SLS: Nasa’s ‘megarocket’ engine test ends early

The RS-25 engines are the same type that powered the space shuttle orbiter

Shortly before 22:30 GMT (17:30 EST) on Saturday, the four engines ignited, burning for more than a minute before the event was aborted.

The core stage of the the Space Launch System (SLS) was being evaluated at Stennis Space Center, in Mississippi.

The engines were supposed to fire for eight minutes to simulate the rocket’s climb to orbit.

The SLS is part of Nasa’s Artemis programme, which aims to put Americans back on the lunar surface in the 2020s.

When it makes its maiden flight – possibly later this year – the SLS will become the most powerful rocket ever to have flown to space.

Teams at Stennis are still poring over the data to find out what happened. John Honeycutt, SLS program manager at Nasa’s Marshall Space Flight Center in Alabama, said there were “a lot of dynamics going on” when the engine shut down.

The engines’ power levels were being throttled down and up again; they were also being prepared to pivot – or gimbal. This movement allows the rocket to be steered during flight.

“We did see a little bit of a flash come from around the interface between the thermal protection blanket on engine four at the time when we had initiated the gimbal,” Honeycutt told reporters at a post-test briefing at Stennis.

The as-yet unknown problem triggered what Nasa calls a failure identification (Fid), followed by a major component failure (MCF). As a result of the fault, an onboard computer known as the engine controller sent a message to another computer called the core stage controller, which took a decision to shut down the vehicle.

“Any parameter that went awry on the engine could have sent that failure ID,” said John Honeycutt.

It was the first time all four RS-25 engines had been ignited together, in a test known as a “hotfire”.

The core stage of the rocket was anchored to a massive steel structure called the B-2 test stand on the grounds of the Stennis facility.

This was the eighth and final test in the Green Run, a programme of evaluation carried out by engineers from Nasa and Boeing – the rocket’s prime contractor.

They wanted to iron out any problems before the core stage is used for the first SLS launch, in which it will send Nasa’s next-generation Orion spacecraft on a loop around the Moon.

Nasa’s outgoing administrator Jim Bridenstine declined to call Saturday’s event a failure: “This is why we test,” he said, adding: “Before we put American astronauts on American rockets, that’s when we need it to be perfect.”

Officials have not yet decided whether to re-run the hotfire, or proceed with shipping the core stage to Kennedy Space Center (KSC) in Florida to prepare it for the rocket’s uncrewed maiden flight, a mission called Artemis-1.

“It depends what the anomaly was and how challenging it’s going to be to fix it,” said Bridenstine.

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