NASA scrubs second try to launch moon rocket due to persistent hydrogen leak

NASA called off today’s attempt to launch its Space Launch System rocket due to a hydrogen leak encountered during the process of fueling up the core stage.

Mission managers said they’d have to pass up the current opportunity for liftoff, and although a firm decision hasn’t yet been made, it seems likely that the next launch attempt will have to wait until October.

NASA’s uncrewed test mission, known as Artemis 1, is meant to blaze a trail for sending astronauts to the moon.

“We’ll go when it’s ready,” NASA Administrator Bill Nelson said. “We don’t go until then, and especially now, on a test flight, because we’re going to stress this and test it … and make sure it’s right before we put four humans up on the top of it. So, this is part of the space business.”

Today’s scrub at Kennedy Space Center in Florida came five days after an initial postponement, which was attributed to concerns about the procedure for cooling down the SLS’s rocket engines prior to launch. Engineers suspected the problem was due to a bad sensor, and changed their procedures to deal with that scenario. However, today’s countdown didn’t get far enough to use those procedures.

This time around, the issue had to do with the fuel line that NASA uses to fill up the SLS’s tank with super-cooled liquid hydrogen propellant. Engineers detected a persistent leak in the connection between the fuel line and the rocket, and tried three times to reseat a seal in the connection.

“Unfortunately, attempts to troubleshoot it did not succeed,” NASA launch commentator Derrol Nail said.

The rocket’s liquid oxygen tank was fully filled, but Nail said the liquid hydrogen tank was only 11% filled when the countdown was called off at 11:17 a.m. ET (8:17 a.m. PT) — exactly three hours before the scheduled launch time.

During a post-scrub news briefing, Artemis mission manager Mike Sarafin said a valve was mistakenly opened in advance of today’s propellant loading process — which resulted in hydrogen pressure rising beyond the standard limit of 20 pounds per square inch to as high as 60 psi. He cautioned, however, that mission managers have not yet linked that inadvertent overpressure to the hydrogen leak.

Sarafin said the leak resulted in a concentration of hydrogen in ambient air that was two to three times higher than the 4% that NASA considers a safe level. “This was not a manageable leak,” he said.

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