Why did Space Launch System’s Green Run hot fire test abruptly end early? NASA can explain …

NASA released a statement this week detailing information about some of the findings that contributed to the early shutdown of the Artemis 1 Core Stage during the Green Run Hot Fire test on Saturday. The test was originally supposed to last about 8 minutes, but ended up only lasting 67.2 seconds, far short of the minimum amount of time needed to certify the core.

While many speculated of major problems that could push the first mission in NASA’s Artemis program to next year, it seems to be possibly only a minor setback for NASA. Initial findings show that the shutdown was caused by parameters that were set extra conservatively for ground testing to ensure the safety of the Core Stage.

The parameters were tripped by one of the Core Stage Auxiliary Power Units (CAPU) that power the hydraulic systems of Engine 2 of the stage. As planned, the computers running the test order the engine to stop firing its engines and halt the test. While this happened on the ground, this wouldn’t have happened during the flight. If this would have happened during the flight, there would have been redundant systems in place to take over to continued powered flight.

SLS Artemis 1 Core Stage being fired during it’s short hot fire test. Courtesy: NASA

When the CAPU was shut down due to the exceeded parameters, the systems instantaneously switched over to the backup units before the computer shut down the test while proving that the backup system works which would have saved the mission if it was flying.

Something you hear after every problem that shows up during testing is “This is why we test” and we heard that plenty during the post-test press conference and yesterday. Not much was known at the time and was able to be told during the post-test press conference on Saturday, but during the teleconference held with reporters on Tuesday more details could be shared.

We learned of three possible issues found during the hot fire test last Saturday:

  • An MCF or Major Component Failure call that was heard over the mission control audio
  • A possible flash of some sort that occurred around the engines prior to shut down
  • And the early shut down itself

John Honeycutt, NASA Program Manager of the Space Launch System, stated that the MCF callout was due to a sensor issue and had no connection to any actual component failing. He added that the heat blankets around the engines did their job while showing no signs of extra scorching. Finally, the last issue was explained in a statement made yesterday.

While the issues now have explanations, the teams and contractors of the SLS rocket are still continuing to go over the data to make sure they fully understand what happened during the hot fire to determine how to move forward. We learned during the call on Tuesday that the Core Stage has a limitation of being fueled with cryogenic propellant just nine times, which includes the fueling for launch.

Currently, the Core Stage for Artemis 1 has been fueled three times: during two wet dress rehearsals and during the Hot Fire test. It was mentioned that when the Core Stage arrives at Kennedy Space Center, it will go through another wet dress rehearsal which leaves NASA with just five more fueling operations for tests and launch attempts.

It’s concerning that the Core Stage is already nearing half of its cryo-cycle limit, but both NASA Associate Administrator Kathy Lueders and (at the time of the press conference) NASA Administrator Jim Bridenstine are confident in still being able to launch Artemis 1 by the end of this year.

The decision of how to move forward will now go to the next NASA leadership team.

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