Members of the crew can be seen in their orange spacesuits now while at the controls of the Orion spacecraft ahead of their reentry.

Here's a look at the "carefully timed sequence" of the final stages of Orion's descent, according to NASA. All times Eastern.

7:33 p.m.: Orion's crew module will separate from the European Service Module, exposing the heat shield that will protect the spacecraft as it travels through the Earth's atmosphere.

7:37 p.m.: Orion will perform an 18-second raise burn that fine-tunes the reentry angle of the spacecraft to minimize the time the heat shield will experience high temperatures.

7:53 p.m.: Orion will make first contact with the upper atmosphere, beginning a planned 6-minute communications blackout. The crew is expected to experience up to 3.9 Gs as the spacecraft travels nearly 35 times the speed of sound.

7:59 p.m.: NASA will regain communications with the crew.

8:03 p.m.: At around 22,000 feet in altitude, drogue parachutes will deploy to help slow the capsule ahead of splashdown.

8:04 p.m.: Three main parachutes will deploy at around 6,000 feet, reducing Orion's speed to less than 136 mph.

8:07 p.m.: Orion will splash down in the Pacific Ocean, off the coast of San Diego, having slowed to 20 mph.

The U.S. Geological Survey warned residents of Southern California that they should expect to hear a sonic boom from the Artemis II reentry in a few hours.

The sonic boom is expected between approximately 5-5:15 p.m. PT, it said.

It will take Orion about 14 minutes to travel the 400,000 feet from space to splashdown off the coast of San Diego.

Everyone inside the spacecraft will be laser-focused on monitoring the onboard systems during their descent through the atmosphere, according to retired NASA astronaut Barry "Butch" Wilmore.

The astronauts train for "all types of failures," so their mindset is just to concentrate on the jobs at hand, he said.

"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."

-ABC News' Briana Alvarado

The Artemis II moon mission will see four astronauts go on a 685,000-mile, 10-day journey around the moon. Here is what the timeline looks like:

Day 1 is launch day. The astronauts lift off aboard NASA's newest spacecraft, Orion, which will sit atop the Space Launch System rocket. The spacecraft will reach initial orbit and then high-Earth orbit to make a push toward the moon.

Days 2 through 4 are transit days, with the journey to the moon taking three days. Over the course of the journey, the crew will continue to evaluate Orion's systems and practice emergency procedures, in addition to other activities.

On day 5, Orion will enter the lunar sphere of influence, meaning the moon is the main gravitational pull. On day 6, the crew will come its closest to the moon while traveling the farthest from Earth, according NASA.

Days 7 through 10 will see the astronauts make their way back to Earth before re-entering Earth’s atmosphere at high speed, up to 25,000 miles per hour.

The Orion spacecraft will deploy a series of parachutes once through the heat of re-entry to slow down and it will splash down in the Pacific Ocean The U.S. Navy will recover the capsule.

-ABC News’ Mary Kekatos