CAPE CANAVERAL, Florida — In the latest setback to return astronauts to the moon, NASA delayed the highly anticipated flight yet again after a new problem cropped up with the rocket on Saturday.

April is now the earliest that the four Artemis II astronauts could fly to the moon.

NASA revealed the latest problem just one day after targeting March 6 for Artemis II, humanity's first flight to the moon in more than half a century. Overnight, the flow of helium to the rocket's upper stage was interrupted, officials said. Solid helium flow is essential for purging the engines and pressurizing the fuel tanks.

This helium issue has nothing to do with the hydrogen fuel leaks that marred a countdown dress rehearsal of the Space Launch System rocket earlier this month and forced a repeat test.

NASA Administrator Jared Isaacman said a bad filter, valve or connection plate could be to blame for the stalled helium flow. Regardless of the cause, he said, the only way to access the area and fix the problem is to return the 98-meter rocket to its hangar for repairs.

"We will begin preparations for rollback, and this will take the March launch window out of consideration," Isaacman said via X. NASA's next opportunities would be at the beginning or end of April.

"I understand people are disappointed by this development," he added. "That disappointment is felt most by the team at NASA, who have been working tirelessly to prepare for this great endeavor."

Earlier in the day, NASA said it was preparing to move the rocket back to the Vehicle Assembly Building at Kennedy Space Center while raising the possibility of the work being done at the pad.

Hydrogen fuel leaks had already delayed the Artemis II lunar fly-around by a month. A second fueling test on Thursday revealed hardly any leaks, giving managers confidence to aim for a March liftoff.

Everything worked fine with the rocket's helium system during both dress rehearsals, Isaacman said. The "unexpected development" cropped up later in routine testing that kept engineers up all night assessing the situation.