NASA executives consider largely successful moon rocket test

It took NASA four attempts to fully fuel the new Space Launch System moon rocket, and while new issues surfaced during Monday’s most recent practice countdown, senior executives said they were pleased with the giant booster’s performance.

“We think we’ve had a really successful rehearsal,” Tom Whitmeyer, deputy chief of NASA Exploration Systems Development, said Tuesday. “We know we’re going to have a handful of points that we need to address… and I think we’re going to take a few days to get through that and then we’ll make a decision on the best way forward.”

Assuming the repair of a leaking hydrogen fitting is successful, managers may decide to run yet another tank test, or they may conclude that they now have enough data to launch a late summer launch campaign with no time to spare. losing to a new dress rehearsal could only bring about an incremental improvement.

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The full moon sets behind the Space Launch System moon rocket on June 15 at Kennedy Space Center.

William Harwood/CBS News


During a conference call Tuesday with reporters, Whitmeyer and other senior executives would not speculate about what comes next. But Mike Sarafin, the mission manager for the Artemis lunar program at NASA headquarters, said the SLS rocket has now achieved most of the agency’s pre-flight targets, despite not quite reaching the end of Monday’s practice countdown. has come.

As it was, the team made T-minus 29 seconds – just 20 seconds from target – and engineers understand what caused the early stoppage.

“I’d say we’re in the 90th percentile of where we need to be globally,” Sarafin said. But “there are still some outstanding points that we need to look at… to say we’re ready from a flight rationale point of view.”

Years behind schedule and billions over budget, NASA is in the final stages of testing the giant SLS rocket and its complex systems before launching it on the program’s maiden flight: an unmanned Orion crew pod on a fly past the moon and back.

To clear the way for launch, NASA fired the rocket’s first stage motors in March 2021, shipped the stage to the Kennedy Space Center in Cape Canaveral, Florida, attached it to a pair of Northrop Grumman solid fuel boosters, added an upper stage from United Launch Alliance, then attached an Orion crew pod built by Lockheed Martin.

The 330-meter-tall rocket, the most powerful ever built for NASA, was taken from the iconic Vehicle Assembly Building to launch pad 39B in March for a practice countdown and tank test, one of the last major milestones on the road to launch.

The goal was to load the rocket with 750,000 gallons of super-cold liquid oxygen and hydrogen fuel, then count down to T-minus 9 seconds, the point at which the engines would begin firing during an actual launch, to operate complex computer systems, software, and hardware. flying day conditions.

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The missile and its target.

William Harwood/CBS News


In addition to attempting to run through a normal countdown, the team also planned to test the ability to stop the clock and recycle: to make sure the system can handle issues that could include a last-second delay. cause during an actual countdown.

But a frustrating series of mostly ground system problems, along with a hydrogen leak in a fuel line fitting, problems with a seized second stage helium valve, and a shortage of gaseous nitrogen used in fire prevention systems, derailed three refueling attempts in a row.

The missile was transported back to the VAB for repair and then back to the pad earlier this month. During Monday’s fourth tank test, engineers were finally able to fully charge the SLS, pumping 750,000 gallons of oxygen and hydrogen into the four tanks that make up the first and second stages.

But before the tanks were full, engineers discovered a new problem: a leaking 4-inch hydrogen quick coupler. The system is used to route hydrogen through the four RS-25 first stage engines to properly cool or condition them before ignition.

The ground launch sequencer computer running the countdown monitors thousands of parameters, including the status of the 4-inch “bleed line,” and is programmed to stop the clock if the specifications described in the takeoff capture criteria are violated.

When the vent line problem surfaced Monday, engineers had to quickly figure out a way around the problem so they could continue charging propellant and in what’s known as “stable replenishment,” constantly filling the tanks with hydrogen. and oxygen warm and boil off.

They managed to do that by instructing computers to ignore sensor readings that would have indicated a leak, and the team eventually got all four tanks fully loaded. That set the tone for the final phase of the countdown, the action-packed last 10 minutes before launch. Or, in this case, in the run-up to a computerized shutdown.

The original goal was to count down to T-minus 33 seconds, the point at which the ground computer would transfer to the SLS’s onboard software, and then recycle back to T-minus 10 minutes. The idea was to test the system’s ability to recover from a problem. The plan then called for the count to resume and go all the way to T-minus 9.3 seconds.

But because of the leaky quick-disconnect fitting in the hydrogen bleed line and lost time troubleshooting, managers chose to forgo recycling after 33 seconds and continue the countdown beyond transfer to the missile’s flight computer.

While the ground computer could be told to ignore the sensors indicating a leak, the flight computer’s software couldn’t be easily modified, and launch director Charlie Blackwell-Thompson said engineers expected the countdown to stop once it took over.

“We certainly have the ability within the ground launch sequencer to inhibit monitoring of those kinds of parameters, but we have fewer capabilities on the flight side for that,” she said. “And so we knew that once it sensed that condition, we’d have a shutdown.”

And that’s exactly what happened. The countdown stopped at T-minus 29 seconds, four seconds after the transfer occurred.

What happens next is not yet clear. The next realistic moon launch period, based on the movements of the Earth and the moon and the planned trajectory of the Orion capsule, will begin on August 23. Another fuel test could take the flight further, but NASA hasn’t discussed launch dates yet.

In the meantime, Blackwell-Thompson said, “You’re following the data. And so we’re going to collect the data, and we’ll see where the data takes us.”

Editor’s Note: An earlier version of this story incorrectly stated which company produced the solid fuel boosters.

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