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Engineers blame 'intentionally conservative' test parameters for premature end to Space Launch System hotfire

'If this scenario occurred during a flight, the rocket would have continued to fly'

After the weekend's shorter-than-hoped-for test firing of the core stage of NASA's monstrous Space Launch System (SLS) rocket, engineers have confirmed the hardware remains in "excellent condition" and blamed "test parameters that were intentionally conservative."

The parameters were designed for ground testing and were exceeded by a hydraulic system during gimballing by thrust vector control hardware, resulting in the shutdown. "If this scenario occurred during a flight," the agency explained, "the rocket would have continued to fly using the remaining CAPUs [Core Stage Auxiliary Power Units] to power the thrust vector control systems for the engines."

"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," added the agency. Alas, the intentional stressing of the system that resulted in the CAPU shutdown (and transfer of power to the other CAPUs) exceeded those pre-sets and triggered the premature end of the hotfire.

"The data is being assessed as part of the process of finalizing the pre-set test limits prior to the next usage of the core stage."

And that alarming Major Component Failure (MCF) call? It was due to the loss of one leg of redundancy in the instrumentation of Engine 4. In addition, the engines managed to hit their full power of 109 per cent during the test.

However, and here lies the rub, there is no escaping the fact that 67.2 seconds is quite some way short of the eight minutes engineers aimed for. While the initial findings will provide a little relief for the troubled Artemis programme and its schedule constraints, they do not yet justify ditching a second test and shipping the stage to Kennedy Space Center.

"Data analysis is continuing to help the team determine if a second hotfire test is required," said the agency. Those parameters around the thrust vector control can be tweaked by the team to prevent another automatic shutdown should the decision be taken to run the test again.

However, going for a second test would severely damage the already slim chances of a 2021 launch for the uncrewed Artemis I. ®

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