The Artemis II mission officially entered its fifth and final day before the highly anticipated lunar flyby as the crew awoke Sunday to the CeeLo Green song "Work."

The astronauts also heard from Apollo 16 astronaut Charlie Duke, who once landed on the moon on a different kind of Orion — a lunar module bearing the same name.

"I'm glad to see a different kind of Orion helping return humans to the moon as America charts the course to the lunar surface," Duke said in his message to the four-person 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," Duke added. "Thanks to you and the whole team on the ground for building on our Apollo legacy with Artemis. Godspeed and safe travels home."

With the moon flyby just a day away, Sunday marks the final stretch of preparations before the big moment.

On Saturday, the crew received their full list of lunar targets, which includes 30 specific sites they’ll observe as they pass by the moon. During the observation period, the crew will go through a total of five shifts during what NASA is calling the lunar flyby sequence.

For the crew, the first four of those shifts are all about observing the lunar surface. This is when the windows will be pointing right at the moon. The astronauts will capture everything using their cameras and personal computers onboard the Orion crew module.

-ABC News' Briana Alvarado

Overnight, the Artemis II crew wrapped up a busy stretch of work in deep space, including a hands-on test of Orion's controls and more prep for Monday's lunar flyby.

According to NASA, the crew began a manual piloting demonstration at 9:09 p.m. ET, with mission specialists Christina Koch and Jeremy Hansen taking turns flying the spacecraft.

For about 41 minutes, they tested how Orion responds in different thruster modes to see how it handles both full, free movement and more limited steering. The goal is to give engineers a better sense of how the spacecraft performs when astronauts are actively flying it, NASA said.

NASA said the test is part of a series of evaluations, with commander Reid Wiseman and pilot Victor Glover expected to run a similar demonstration later in the mission -- on April 9 -- to give teams on the ground more data from different pilots.

Earlier in the day, the crew also spent time going over their plan for the lunar flyby. According to NASA, they reviewed a list of specific features on the moon's surface that scientists want them to photograph and describe.

That work will come into play on Monday, when Orion begins its flyby at 2:45 p.m. ET.

All of this is setting the stage for one of the most anticipated parts of the mission: when astronauts will see the moon up close and help document it in real time for scientists back on Earth.

The crew shared a new photo of the moon during day 4 of their mission, capturing parts of the lunar far side including Orientale basin peeking through from the right side of the lunar disk.

"This mission marks the first time the entire basin has been seen with human eyes," NASA said in an Instagram post.

-ABC News' Briana Alvarado

NASA leaders addressed a minor smell reported by the crew Saturday morning, prompting checks by the flight team.

"So we did actually look at our power data, our heater data," Orion deputy program manager, Debbie Korth said in a news conference. "Nothing looks anomalous."

She also added that a similar smell was reported on the ground, which could possibly point to a mechanical source.

“The teams are, looking at some data we have on the ground with that same similar type smell had been reported and think it might be more mechanical in nature, some tapes and some other materials that might be off casting, but really early in that investigation, so don't think there's any hazardous condition,” Korth said.

-ABC News' Briana Alvarado

NASA leaders confirmed Monday's lunar flyby will allow the crew to see parts of the moon humans have never seen before.

NASA's Science Mission Directorate lead Kelsey Young explained Saturday that parts of the lunar far side remain unfamiliar to human eyes because the Apollo missions were planned to launch when the near side was illuminated.

"So as they get closer, they'll be able to see features that human eyes have never before seen," Young at a news conference.

NASA's SLS (Space Launch System) Program John Honeycutt noted that even regions just imaged by robotic spacecraft are now visible to humans, referring to a photo taken from Orion on Friday.

The crew will also witness a solar eclipse during the mission lasting about 53 minutes, occurring an hour after Earthrise. 

-ABC News' Briana Alvarado

The Artemis II crew spoke to reporters from aboard the Orion spacecraft as they near the end of their historic lunar mission.

Cmdr. Reid Wiseman described one of the mission's most powerful experiences: a tribute to his late wife, Carroll, when Hansen asked Mission Control for permission to name a lunar crater in her honor.

"That was kind of the pinnacle moment of the mission for me," Wiseman said. "That's where the four of us were the most forged, the most bonded."

The moment, he added, left the entire crew in tears and strengthened their connection as a team.

Pilot Victor Glover said the mission reaffirmed his long-held belief about Earth's fragility.

"It doesn't change it -- it absolutely reaffirms that we live on a fragile planet in the vacuum of space," he said. "It's almost like seeing living proof."

Despite witnessing the moon up close, he said the experience reinforced humanity's shared responsibility to "find joy and lifting each other up."

Mission specialist Christina Koch described life inside the spacecraft as both cramped and surprisingly fluid.

"Yes, it feels bigger in microgravity and yes, we are bumping into each other 100% of the time," she said, noting that even simple tasks become team efforts.

-ABC News' Jason Volack