NASA counts down to 29 seconds after launch of large SLS rocket

Enlarge / NASA’s Space Launch System rocket, reflected in the turning basin at Kennedy Space Center in Florida, rolls out for a fourth wetsuit rehearsal attempt on June 6, 2022.

Trevor Mahlman

NASA made three attempts in April to complete a critical refueling test of its large Space Launch System rocket. And three times, due to about half a dozen technical issues, the space agency failed.

And so NASA made the difficult decision to bring the big rocket back to the Vehicle Assembly Building for repairs, adding a few months to a schedule that was already years behind schedule. After that work was completed in early June, NASA brought the SLS rocket and Orion spacecraft back to the launch pad for a fourth test.

The painful decision turned out to be the right one. Over the course of more than 14 hours on Monday, NASA was largely successful in completing this refueling 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, Artemis Launch Director.

She and other NASA officials joined a conference call with reporters on Tuesday to discuss the results of the fourth “wetsuit rehearsal” test, which aims to address issues with the rocket’s countdown to liftoff. before launch day. To that extent, the test seemed to largely work. NASA came within T-29 seconds of liftoff during the test, close to its planned target of T-9.3 seconds, before ending the test just before igniting the rocket’s four main engines.

During the teleconference, NASA officials declined to answer specific questions about whether a fifth test was needed – to bring the count down to T-9.3 seconds – or when the rocket might be ready. for its first launch. Citing a desire to review more data, officials said they expected to provide that information within days. From their comments, however, it appeared officials were leaning against a fifth Test.

A handful of technical issues arose during Monday’s test, the biggest of which was a hydrogen leak in a quick disconnect at the bottom of the mobile launch tower that supports the SLS rocket during refueling. This 4-inch hydrogen line is one of many that are released from the rocket just before liftoff and are connected to the tower’s tail service mast.

NASA was unable to fix the problem with a leaky seal during the final part of Monday’s test, so instead opted to mask the leak from the ground launch sequencer, the ground computer which controls the majority of the countdown. This posed no risk to the rocket during the test, but needed to be corrected before an actual launch.

With that 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 full. When the ground launch sequencer was transferred to the rocket’s onboard computer for the last 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 on both the core and upper stage,” Blackwell-Thompson said. “The terminal count is a very dynamic period. I expected that we would need to talk about a couple of things in the terminal count, but it went extremely smoothly. There was nothing to say.”

This refueling test is the last major 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 if another wet wear test is needed. But Mike Sarafin, the Artemis I mission manager, said he believes NASA has achieved about 90% of the test goals so far.

In addition to fixing the leaking hydrogen seal, NASA still has to taxi the rocket to the vehicle assembly building to install and arm the flight termination system. This work probably prevents a launch attempt before the end of September at the earliest.

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