NASA prepares for “kinder, gentler” SLS tanking test

PARIS — NASA officials say they are ready to try a new approach to fueling the Space Launch System to prevent the return of leaks that cleared up an earlier launch attempt, even though they’re not certain Not sure what is causing that leak.

Preparations are underway for the September 21 tanking test of the SLS at Launch Complex 39B, with liquid hydrogen and liquid oxygen propellants being loaded into the core stage, which is approximately 7 a.m. Eastern. After the core stage and upper stage tanks are filled, controllers will test a “kickstart bleed” of hydrogen into the core stage engines and perform pre-pressurization tests before wrapping up at approximately 3 p.m. Eastern.

The main purpose of the test is to confirm that repairs to the seals in the liquid hydrogen lines in the core stage, as well as other changes to procedures, eliminate a critical leak seen in the second attempt to launch the rocket on the Artemis 1 mission Sept. 3. Controllers observed the concentration of hydrogen in the enclosure surrounding the connection to be at least twice the limit of 4%.

Workers replaced seals for two liquid hydrogen quick-disconnect fittings. The large, 20 centimeters in diameter, foreign object is a “witness mark” or indentation associated with the debris, NASA Artemis mission manager Mike Sarafin said. The size of the indentation was about 0.25 millimeters. “An indentation of that size provides an opportunity for a pressurized gas to leak through,” especially hydrogen, he said.

However, call agency officials later backed down on the hypothesis that foreign object debris caused the indentation, noting that no debris was recovered. They were also hesitant to conclude that the source of the leak was the indentation.

“There are a lot of things that could have created the indentation. We believe that the indentation corresponds to the leak, but we don’t know it completely,” said John Blevins, chief engineer at NASA SLS.

Tom Whitmire, deputy associate administrator for Common Exploration Systems Development at NASA Headquarters, noted that the leak did not appear during the first SLS launch attempt on Aug. He suggested that several factors may have played a role in the leak.

“There’s definitely more than one aspect to this situation that we don’t really fully understand,” he said. “We’ve looked at every possible avenue that could be related to this and are making sure we’ve done everything we can.”

This includes a new “kinder, gentler” loading approach for liquid hydrogen, which uses low pressure to push liquid hydrogen into the core stage. “We are trying to reduce both pressure spikes and thermal spikes,” said Jeremy Parsons, deputy manager of the Exploration Ground Systems Program. “The team thinks this helps mitigate some of the risks.”

Agency officials said they should know very quickly after testing whether the new seals and refueling process were successful in preventing a recurrence of the leak. The September 27 launch attempt, however, simply won’t be enough to clear the way for the next available opportunity. NASA is still working with the US Space Force, which operates the Eastern Range, to obtain a waiver for the SLS Flight Termination System (FTS). Authentication of that system expired after the last SLS launch attempt.

“Right now, we are still in the process of having technical discussions with Range. It has been very productive and collaborative. We just need to see where those discussions take us,” Whitmeyer said.

A decision on the FTS waiver is not expected until after the tanking test, Jim Free, NASA’s associate administrator for Exploration Systems Development, said in a Sept. 18 presentation at the International Astronaut Congress here.

The approval of the FTS waiver, and launch on September 27, could come over the wire. A mission management team meeting is scheduled for September 25, Sarafin said, “the formal decision door where we will decide whether or not we want to pursue that particular effort.”

He said that the decision could come soon. “It depends on what Wednesday’s outcome is and what, if anything, we need to change or learn from between now and then.”

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