After becoming the first humans in more than 50 years to fly around the moon, the four Artemis II astronauts face the final major challenge of their mission with their return to Earth.
"I've actually been thinking about entry since April 3, 2023, when we got assigned to this mission," US astronaut Victor Glover said when asked how he was feeling about the return during a press conference from the Orion capsule.
He described it as "riding a fireball through the atmosphere."
In a complex manoeuvre, the crew - made up of Glover, fellow US astronauts Christina Koch and Reid Wiseman as well as Canadian Jeremy Hansen - are due to splash down in the Pacific near San Diego at around 5:07 pm on Friday (0007 GMT Saturday).
At times, their capsule is expected to reach speeds of up to about 38,400 kilometres per hour, exposing the astronauts to extreme physical strain.
Orion is set to be exposed to intense heat as it re-enters Earth's atmosphere, with the astronauts protected by a special heat shield. Communications with mission control are due to drop out for around six minutes. The capsule is then expected to be slowed by parachutes before splashing down in the Pacific.
NASA said the latest weather forecasts and final exterior images of Orion looked good.
The four Artemis II astronauts were the first humans to travel near the moon in more than 50 years. They lifted off last week aboard the Orion capsule on NASA's Space Launch System rocket from Cape Canaveral in the US state of Florida before flying around the moon.
During the mission, they travelled farther from Earth than any humans before.
