NASA to conduct the second Green Run SLS assessment

NASA will take out a second core process hotfire evaluation of the Space Launch System, a step that renders the spacecraft more likely to miss its expected launch date late this year. NASA announced late January 29 that the static-fire evaluation of the four RS-25 engines of the core stage would be re-run at Stennis Space Center in Mississippi no sooner than the final week of February. In the Green Run evaluation campaign, which began a year ago, this test is the last move. Since the original hotfire test on January 16 finished after just about 67 seconds, the agency agreed to conduct a second test, well short of the expected 485 seconds. Three days later, NASA stated that hydraulic system hit Engine 2 ‘purposely conservative’ restrictions, causing the flight machine to shut down.

For the upcoming drill, engineers would “update restrictive control logic criteria that culminated during the first hot-fire evaluation being terminated earlier than planned by the flight computer,” NASA stated. An electrical harness which caused a “massive part failure” alert in Engine 4 throughout the evaluation had already been replaced but included redundant instrumentation not related to the early conclusion of the test. The upcoming evaluation will span “possibly at least four minutes,” while a full-duration evaluation remains the target. Officials with NASA as well as Boeing, SLS main contractor, stated before the first static-fire evaluation that they would gather much of the data they wanted if the test lasted around 250 seconds or just over 4 minutes.

Agency officials indicated that it could be necessary to continue plans for the Artemis 1 launch without the need for a second hotfire evaluation at a January 19 meeting about the mission, despite dropping short of the needed duration. Kathy Lueders, who works at NASA Agency as an Associate Administrator in charge of Human Exploration and Activities, stated, “You have to evaluate the consequences of opening the flight core phase to yet more evaluations, and how that risk interacts with the training we need to do.”

The core stage might be more stable than they anticipated, however. Then-NASA Administrator Jim Bridenstine stated at the conference that the core process was planned to be filled just 9-times with liquid hydrogen, liquid oxygen, and cryogenic propellants. An extra static-fire test will slash the margin used by testing at the Kennedy Space Center, as well as launch attempts using two of those fuels previously used for the hotfire analysis as well as an earlier wet dress test. On January 2NASA stated, that the core process is only classified for the 22 fueling cycles, 9 of which are designated for the Green Run evaluation campaign.