Zoom / The NASA Space Launch System rocket, reflected in the back pool at the Kennedy Space Center in Florida, is launched for the fourth wet dress rehearsal attempt on June 6, 2022.
Trevor Mulman
NASA tried three times in April to complete a critical refueling test on its large Space Launch System rocket. And three times, due to about half a dozen technical problems, the space agency failed.
So NASA made the difficult decision to return the large rocket to the building assembly building for repairs, adding several months of delay to the program, which is already behind schedule. After this work was completed in early June, NASA returned the SLS rocket and the Orion spacecraft back to the launch site for a fourth attempt.
The painful decision turned out to be the right one. For more than 14 hours on Monday, NASA largely succeeded in completing this refueling test by refueling hundreds of thousands of gallons of liquid oxygen and hydrogen in the first and second stages of the SLS rocket.
“It’s been a long day for the team, but I think it’s been a very successful day for the team,” said Charlie Blackwell-Thompson, Artemis’ director of startup.
She and other NASA staffers joined a conference call with reporters on Tuesday to discuss the results of the fourth wet dress rehearsal test, which aims to work out the distortions in the rocket’s countdown to take-off before the day of launch. To this extent, the test seems to work to a large extent. NASA reached the T-29 seconds after takeoff during the test, close to the planned target of T-9.3 seconds, before completing the test just before starting the rocket’s four main engines.
During the teleconference, NASA officials declined to answer specific questions about whether a fifth test would be needed – to reduce the countdown to T-9.3 seconds – or when the rocket could be ready for its debut launch. Referring to their desire to review more data, officials said they expect to provide this information in a few more days. However, their comments suggested that employees could rely on a fifth test.
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A handful of technical problems arose during the test on Monday, the most significant of which was a hydrogen leak in a quick disconnection at the bottom of the mobile launch tower that supports the SLS rocket during loading. This 4-inch hydrogen line is one of several that were released from the rocket just before takeoff and connected to the tower’s tail service mast.
NASA failed to resolve the leak seal problem during the final part of Monday’s test, so instead it chose to mask the leak from the ground launch sequencer, the ground-based computer that controls most of the countdown. This did not pose a risk to the missile during the test, but will need to be corrected before the actual launch.
With this little disguise, NASA’s launch team was able to go from T-10 minutes to T-29 seconds and demonstrate the ability not only to fill the SLS rocket, but also to keep the fuel tanks refilled. When the ground launch sequencer is transmitted to the rocket’s on-board computer for the last part of the countdown, the flight computer automatically terminates the countdown.
NASA staff liked what they saw. “This is the first time we are in a completely cryogenic environment, both at the main and the upper stage,” said Blackwell-Thompson. “Terminal counting is a very dynamic time. I totally expected that we might have one or two things we might need to talk about in terms of the number of terminals, but it was extremely smooth. There was nothing to talk about.”
This refueling test is the latest major hurdle between the SLS rocket and the launch attempt later this year. There is still work to be done and the agency has to decide if another test for wet clothes is needed. But Mike Sarafin, head of the Artemis I mission, said he believed NASA had met about 90 percent of the test targets to date.
In addition to fixing the leaky hydrogen seal, NASA still has to return the rocket back to the vehicle assembly building to install and arm the take-off system. This work probably precludes an attempt to start before the end of September.
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