NASA on Monday began the final countdown for humanity’s first crewed mission to the moon in more than half a century, marking a major milestone in the return to deep space exploration.

The 32-story Space Launch System rocket is poised to blast off Wednesday evening with four astronauts. After a day in orbit around Earth, their Orion capsule will propel them to the moon and back. There are no stops - just a quick U-turn around the moon. The nearly 10-day flight will end with a splashdown in the Pacific.

"Our team has worked extremely hard to get us to this moment,” said launch director Charlie Blackwell-Thompson. "Certainly all indications are right now we are in excellent, excellent shape.”

Managers said the rocket is doing well following the latest round of repairs. Forecasters said the weather should cooperate.

NASA’s Artemis II mission should have soared in February, but was grounded by hydrogen fuel leaks. The leaks were fixed, but then a helium pressurization line became clogged, forcing a return to the hangar late last month. The rocket returned to the pad 1 1/2 weeks ago, and its U.S.-Canadian crew arrived at the launch site on Friday.

Unlike Apollo, which sent only men to the moon from 1968 through 1972, Artemis’ debut crew includes a woman, person of color and a non-U.S. citizen.

Artemis II’s pilot Victor Glover said over the weekend that he wants young people to see them and think, "Girl power and that’s awesome, and that young brown boys and girls can look at me and go ‘Hey, he looks like me and he’s doing what???’”

At the same time, Glover, who is Black, looks forward to when ”one day we don’t have to talk about these firsts” and exploring the cosmos becomes an all-encompassing "human history.”

NASA has the first six days of April to launch Artemis II before standing down until the end of the month.