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SLS static fire abort not caused by malfunction but too-tight parameters

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.

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.

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  • Doubting Thomas

    Seems like another “software” issue. Lots of these under Boeing: 747 Max, Starliner OFT-1 and now this, too narrow test parameters inputted into test monitoring equipment.

    Seems like you could have checked that out before what had to be a many millions of dollar test.

    Still have much sympathy for the average engineer / tech that is busting their hump to make this all succeed.

  • Tom

    I can’t imagine them not performing the entire 8 minute burn before heading for the cape. There is just too much at stake including whats left of marginal reputations.

  • Dick Eagleson


    That makes excellent sense. Which is probably the leading reason to expect that it will not, in fact, be done.

  • Alton

    Is this the New NASA?

    Where manrating a system involves the number of coffins required………

  • David Eastman

    At this point I expect there will be several more “well it didn’t do what we expected, but it’s got redundancy and the tests are harder than they need to be” moments, and that, barring something truly “no, we can’t possibly hand-wave this away” they’ll launch anyways. And if it succeeds, they’ll call it a triumph. And if it fails, I expect there to be a circular firing squad as everyone blames everyone else, and in the end nobody will really pay any price.

  • Mitch S.

    35 years ago NASA management was feeling the pressure.
    The Space Shuttle that was promised to provide reliable, economic transport to space had gone way over budget, and years after the first flight had managed only 24 launches.
    Criticism was building. The Shuttle looked like a hopelessly complex, fussy system prone to countless delays and blown schedules.
    NASA managers needed to show the system was maturing. They came up with an idea to launch a civilian teacher into space, to tie into classrooms around the world, to demonstrate how the Shuttle has advanced space exploration and it would be unthinkable to threaten it’s budget when it was on the threshold of realizing it’s original mission.

    But now that mission had been delayed multiple times providing fuel for the critics.
    How could another launch date be scrubbed just for a bit of cold weather?
    Sure there had been damage to o-rings in warmer weather but that won’t be a problem during launch, if one o-ring fails surely the second will work “as it was designed to do”…
    Time for NASA to be “run like a business and not like a great engineering firm”.
    Damn the data, full speed ahead!

  • eddie willers

    How could another launch date be scrubbed just for a bit of cold weather?

    God bless Richard Feynman. He simply sat at the commision table, dropped a wad of the O-Ring material in his glass of ice water, pulled it out tried to mash it with his fingers. Nothing more needed to be said.

    I sure wish he was around today. He’d make short work of those “climate” experts!

  • Icepilot

    Why wouldn’t you write test software to perform the same as in flight? Hell, why wasn’t the test software written to induce every failure that the system is designed to accommodate in real flight? You know, to see if it actually works.

  • Edward

    Icepilot asked: “Why wouldn’t you write test software to perform the same as in flight? Hell, why wasn’t the test software written to induce every failure that the system is designed to accommodate in real flight? You know, to see if it actually works.

    I’m not sure that any of these would have helped in this test. Often during initial testing, parameters are set tighter than believed necessary in order to make sure that the tests don’t do physical damage to the hardware. As engineers gain confidence in the hardware, the parameters are opened up. In this case, the tight parameters bit them in the schedule butt rather than the hardware butt.

    Software is often tested separately from the hardware in order to test a great many anticipated failure modes. By the time it is controlling flight hardware the engineers should already have confidence that it behaves as expected. Once the engineers understand the software and the hardware, they are ready for tests such as the one they performed on Saturday the 16th. On Saturday, they ran into an unanticipated condition.

    On the other hand, software development and testing depends heavily on the corporate philosophy and culture as well as on the software maturity model level used.

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