NASA counts down within 29 seconds of the launch of the large SLS rocket

NASA attempted three times during the month of April to complete a critical fuel test of its massive rocket for the Space Launch System. And three times, due to about half a dozen technical problems, the space agency failed.

And so NASA made the difficult decision to return the massive rocket to the Vehicle Assembly Building for repair, adding two months of delay to a program already years behind schedule. After this work was completed in early June, NASA returned the SLS rocket and Orion spacecraft to the launch pad for a fourth attempt.

It turns out that the painful decision is the right one. Over the course of more than 14 hours Monday, NASA largely succeeded in completing this refueling test, carrying 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,” he said. Charlie Blackwell Thompson, Artemis launch director.

She and other NASA officials joined a conference call with reporters Tuesday to discuss the results of the fourth “rehearsal” test, which is intended to learn the kinks of the rocket’s countdown to launch day. To that extent, the test appears to have largely succeeded. NASA entered within T-29 seconds of take-off during the test, close to its intended target of T-9.3 seconds, before ending the test before igniting the rocket’s four main engines.

During the conference call, NASA officials declined to answer specific questions about whether a fifth test was needed — to reduce the count to T-9.3 seconds — or when the rocket would be ready for its first launch. Claiming to want to review more data, officials said they expect to provide that information within two more days. However, it appears from their comments that officials may be inclined to a fifth test.

A host of technical problems occurred during Monday’s test, the most significant of which was a hydrogen leak in a quick disconnect at the bottom of the moving launch tower supporting the SLS rocket while refueling. This 4-inch hydrogen line is one of several that are launched from the missile just prior to takeoff and are connected to the turret’s tail service mast.

NASA was unable to resolve the issue of a leaky leak during the final part of Monday’s testing, so instead chose to hide the leak from the ground sequencer, the computer on the ground side that controls the majority of the countdown. This did not pose any danger to the missile during testing but would have to be repaired before actual launch.

With that little bit of concealment, the NASA launch team was able to go from the T-10 to the T-29 minutes and demonstrate the ability to not only fill the SLS rocket but also maintain its fuel tanks. When the ground-launch regulator was handed over to the onboard computer of the rocket for the final part of the countdown, the flight computer automatically finished the count.

NASA officials liked what they saw. “This is the first time we’ve been in an extremely cold environment in both the primary and upper stage,” Blackwell Thompson said. “The final count is a very dynamic time. I was fully expecting that we might have a thing or two that we might need to talk about in the final count, but it was very smooth. There was nothing to talk about.”

The refueling test is the last major hurdle between the SLS rocket and its launch attempt later this year. There is still work to be done, and the agency must decide if a wet outfit test is necessary. But Mike Sarafin, Artemis I mission manager, said he believes that so far, NASA has completed about 90 percent of test goals.

In addition to fixing the leaking hydrogen seal, NASA still needs to return the rocket to the Vehicle Assembly Building to install and arm the flight termination system. This work will likely prevent a launch attempt before the end of September at the earliest.