— NASA's second attempt at launching its first new "mega moon rocket" in 50 years ended in a scrub on Saturday (Sept. 3), after engineers were unable to correct for a liquid hydrogen leak. Mission managers have made the decision to forego trying again this upcoming week and instead are standing down to give time for engineers to understand and repair the leak.

Artemis I launch director Charlie Blackwell-Thompson called off the launch at 11:17 a.m. EDT (1517 GMT) with two hours, 28 minutes and 53 seconds left in the countdown. The Space Launch System (SLS) rocket had been scheduled to lift off with NASA's uncrewed Orion spacecraft at 2:17 p.m. EDT (1817 GMT) from Pad 39B at the Kennedy Space Center in Florida.

"This is part of the space business," said Bill Nelson, NASA's Administrator, in an interview with launch commentator Derrol Nail. "This is part of our space program. Be ready for the scrubs."

The liquid hydrogen leak first presented itself at 7:15 a.m. EDT (1115 GMT), soon after launch controllers began the flow of cryogenic liquid hydrogen into the SLS's core stage. Sensors picked up a rising concentration of hydrogen in the cavity between the ground and flight-side plates of a quick disconnect umbilical located in the SLS's engine compartment. The loading of hydrogen was automatically cut off when the leak concentration reached the point to be a flammability risk.

Based on past experience with similar quick disconnects, engineers twice tried to give time for the hardware to warm up and then resumed the fill of liquid hydrogen, hoping that the temperature shock from the super-chilled propellant would reseat the connection, forming a tight seal.

The team also tried pressurizing the cavity with helium, attempting to force a seal, but that also did not work.

Loading of liquid oxygen proceeded without issue and had reached its replenish mode before the scrub was called.

Saturday's leak was unrelated to a hydrogen leak during the first launch attempt on Monday (Aug. 29). The earlier issue had been in a tail service mast umbilical and was repaired in the days leading up to Saturday's attempt.

NASA's Artemis mission management team met Saturday afternoon to determine the next steps going forward. Access to the engine compartment is limited on the launchpad and, as of now, the vehicle must return to its assembly building so that its flight termination system batteries can be serviced.

Engineers believe the problem is with the soft goods inside the quick disconnect and are debating between removing and replacing those seals and other materials on the launchpad, where they can test their repairs under the same conditions as during a launch, or first returning to the Vehicle Assembly Building (VAB).

"There's a risk versus risk trade," said Mike Sarafin, Artemis mission manager, during a post-scrub press conference. "Doing it at the pad, you are exposed to the environmental conditions and you need to build an environmental enclosure. If we do it in the Vehicle Assembly Building, the assembly building is the environmental enclosure, however, we cannot test this quick disconnect in the VAB at cryogenic temperatures."

"So we're working through those options," said Sarafin.

That decision and the subsequent outcome of the repairs will affect when it is that NASA is ready to attempt the Artemis I launch again.

"If they [have to roll back, the next launch attempt] will be in October," said Nelson. "Although the window opens early [in the month], I suspect it will be more towards the middle because in the first week of October, we've got another crew ... that are going to the International Space Station."

More than ten years in development, Artemis I is the first integrated test of the SLS and Orion spacecraft. When it launches, the mission will send the uncrewed capsule on a distant orbit around the moon, traveling farther into space than any spacecraft built for astronauts has gone before.

The Orion's safe return to Earth will clear the way for future Artemis missions to fly astronauts into lunar orbit and return Americans to the lunar surface.

collectSPACE is grateful to film and TV company Haviland Digital for supporting our Artemis I coverage. Their team has produced and supported titles such as the award-winning "Last Man on the Moon," "Mission Control: The Unsung Heroes of Apollo" and "Armstrong."