Contamination found in SLS engine tubing

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Updated 4 p.m. Eastern May 18 with comment from NASA.

WASHINGTON — NASA is dealing with a contamination problem with tubing in part of the core stage of the first Space Launch System vehicle, an issue that could contribute to further delays for its launch.

At a May 17 meeting of the Aerospace Safety Advisory Panel (ASAP) at NASA’s Kennedy Space Center, panel member Don McErlean said the committee had been briefed on a “late development” with the core stage, being constructed at the Michoud Assembly Facility in New Orleans.

A “routine quality assurance inspection” of the core stage, he said, discovered contamination in tubing in the engine section of the core stage, which hosts the vehicle’s four RS-25 main engines and associated systems. That contamination turned out to be paraffin wax, which is used to keep the tubes from crimping while being manufactured but is supposed to be cleaned out before shipment.

“The prime contractor determined the vendor was not fully cleaning the tubes and it was leaving residue in the tubes,” McErlean said. “This was retained as a requirement in the prime contractor’s spec, but it was not properly carried out.” Boeing is the prime contractor for the SLS core stage, but he did not disclose the vendor who provided the contaminated tubing.

The contamination was initially found in a single tube, he said, but later checks found similar residue in other tubes. All the tubing in the core stage is now being inspected and cleaned, a process he said is not straightforward because of the “mass of tubing” in the engine section and also because cleaning is a “non-trivial process.”

Janet Anderson, a spokesperson at NASA’s Marshall Space Flight Center, said May 18 that the contamination was discovered while working a tube installation in the engine section in February. “All core stage tubes have been reviewed by engineering for action or use as is,” she said. “The tubes that have been determined to need further action are all in the process of being re-cleaned and inspected.”

Besides cleaning the contaminated tubing, the program is instituting new inspections and other changes to its quality assurance plans. ASAP, McErlean said, had no specific recommendations for dealing with the problem, finding that the program had already instituted any corrective actions it would have recommended.

McErlean didn’t state if the tubing problem would affect the schedule for the completion of the core stage. NASA had previously said they expected the core stage to be completed and shipped to the Stennis Space Center in Mississippi at the end of this year for so-called “green run” engine tests by mid-2019, after which it would go to the Kennedy Space Center to be prepared for launch on Exploration Mission (EM) 1.

In a March 26 presentation to the NASA Advisory Council’s human exploration and operations committee, Bill Hill, deputy associate administrator for exploration systems development, briefly mentioned “contamination in our tubes” in the SLS core stage engine section but didn’t go into details and downplayed the problem. “We believe we’ve turned the corner on that and understand it and have those tubes cleaned,” he said.

Hill said that, at the time, the engine section of the SLS core stage was set to be completed in May, but that it could slip to August. “That’s a couple month’s risk, and we’ll see how that works out,” he said.

Hill’s charts also showed three to four months of schedule risk for completion of the core stage, still scheduled for December 2018, and the same amount of schedule risk for the June 2019 delivery of the core stage to the Kennedy Space Center.

Anderson said NASA is working with Boeing to determine the schedule effect the problem will have on the overall SLS program. “NASA is reviewing the impact of this decontamination effort on the Core Stage schedule, including delivery to the Stennis Space Center for green run testing and delivery to the Kennedy Space Center for EM-1 launch preparations.”

That schedule from March continued to call for launch of EM-1 in the latter half of December 2019, but again with several months of schedule risk. “We feel that it’s the appropriate thing to do at this point,” Hill said of maintaining the December 2019 date. “We have a lot of mitigation activities in work across the board.”