After three previous aborted attempts, NASA successfully powered its new massive deep-space rocket, the space launch system, for the first time on Monday, completing a critical milestone before the vehicle’s first flight. However, there was a shadow over the achievement. The provision was part of an elaborate general rehearsal that ended 20 seconds earlier than NASA had anticipated, and it is unclear whether the agency obtained all the data and practice it needed to proceed with the debut launch of the rocket.
The space launch system, or SLS, is a key piece of NASA’s Artemis flagship program: an elaborate effort to send the first woman and the first person of color to the surface of the moon. But first, the SLS has to fly, and before that can happen, NASA wanted to do all the tricky steps that lead to a real launch, except the part where the rocket takes off.
With the SLS right on the launch pad at the Kennedy Space Center in Florida, NASA engineers and flight controllers filled the vehicle with ultra-cold thrusters on Monday, just as they would on launch day. With all SLS tanks full, the flight crew counted down to a simulated takeoff time, with the plan to stop the countdown to approximately 9 seconds. Instead, the team stopped the countdown to T-minus 29 seconds due to a hydrogen leak. NASA says it was able to complete most of its targets for the test, mostly by loading the vehicle with propulsion, but that there are still a handful that they were unable to reach with the premature cut.
“I would say most of our goals have been achieved.”
“I would say most of our goals were met,” Charlie Blackwell-Thompson, director of the launch of Artemis at NASA, said during a press conference after the test. “Maybe there were small pieces within that main goal that we fell a little short of.”
NASA has attempted this general rehearsal three times before, and all of these attempts were completed before flight controllers could fully charge the rocket with propulsion. After the third failed attempt, NASA introduced the SLS into the agency’s massive vehicle assembly building for various repairs and upgrades before rolling the rocket back onto the platform on June 6th.
Three of the most important objectives of the general test included demonstrating that the flight crew could load the vehicle with propellant, stop the countdown and then drain the fuel SLS, all of which was done on Monday. In addition, NASA was able to enter the terminal countdown, the final phase of the countdown that begins T-minus 10 minutes before launch.
NASA / Ben Smegelsky
One of the big things they couldn’t try was recycling. The team had initially planned to go down to T-minus 33 seconds, stop the count and then return to T-minus 10 minutes. This goal was to simulate an unexpected hold on release day and an attempt to retry it, which can sometimes happen. The team would then have dropped to T-minus 9.3 seconds, just before the sequence began to start the main engines at the base of the rocket.
Plans changed during the test. The simulated take-off was delayed for hours due to a number of issues that flight controllers worked on throughout the day, including a hydrogen leak. Ultimately, flight controllers chose to skip the stop and turn at T-minus 33 seconds and only go down to T-minus 9.3 seconds, according to CBS. However, they knew that the hydrogen leak would likely trigger an abortion inside the flight computers before reaching the final countdown time.
“We will make a decision on what is the best way forward.”
During a post-test press conference, NASA staff noted that most of the objectives of the general rehearsal were met. “I’d say we’re in the 90th percentile in terms of, you know, where we should be in general,” said Mike Sarafin, manager of the Artemis mission at NASA. But they were vague about the elements that were not completed. One of the goals they failed to achieve was to demonstrate something known as “bleeding flow,” a way to maintain proper propellant temperatures, due to hydrogen leakage. There was also some old hardware in the solid rocket propellants that did not have a chance to fire as planned.
Now, NASA says it is looking at the data it collected and will determine the next steps. “I think it’ll take us a couple of days to get over it, and then we’ll make a decision on what is the best way to go,” said Tom Whitmeyer, NASA’s associate associate administrator for common exploration systems. The agency may choose to do another type of power test, and Jim Free of NASA, NASA’s associate administrator for the development of exploration systems, said before this attempt that the NASA wanted a thorough test before flying. “This is the first time we want this vehicle and I think we need to understand everything we can before we commit to launching it,” Free said last week. But Whitmeyer noted that there is “a relative risk of continuing to operate the hardware on the bearing.”
As to how this might affect the timeline for the first flight of the SLS, NASA will not say. SLS is scheduled to debut during a flight called Artemis I, which will see the rocket launch an empty crew capsule called Orion around the Moon in a few weeks’ journey. Prior to this general rehearsal, NASA noted that the first likely launch attempt would be during a window that opened in late August. Now, with this test, NASA does not set a firm date. “I don’t think we know it yet,” Whitmeyer said. “We have to really sit down and do everything we just talked about: look at the goals, see what we’ve achieved, and see what extra work might be required.”