SLS and umbilicals

NASA prepares for ‘kinder, gentler’ SLS tanking test – SpaceNews

PARIS – NASA officials say they are ready to try a new approach to powering the space launch system to prevent the return of leaks that wiped out an earlier launch attempt, even if they are not certain of the cause. of this leak.

Preparations are underway for the Sept. 21 tank test of the SLS at Launch Complex 39B, with loading of liquid hydrogen and liquid oxygen propellants into the core stage beginning around 7 a.m. ET. ‘East. After filling the mid-stage and upper-stage tanks, the controllers will perform hydrogen “start-purge” tests in the mid-stage engines and a pre-pressurization test before concluding towards 3 p.m. Eastern Time.

The primary purpose of the test is to confirm that repairs to the liquid hydrogen line seals in the core stage, along with other procedural changes, eliminate a large leak observed during the rocket’s second launch attempt. during the Artemis 1 mission on September 1. 3. Inspectors have seen hydrogen concentrations in the enclosure around the connection at least twice a 4% limit.

Workers replaced the seals of two liquid hydrogen quick-disconnect fittings. The largest, 20 centimeters in diameter, has a “witness mark” or indentation associated with foreign object debris, said Mike Sarafin, NASA’s Artemis mission manager. The size of the indentation was approximately 0.25 millimeters. “A footprint of this size provides the opportunity for pressurized gas to leak out,” particularly hydrogen, he said.

However, later in the call, agency officials backed away from the hypothesis that foreign object debris had caused the indentation, noting that no debris had been recovered. They were even hesitant to conclude that the indentation was the source of the leak.

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

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

“There’s definitely more than one aspect of this condition that we don’t really understand,” he said. “We looked at all the possible paths that could be linked to it and made sure we did everything we could.”

This includes a new “softer, smoother” charging approach for liquid hydrogen, using less pressure to push liquid hydrogen through the lines to the center stage. “We’re trying to minimize both pressure spikes and thermal spikes,” said Jeremy Parsons, Exploration Ground Systems deputy program manager. “The team feels this helps mitigate some of the risk.”

Agency officials said they should know fairly soon after the test whether the new seals and the refueling process were successful in preventing a recurrence of the leak. However, that alone won’t be enough to pave the way for a launch attempt on September 27, 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). The certification for this system expired after the last attempt to launch SLS.

“At the moment we are still having technical discussions with the range. It has been very productive and collaborative. We just need to see where these discussions take us,” Whitmeyer said.

A decision on an FTS waiver is not expected until after the tanking test, Jim Free, NASA’s associate administrator for exploration systems development, said during a Sept. 18 presentation at the International Space Congress. astronautics here.

Approval of the FTS waiver and a Sept. 27 launch could come down to the wire. A mission management team meeting is scheduled for Sept. 25, Sarafin said, a “formal decision gate where we will decide if we want to proceed with this particular attempt.”

A decision could come sooner, he added. “It depends on Wednesday’s result and what, if anything, we need to change or learn by then.”

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