It took four attempts by NASA to fully fuel the Space Launch System’s new lunar rocket, and while new problems emerged during the latest countdown on Monday, senior managers said they were satisfied with the giant booster’s performance.
“We think we’ve had a really successful trial,” Tom Whitmeyer, NASA’s deputy head of Exploration Systems Development, said Tuesday. “We know we’re going to have a handful of items that we need to sort out… and I think we’ll take a few days and get through that and then we’ll make a decision on what’s the best way forward.”
Assuming repairs to a hydrogen leak are successful, managers may decide to conduct another fueling test of some sort, or they may conclude that they have enough data now to jump into a late summer launch campaign without wasting time on another dress rehearsal that can only provide incremental improvements.
During a conference call on Tuesday with reporters, Whitmeyer and other senior managers did not speculate about what comes next. But Mike Sarafin, mission manager for the Artemis lunar program at NASA Headquarters, said the SLS rocket has already accomplished most of the agency’s pre-flight objectives, despite not making it to the end of Monday’s countdown.
As it was, the team got to T-minus 29 seconds – just 20 seconds short of the goal – and the engineers understand what caused the initial cut.
“I would say we’re in the 90th percentile in terms of where we need to be overall,” Sarafin said. But “there are still some open items that we need to look at … to say that we are ready from a flight logic point of view.”
With 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 unmanned crew capsule on a flight beyond from the moon and back.
To clear the way for launch, NASA’s test fired the rocket’s first stage engines in March 2021, sent the stage to the Kennedy Space Center in Cape Canaveral, Florida, attached it to a pair of Northrop solid-fuel thrusters. Grumman, added a United Launch Alliance upper stage and 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 hands-on countdown and refueling test, one of the last major milestones on the way to the release .
The aim was to load the rocket with 750,000 gallons of supercold liquid oxygen and hydrogen fuel and then count down to T-minus 9 seconds, the point at which the engines would start igniting during an actual launch, to test complex computer systems. , software and hardware in flight conditions.
In addition to trying to run 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 might force a last-second delay during an actual countdown.
But a frustrating series of problems primarily in the ground system, along with a hydrogen leak in a fuel line connection, problems with a stuck second stage helium valve, and a deficit of nitrogen gas used in fire prevention systems, derailed three consecutive refueling attempts. .
The rocket was transported back to the VAB for repairs and then back to the block earlier this month. During its fourth fueling 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 4-inch hydrogen quick-connect leak. The system is used to direct hydrogen through the four RS-25 first stage engines to properly cool or condition them before ignition.
The ground launch sequencer computer that performs 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 outlined in the launch confirmation criteria are violated.
When the bleed line problem arose on Monday, engineers had to quickly find a way around the problem so they could continue loading propellant and go into what’s known as “stable replenishment”, constantly filling the tanks as hydrogen and oxygen. heat and boil.
They were able to do this by instructing the computers to ignore sensor readings that would indicate a leak, and the team eventually loaded all four tanks fully. This set the stage for the final phase of the countdown, the action-packed final 10 minutes leading up to 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 at which the ground computer would pass to the SLS’s onboard flight 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 resuming the count and continuing to T-minus 9.3 seconds.
But on Monday, because of the leaking quick-disconnect connection on the hydrogen bleed line and wasted time troubleshooting, managers chose to forgo recycling in 33 seconds and continue the countdown after delivery to the rocket flight.
While the ground computer can be instructed to ignore sensors that indicate a leak, the flight computer’s software cannot be easily modified, and launch director Charlie Blackwell-Thompson said engineers expected him to stop counting. regress as soon as it took control.
“We certainly have the capability within the ground launch sequencer to inhibit monitoring of these types of parameters, but we have less capability on the flight side for that,” she said. “And so we knew that once I felt 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 handoff took place.
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, begins on August 23. Another fueling test could take the flight beyond that, but NASA has yet to say launch dates.
Meanwhile, Blackwell-Thompson said, “You follow the data. And then we’re going to collect the data and see where the data takes us.”
Editor’s Note: An earlier version of this story misrepresented which company made the solid fuel boosters.