NASA braces for ‘friendlier, gentler’ SLS tank test – SpaceNews

PARIS — NASA officials say they’re ready to try a new approach to refueling the space launch system to prevent the return of leaks that eliminated a previous launch attempt, though they’re not sure what caused that leak.

Preparations are underway for the September 21 refueling test of the SLS at Launch Complex 39B, with loading of liquid hydrogen and liquid oxygen propellants into the core stage beginning at approximately 7 a.m. After filling the core and upper stage tanks, controllers conduct tests of a “kickstart bleed” of hydrogen into the core stage engines and a pre-pressurization test before concluding at approximately 3:00 p.m. EST.

The primary objective of the test is to confirm that repairs to seals in liquid hydrogen lines into the core stage, as well as other procedural changes, will eliminate a significant leak observed during the rocket’s second launch attempt on the Artemis-1 mission in September. 3. Inspectors saw hydrogen concentrations in the enclosure around the compound at least twice a 4% limit.

Workers replaced the seals for two liquid hydrogen quick connectors. The larger, 20 centimeters in diameter, has a “witness mark” or indentation associated with foreign object debris, said Mike Sarafin, NASA Artemis mission manager. The size of the indentation was approximately 0.25 millimeters. “A depression of this size presents the opportunity for a pressurized gas to pass through,” he said, specifically hydrogen.

However, later in the conversation, agency officials backed down from the hypothesis that the debris caused the indentation, noting that no debris was recovered. They were even reluctant to conclude that the depression was the source of the leak.

“There are just so many things that could have caused the indentation. We think the indentation coincides with the leak, but we don’t know that for sure either,” said John Blevins, NASA SLS chief engineer.

Tom Whitmeyer, deputy associate administrator for joint exploration systems development at NASA Headquarters, noted that the leak did not occur during the first SLS launch attempt on Aug. 29. He suggested several factors may have played a role in the leak.

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

These include a new “friendlier, gentler” liquid hydrogen charging approach, in which liquid hydrogen is pushed through the lines and into the core stage at less pressure. “We’re trying to minimize both pressure spikes and thermal spikes,” said Jeremy Parsons, associate manager of the Exploration Ground Systems program. “The team believes this helps mitigate some of the risks.”

Agency officials said they should know fairly quickly after the test whether the new seals and refueling process were successful to prevent the leak from reoccurring. However, that alone will not be enough to clear the way for a September 27 launch attempt, the next available opportunity. NASA is still working with the US Space Force, which operates the Eastern Range, to obtain an exemption for the SLS Flight Termination System (FTS). This system’s certification expired after the last SLS start attempt.

“At the moment we are still in the process of having technical discussions with the range. It was very productive and collaborative. We’ll just have to see where these discussions take us,” Whitmeyer said.

A decision on an FTS waiver is not expected until after the tank test, said Jim Free, NASA assistant administrator for exploration systems development, in a presentation Sept. 18 at the International Astronautical Congress here.

Approving the FTS waiver and a September 27 launch could be on the table. A mission management team meeting is scheduled for September 25, Sarafin said, a “formal decision point at which we will decide whether we want to proceed with this particular attempt.”

A decision could be made sooner, he added. “It depends on what the outcome is from Wednesday and what, if anything, we need to change or learn by then.”