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The static test-firing on January 16 also provided the SLS Core Stage team with their first opportunity to validate their current assumptions and predictions about how the vehicle would behave as an integrated stage in launch-like conditions. The partially-completed test-firing demonstrated the beginning and ending of a static-fire, but was stopped after only a minute of run-time on the engines.<\/p>\n
The four Core Stage engines were started at T-6.6 seconds as they will be during a launch. After the simulated liftoff at T0, they throttled up to the new SLS full power setting of 109%. At T+60 seconds, the first of three test objectives started with the stage\u2019s hydraulic thrust vector control (TVC) system gimbaling all four engines simultaneously.<\/p>\n
The first \u201cpower steering\u201d test in the Hot-Fire had the stage turning its proverbial steering wheel as fast as possible at the top end of the stage\u2019s gimbal requirements. When in motion, it\u2019s generally a bad idea to make the sharpest turn you can while moving at high speed, but given the opportunity in a static test stand, the controlled laboratory experiments would help evaluate the real-world behavior of the firing stage.<\/p>\n
The stage\u2019s four veteran Aerojet Rocketdyne RS-25 engines were running again for the first time since fulfilling their duties during their last Space Shuttle launches, but it was the first time a Core Stage was firing them in an SLS environment. Objectives of the static gimbal tests included running the TVC systems and the hydraulics supporting them within their designed operating envelope, but closer to the outside than the middle for some parameters.<\/p>\n
One second after the first \u201cTVC check\u201d started, test limits were violated, and as programmed, the SLS flight computers running at the top of the Core Stage shut down the engines, aborting the rest of the Hot-Fire.<\/p>\n
\u201cIt was actually two parameters, low hydraulic reservoir fill percentage and a low hydraulic return pressure or suction pressure. And the combination of those two initiated the CAPU (Core Auxiliary Power Unit) to shutdown,\u201d Jonathan Looser, NASA SLS Core Stage Propulsion Lead, said, referring to hydraulic system 2. \u201cIt is believed that the gimbal test is what pushed us below the lower limit that caused the shut down. And that gimbal test is intentionally stressing the hydraulic system to its maximum required rate, and that drove us just below the lower limit.\u201d<\/p>\n
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Credit: Brady Kenniston for NSF.<\/p>\n
(Photo Caption: The flight article for Artemis 1, Core Stage-1, fires in the B-2 position of the B Test Stand at Stennis Space Center on January 16. The Hot-Fire was cut short after 67 seconds of engine runtime when the stage\u2019s hydraulic performance fell below conservative limits just as the engines were being aggressively gimbaled for the first time in the test.)<\/em><\/p>\n The three flight computers run a special Core Stage-only, Green Run variation of the NASA-developed SLS flight software, and the Mission and Fault Management algorithms in the software look at data from different avionics boxes distributed throughout the stage. There are four Thrust Vector Control Actuator Controllers (TAC) in the engine section, with one paired with each hydraulic system.<\/p>\n \u201cThese particular [parameters], they flow through the TAC, so we see them as the flight software interrogates the TAC either with commands and just general health and status information every 20 milliseconds or 50 Hertz,\u201d Dan Mitchell, NASA\u2019s Technical Lead for SLS Avionics and Software Engineering, said.<\/p>\n The hydraulic system limit violations triggered a flurry of activity and commands, with the shutdown of CAPU 2 triggering commands to both compensate for the capability lost and to shutdown the engines and abort the test. For the Hot-Fire test, the commands to abort were issued in the processing cycle just 20 milliseconds after the auxiliary power unit was shutdown.<\/p>\n \u201cWe got the indication of those two violations, we initiated first the safing of CAPU 2 and then quickly followed in the next [processing] frame with beginning the safing of the stage itself, which includes sending shutdown commands to the engines,\u201d Mitchell explained.<\/p>\n The hydraulics in the stage are used for both the TVC power steering and for controlling the engine power settings. The Core Stage has redundancy in its TVC hydraulics, so when CAPU 2 was shutdown, the speed of two of the other CAPUs was increased to handle the gimbaling needs of four engines with only three CAPUs.<\/p>\n \u201c[With] the cross-strapping between the TVC actuators, you can lose one whole system and the adjacent systems will [compensate],\u201d Looser noted. \u201cImmediately after that, as a part of the logic of the adjoining two systems, CAPUs 1 and 3, those systems increased to 105%. And that\u2019s part of the redundancy in the system that the adjoining hydraulic systems can take over and power the actuators for the system that has been shut down.\u201d<\/p>\n<\/p>\nSee Also<\/h4>\n
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