Unable to tame hydrogen leaks, NASA delays launch of Artemis II until March

Because of this, NASA engineers acknowledge that a small amount of hydrogen will escape from the seal in the refueling line. Agency officials said in 2022 that the safe limit was a 4 percent concentration of hydrogen gas in the housing around the fuel connector. Hydrogen levels exceeded NASA’s safety limits several times during the practice countdown, which ran from Monday to early Tuesday.

“Efforts to resolve this issue include stopping the flow of liquid hydrogen to the core stage, allowing the interface to warm enough to re-establish the seal, and adjusting the flow of propellant,” NASA said in a statement.

NASA appeared to overcome the problem Monday evening and fully loaded the 322-foot-tall (98 meters) rocket with more than 750,000 gallons of propellant.

With refueling complete, managers sent a close crew to the launch pad around 6:00 p.m. EST (23:00 UTC) to close the hatch for the Orion spacecraft sitting atop the SLS rocket. The closeout team will help the Artemis II astronauts into the Orion capsule on launch day, but the crew was not part of the practice countdown Monday night.

It took longer than anticipated for the closeout crew to close and secure the Orion spacecraft’s hatch. According to NASA, a valve connected to Orion’s hatch pressure inadvertently popped out, requiring the closeout crew to retighten the valve. The launch team dealt with several other glitches, including audio dropouts on the ground communications loop and camera problems caused by recent cold weather in Central Florida.

Ultimately, with the closeout crew at a safe distance from the rocket, the launch team gave the go-ahead to begin the final 10 minutes of the countdown shortly after midnight Tuesday. Its purpose was to stop the countdown clock 33 seconds before launch, approximately the same time the rocket would take control of the countdown during the actual launch attempt.