It took four tests for NASA to fully power the new Space Launch System moon rocket, and while new issues surfaced during the latest practice countdown on Monday, senior executives said they were pleased with the performance of the giant booster.
“We think we had a really successful rehearsal,” Tom Whitmeyer, NASA’s deputy chief of exploration systems development, said Tuesday. “We know we’ll have a handful of things that we need to deal with…and I think we’ll take a few days and work through that and then make a decision on the best way forward.”
Assuming repairs to a leaking hydrogen fitting are successful, officials might decide to perform some other refueling test, or they might conclude that they now have enough data to embark on a refueling campaign. launch at the end of the summer without wasting time on another dress rehearsal which may only bring incremental improvement.
In a conference call Tuesday with reporters, Whitmeyer and other top executives declined to speculate on what’s next. But Mike Sarafin, mission manager for the Artemis lunar program at NASA Headquarters, said the SLS rocket has now met most of the agency’s pre-flight goals, although it did not meet the end of the countdown to Monday’s workouts.
As it stands, the team is down to T-minus 29 seconds – just 20 seconds from goal – and engineers understand what caused the early cut.
“I would say we’re in the 90th percentile as far as where we need to be overall,” Sarafin said. But “there are still open elements that we need to examine … to say that we are ready from the point of view of justifying the flight.”
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: sending an Orion crew capsule unpiloted on a flight beyond the moon and back.
To pave the way for launch, a NASA test fired the rocket’s first-stage engines in March 2021, shipped the stage to Kennedy Space Center in Cape Canaveral, Fla., strapped it to a pair of Northrop Grumman solid-fuel boosters, added an upper stage from United Launch Alliance, then attached an Orion crew capsule, built by Lockheed Martin.
The 330-foot-tall rocket, the most powerful ever built for NASA, was transported from the iconic Vehicle Assembly Building to Launch Pad 39B in March for a practice countdown and a refueling test, one of the last big steps 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 when the engines would begin to fire during a launch. real, to test complex computer systems, software and hardware under day flight conditions.
As well as attempting to cycle through a normal countdown, the team also planned to test its ability to stop the clock and recycle: to ensure the system can handle issues that could force a last-second delay. during a real countdown.
But a frustrating series of problems mainly related to the ground system, as well as a hydrogen leak in a fuel line connection, problems with a stuck second stage helium valve and a lack of nitrogen gas used in fire prevention systems, derailed three consecutive refueling attempts. .
The rocket was taken back to VAB for repairs and then returned to the pad earlier this month. During its fourth refueling test on Monday, 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-disconnect fitting. The system is used to route hydrogen through the four RS-25 first stage engines to cool or condition them properly before ignition.
The ground launch sequencer’s computer running the countdown monitors thousands of parameters, including the status of the 4-inch “purge line”, and is programmed to stop the clock if the specifications outlined in the launch engagement criteria are violated.
When the bleed line problem surfaced on Monday, engineers had to quickly find a way around the problem so they could continue propellant loading and enter what’s known as a “stable fill,” constantly filling the hydrogen and oxygen tanks. reheat and boil.
They managed to do this by having the computers ignore sensor readings that would have indicated a leak, and the team eventually managed to fully charge all four tanks. This set the stage for the final phase of the countdown, the action-packed final 10 minutes before launch. Or, in this case, leading to a computer-controlled cut.
The original goal was to count down to T-minus 33 seconds, the point where the ground computer would transition to the SLS on-board flight software, and then back to T-minus 10 minutes. The idea was to test the ability of the system to recover from a problem. The plan then was to resume the count and continue to T-minus 9.3 seconds.
But on Monday, due to the leaking quick-disconnect fitting in the hydrogen purge line and lost time troubleshooting, officials elected to forgo the 33-second recycle and continue the countdown after the transfer. to the rocket’s flight computer.
While the ground computer could be told to ignore sensors indicating a leak, the flight computer’s software could not be easily changed, and launch director Charlie Blackwell-Thompson said engineers s expected him to stop the countdown once he took over.
“We certainly have the capability in the ground launch sequencer to inhibit monitoring of these kinds of parameters, but we have less capability on the flight side for that,” she said. “And so we knew that once he detected that condition, we would have a cut.”
And that’s exactly what happened. The countdown stopped at T-minus 29 seconds, four seconds after the transfer.
What happens next is still unclear. The next realistic lunar launch period, based on the movements of the Earth and Moon and the planned trajectory of the Orion capsule, opens on August 23. Another refueling test could push the flight beyond that, but NASA has yet to set launch dates.
In the meantime, Blackwell-Thompson said, “You follow 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 made the solid fuel boosters.