According to NASA today the reason the SLS static fire test cut off after only one minute was because of too conservative margins set in the computer software.
In an update today, however, NASA said it was engine 2 that caused the abort. At that moment, the engines were underdoing a gimble test where they are rotated in different directions just as they must do during ascent to steer the rocket. Actuators in the Thrust Vector Control system that generate the force to gimble an engine are powered by hydraulic Core Stage Auxiliary Power Units (CAPUs). The CAPUs for engine 2 exceeded pre-set test limits and the computer system automatically shut down the test as it was designed to do, but NASA said it would not have been a problem during a launch.
According to NASA’s update,
The specific logic that stopped the test is unique to the ground test when the core stage is mounted in the B-2 test stand at Stennis. If this scenario occurred during a flight, the rocket would have continued to fly using the remaining CAPUs to power the thrust vector control systems for the engines.
Note too that another issue during the test needs resolution:
Initial data indicate the sensor reading for a major component failure, or MCF, that occurred about 1.5 seconds after engine start was not related to the hot fire shutdown. It involved the loss of one leg of redundancy prior to T-0 in the instrumentation for Engine 4, also known as engine number E2060. Engine ignition begins 6 seconds prior to T-0, and they fire in sequence about 120 milliseconds apart. Test constraints for hot fire were set up to allow the test to proceed with this condition, because the engine control system still has sufficient redundancy to ensure safe engine operation during the test. The team plans to investigate and resolve the Engine 4 instrumentation issue before the next use of the core stage.
No decision has been made yet whether they will do another static fire test before shipping the core stage to Florida for launch. They are under a time limit, as they have begun stacking the SLS rocket’s strap-on solid rocket side boosters, and those only have a life expectancy of one year once stacking has begun.
As far as I am concerned, nothing about the development of this rocket makes sense. I would never fly on it no matter how much money was offered to me, and anyone who does must know the terrible risk they take.
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