NASA attempted three times in April to complete a critical fuel test of its large Space Launch System rocket. And three times, due to about half a dozen technical problems, the space agency failed.
And so NASA made the difficult decision to take the big rocket back to the Vehicle Assembly Building for repairs, adding a few months of delays to a program that was already years behind schedule. After that work was completed in early June, NASA took the SLS rocket and the Orion spacecraft back to the launch pad for a fourth attempt.
The painful decision turned out to be the right one. Over the course of more than 14 hours on Monday, NASA was able to complete this fueling test, loading hundreds of thousands of gallons of liquid oxygen and hydrogen into the first and second stages of the SLS rocket.
“It was a long day for the team, but I think it was a very successful day for the team,” said Charlie Blackwell-Thompson, director of launch for Artemis.
She and other NASA officials joined a conference call with reporters on Tuesday to discuss the results of the fourth “wet suit test” test, which aims to resolve the rocket’s countdown to takeoff before launch day problems. To that extent, the test seemed to largely work. NASA arrived at T-29 seconds of liftoff during the test, close to its intended target of T-9.3 seconds, before ending the test just before igniting the rocket’s four main engines.
During the conference call, NASA officials declined to answer specific questions about whether a fifth test would be needed — to bring the count down to T-9.3 seconds — or when the rocket might be ready for its maiden launch. Citing a desire to review more data, officials said they hoped to provide that information in a few more days. From their comments, however, it appeared that officials may be leaning against a fifth test.
A handful of technical issues occurred during Monday’s test, the most significant of which was a hydrogen leak from a quick disconnect at the bottom of the mobile launch tower that supports the SLS rocket during fueling. This 4-inch hydrogen line is one of several that are released from the rocket shortly before liftoff and are connected to the tower’s tail service mast.
NASA was unable to resolve the issue with a leaky seal during the latter part of Monday’s test, so it chose to mask the leak from the ground launch sequencer, the ground-side computer that controls most of the countdown. . This posed no risk to the rocket during testing, but would need to be fixed before an actual launch.
With that little bit of masking, the NASA launch team was able to go from T-10 minutes to T-29 seconds and demonstrate the ability to not only fill the SLS rocket, but also keep its fuel tanks topped up. When the ground launch sequencer passed to the rocket’s on-board computer for the final part of the countdown, the flight computer automatically ended the countdown.
NASA officials liked what they saw. “This is the first time we’ve been in a fully cryogenic environment in both the mid-stage and upper stage,” Blackwell-Thompson said. “End count is a very dynamic time. I was hoping we would have one or two things we might need to talk about in the end count, but it was extremely smooth. There was nothing to talk about.”
This supply test is the final big hurdle between the SLS rocket and a launch attempt later this year. There is still work to be done, and the agency needs to decide whether another wet suit test is needed. But Mike Sarafin, manager of the Artemis I mission, said he believed that, to date, NASA had completed about 90% of the test’s objectives.
In addition to fixing the leaking hydrogen seal, NASA still needs to get the rocket back to the Vehicle Assembly Building to install and arm the flight termination system. This work likely precludes an attempt to launch before the end of September at the earliest.
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