The four astronauts on NASA's Artemis 2 mission prepared Sunday to enter the Moon's "sphere of influence," having already taking in sights of the lunar surface never before seen by human eyes.

As they awoke for day five of the 10-day mission, their Orion spaceship was nearly 215,000 miles (346,000 kilometers) from Earth and 65,000 miles from the Moon, according to NASA's online dashboard.

Former astronaut Charlie Duke, who walked on the Moon in 1972 as part of the Apollo 16 mission, gave the ceremonial wakeup call to the crew.

"Below you on the Moon is a photo of my family. I pray it reminds you that we in America and all of the world are cheering you on. Thanks to you and the whole team on the ground for building on our Apollo legacy with Artemis," said the 90-year-old.

Earlier, in the wee hours of Sunday, the US space agency published an image taken by the Artemis crew, showing a distant Moon with the Orientale basin visible.

"This mission marks the first time the entire basin has been seen with human eyes," NASA said. The massive crater, which resembles a bullseye, had been photographed before by orbiting cameras.

The next major milestone is expected overnight Sunday into Monday, at which point the astronauts will enter the "lunar sphere of influence," where the Moon's gravity will have stronger pull on the spacecraft than Earth's.

"We're all extremely excited for tomorrow," Lori Glaze, the deputy associate administrator for NASA's Exploration Systems Development Mission, told reporters Sunday. 

"Our flight operations team and our science team are ready for the first lunar flyby in more than 50 years."

For the period of the flyby, which will last for several hours, the Artemis 2 crew will observe the celestial body with their naked eyes, along with cameras they have on board. 

"I think it's important to remember that, you know, we don't always know exactly what they're going to see," Kelsey Young, the lead scientist for the Artemis 2 mission, told a press conference Sunday.

If all proceeds smoothly, as the Orion spacecraft whips around the Moon, the astronauts -- Americans Christina Koch, Reid Wiseman and Victor Glover along with Canadian Jeremy Hansen -- could set a record by venturing farther from Earth than any human before.

Systems tests

NASA said the Artemis crew has completed a manual piloting demonstration and reviewed their lunar flyby plan, including reviewing the surface features they must analyze and photograph during their time circling the Moon.

At the same time, "we're focusing very much on the ecosystem, the life support system of the spacecraft," NASA chief Jared Isaacman said Sunday in a televised interview with CNN.

"This is the first time astronauts have ever flown on this spacecraft before. That's what we're most interested in getting data from," he added.

On day five, the astronauts were testing their "survival" suits, according to NASA.

The bright orange suits are worn during takeoff and re-entry, but also emergency situations, such as cabin depressurization.

The crew "will conduct a full sequence of suit operations, including putting on and pressurizing their suits, performing leak checks, simulating seat entry, and assessing mobility and their ability to eat and drink," NASA said.

While the four astronauts will not touch down on the lunar surface, they are expected to break the record for the farthest distance from Earth during their pass around the Moon.

Over the next day, "they will be on the far side of the Moon, they will eclipse that record, and we're going to learn an awful lot about the spacecraft," said Isaacman.

The information will be "pretty paramount to set up for subsequent missions like Artemis 3 in 2027 and, of course, the lunar landing itself on Artemis 4 in 2028."