The long-awaited Green Run for the Space Launch System Core Stage occurred on January 16th. The test was set for the afternoon, and after several delays, the 4 RS-25’s on the Core Stage finally ignited. They began what was supposed to be a 480-second burn, but the engines shut down after only 67.2 seconds. This was at the point where the stage computer was to start commanding the engines to go through Thrust Vector Control (TVC) checks, moving the engines around. Just before the moment of the shutdown, an engineer could be heard saying “MCF on Engine 4”. After the test abort, Wayne Hale, the last Shuttle Program Manager, took to Twitter to explain that MCF means Major Component Failure. “MCF means time to end an engine firing,” according to Hale.

It turns out the actual reason why the engines shut down had nothing to do with the MCF on Engine 4. According to a NASA blog update published on Jan 19th, the actual reason for the aborted firing was that one of the engine’s TVC systems exceeded its pre-set limits. The limit was intentionally set low to keep the vehicle safe during the ground firing and would not have resulted in a shutdown in flight, according to NASA.

This particular engine is actually the Core Stage they plan to use for the Artemis I first mission, which is set to go all the way to the Moon. This means that they are taking it easy during testing, trying very hard to preserve their hardware.

Before the test, NASA said that they needed at least 250 seconds of firing for a successful test. The test-firing had 23 objectives, and the 67.2 seconds of firing fully completed 15 of those objectives.

As of the update on January 19th, teams were still investigating whether a second Green Run was necessary to complete the objectives. The key to the decision is the fact that the SLS core stage is only designed to be tanked with its super-cold liquid hydrogen fuel a total of nine times. The vehicle has already been tanked three times, two wet dress rehearsals and the Green run. It will undergo another wet dress rehearsal when stacked at LC-39A, or Launch Complex 39-A, and will be fueled again at launch. All of these fuelings make it more difficult to decide whether to do another Green Run and as of press time a decision had not been made.

More Information

NASA blog

SpaceFlight Now article

Video