept. 20 and runs through Oct. 4. “I think it’s too early to tell” if a late September launch is feasible, Sarafin said. “It really comes down to what the fault tree analysis tells us and what are the necessary changes and mitigations required in order have the confidence that we’ve resolved this.”

Free said other factors could weigh into a decision to remain on the pad, including any constraints for the Orion spacecraft remaining at the pad. “Ultimately we’re driven by the FTS.”

If NASA decides to roll back to the VAB, which could be to perform other work on the vehicle or because of weather as Florida enters the peak of the hurricane season, it would delay the launch by several weeks, Sarafin said. That would push the launch back to at least the next launch period, which runs from Oct. 17 through 31.

The Sept. 6 update from NASA did not provide additional details on what caused the quick disconnect seal to leak. Agency officials speculated after the scrub that an “inadvertent overpressurization” of the liquid hydrogen line during preparations for fueling could have damaged the seal, but said they needed more time to investigate the issue.

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...