Following their historic lunar flyby, the Artemis II crew is nearing the end of their 10-day mission, which will conclude Friday with the most intense phase of any astronaut’s journey: reentry into Earth’s atmosphere, followed by splashdown.

This is the critical moment where the spacecraft proves it can safely carry its crew back home. But when reentry begins, the world will need to wait about six minutes for that proof — the length of time that Mission Control will lose communication with the Artemis II crew.

Watch live coverage as the Artemis II crew returns to Earth beginning at 7 p.m. ET on ABC News Live, Disney+ and Hulu with special coverage beginning at 7:30 p.m ET on ABC. 

Unlike the 40-minute loss of communications experienced when the Orion crew module passed behind the moon, which physically blocked radio signals from reaching the spacecraft, loss of communication during reentry results from Orion’s passage through Earth’s atmosphere.

What happens when reentry begins

Orion will be falling to Earth at over 24,000 mph when it encounters the atmosphere. As the atmosphere thickens, friction will slow the spacecraft. It will also create a lot of heat – up to 5,000 degrees Fahrenheit, which is more than twice as hot as lava from a volcano – turning Orion into a fireball.

It will take Orion about 13 minutes to travel the 400,000 feet from space to splashdown off the coast of San Diego, Calif.

“Everything’s different,” retired NASA astronaut Barry “Butch” Wilmore told ABC News. “The speeds are much, much greater coming back from deep space.”

Together, the friction and compression of the atmosphere as Orion falls creates a plasma bubble that will engulf the spacecraft, according to NASA. It’s that engulfing plasma that doesn’t allow radio signals in or out.

Within seconds, the Artemis II crew will lose communication with ground controllers as what NASA calls a “planned six-minute blackout period” begins. 

What’s happening inside Orion?

“You know the blackout’s coming,” said Wilmore, who experienced reentry from space three times during his time as an astronaut. “Because of that, you just go press through just like your normal processes, you’re monitoring. There’s not a lot you can do.”

Everyone inside the spacecraft is laser-focused on monitoring the onboard systems during their descent through the atmosphere, according to Wilmore, who added that astronauts train for “all types of failures,” so their mindset is just to concentrate on the jobs at hand.

“You can’t let apprehension involve you in those time frames,” Wilmore told ABC News. “You have to focus on your task, whatever that might be, and you have to perform because if you don’t, the consequences are pretty dire.”

When the signal steps out, the heat shield steps in

Those six minutes of radio silence are also when Orion’s heat shield, located on the underside of the spacecraft, does its most critical work, protecting Orion and its crew from the intense temperatures of reentry. Onboard maneuvering jets ensure Orion maintains the orientation required to keep the heat shield pointed toward Earth during reentry.

After Orion completes its passage through the outer atmosphere and emerges from its communications blackout, it will still be traveling too fast for it to survive the splashdown into the Pacific. That’s when a series of specially designed parachutes will deploy, slowing Orion’s speed to a far safer 20 mph at the time of splashdown.

Orion is scheduled for splashdown at 5:07 p.m. PT/8:07 p.m. ET Friday, April 10, at a site off the coast of San Diego.