NASA’s Artemis II crew is expected to splash down Friday evening

More than a week after launching on the farthest journey humans have ever taken, the crew of NASA’s Artemis II mission is en route to splash back to Earth on Friday evening.

The high-speed, high-stakes descent, expected to conclude around 8:07 p.m. Eastern, will provide a crucial test of the Orion crew module, which must endure blistering temperatures and crushing pressures to carry its passengers safely through the atmosphere.

All eyes are likely to be on the spacecraft’s protective heat shield, which suffered damage during the uncrewed Artemis I voyage in 2022. This time around, NASA plans to forgo the maneuver that caused problems on the previous mission. Orion deputy program manager Debbie Korth also reassured reporters Wednesday that the agency had conducted a full visual inspection of the spacecraft using cameras on its exterior.

“Everything looks really good for the return,” Korth said.

Artemis II is an early step of an ambitious program to eventually return people to the moon’s surface and push deeper into the solar system. Over two weeks, NASA tested many of the components needed for an eventual lunar landing, including the first-ever crewed launch of the Orion module and a record-breaking flyby around the moon.

But reentry is one of the most intense phases of any mission, said engineer Marcos Fernandez-Tous, a specialist in space propulsion at the University of North Dakota, because astronauts have very little control over their plunge back to the surface.

Instead, the Artemis II crew must orient their spacecraft to enter Earth’s atmosphere at just the right angle, then surrender themselves to gravity for 10 stomach-churning minutes.

In that time, the Orion will be traveling as fast as 34,965 feet per second, and the astronauts will be subjected to forces almost four times the strength of Earth’s gravity, according to NASA entry flight director Rick Henfling. A cloud of extremely hot gas will surround the spacecraft, cutting off communication between the astronauts and mission control.

Finally, if all goes to plan, a series of parachutes will deploy to slow their free fall, allowing them to drop gently into the Pacific Ocean near San Diego.

NASA astronaut Doug Wheelock, who returned from the International Space Station aboard a Russian Soyuz spacecraft in 2015, likened the experience to “going over Niagara Falls in a barrel, but the barrel is on fire.”

For the Artemis II crew - pilot Victor Glover, commander Reid Wiseman and mission specialists Jeremy Hansen and Christina Koch - the reentry process will begin about five hours before touchdown, when they will perform a small engine burn to fine-tune their flight path.

If they enter Earth’s atmosphere at too steep an angle, Fernandez-Tous said, the friction of the atmosphere could create more stress than the spacecraft is able to tolerate. But if their approach is too shallow, the spacecraft may bounce off the edge of the atmosphere, like a rock skipping across the surface of a lake.

Sometimes such skips are intentional; in the 2022 Artemis I test, NASA used the maneuver to give itself more control over the spacecraft’s eventual landing site. But dipping in and out of the atmosphere caused gases to build up inside the heat shield, leading to cracks. Charred fragments of the shield’s outer layer were ripped away, making the shield less effective.

Monitors showed that temperatures inside the Orion module remained normal, NASA said, meaning if there had been astronauts aboard, they would have been safe.

But on this mission, the Artemis II will adopt a more direct approach. After their flight path is finalized, the crew will change into their launch and entry suits and jettison their service module, which provided power, water and air during their 10-day journey. Then, roughly 400,000 feet above Earth’s surface, it will enter the atmosphere.

“That’s when the fun really begins,” Henfling said Wednesday.

As the Orion module whooshes through the atmosphere, it encounters something that doesn’t exist in the airless void of space: friction.

That force begins to slow the spacecraft and turns its kinetic energy into heat.

Just 24 seconds after entry, the air around the craft will be so hot it turns to plasma - an electrically conductive superheated gas. Radio waves can’t travel through this material, leaving the astronauts completely cut off from the outside world.

In his memoir of the Apollo 13 mission, chief flight director Gene Kranz recalled how he offered a prayer for the crew during this period.

“Blackout was an eternity,” he wrote. “All eyes turned with a thousand-yard stare to the wall clocks as they counted down the final few seconds.”

But the Artemis II crew will really only be out of communication for six minutes, Henfling said. By the time they reemerge from their silence, they will be 150,000 feet above the Earth less than two dozen miles from their eventual landing site.

Next a series of parachutes will deploy, gradually slowing Orion to a leisurely 20 mph until it splashes into the Pacific.

Off the coast of San Diego, the USS John P. Murtha is already positioned to retrieve the astronauts from their landing site. Divers will open the hatch and help the astronauts onto an inflatable raft, where helicopters can pick them up and bring them to the ship.

If all goes smoothly, “it can look like flying to the moon is easy,” said Lakiesha Hawkins, acting deputy associate administrator for NASA’s Exploration Systems Development Mission Directorate.

She adjusted her glasses and looked out at her audience. “It certainly is not.”