The four Artemis II astronauts, returning from the world's first crewed moon voyage in over half a century, hurtled back toward Earth on Friday aboard their gumdrop-shaped Orion spacecraft, headed for a splashdown in the Pacific Ocean off Southern California.

The finale to NASA's celebrated 10-day mission was expected to begin with separation of Orion's crew capsule from its service module, followed by a fiery re-entry through Earth's atmosphere and a six-minute radio blackout before the capsule parachutes into the sea.

If all goes well, U.S. astronauts Reid Wiseman, Victor Glover and Christina Koch, along with Canadian astronaut Jeremy Hansen, will end up bobbing safely in the ocean aboard their Orion capsule, dubbed Integrity, shortly after 8 p.m. ET (0000 GMT) off the coast of San Diego.

The quartet blasted off from Cape Canaveral, Florida, on April 1, lofted into an initial Earth orbit by NASA's giant Space Launch System rocket before sailing on around the far side of the moon, venturing deeper into space than any humans before them.

In so doing, they became the first astronauts to fly in the vicinity of the moon since the Apollo program of the 1960s and '70s. Glover, Koch and Hansen also made history as the first Black astronaut, the first woman and first non-U.S. citizen, respectively, to take part in a lunar mission.

The voyage, following the uncrewed Artemis I test flight around the moon by the Orion spacecraft in 2022, marked a critical dress rehearsal for a planned attempt later this decade to land astronauts on the lunar surface for the first time since Apollo 17 in late 1972.

The ultimate goal of the Artemis program is to establish a long-term presence on the moon as a stepping stone to eventual human exploration of Mars.