The four astronauts aboard NASA’s Artemis II mission are nearing their return to Earth, but a crucial and perilous phase of the mission remains ahead.

NASA astronauts Reed Wiseman, Christina Koch, Victor Glover, and Canadian astronaut Jeremy Hansen are set to return to Earth Friday night following a 10-day mission in space.

Their Orion capsule is scheduled to re-enter the atmosphere around 7:53 p.m. ET, embarking on a critical journey expected to take under 15 minutes. If everything goes as planned, the mission will conclude with a splashdown in the Pacific Ocean off San Diego’s coast at 8:07 p.m. ET.

“There’s a 13-minute window where everything must go right,” stated Jeff Radigan, NASA’s Artemis II flight director, at a recent press conference.

Reentry poses significant risks during spaceflight, exposing the craft to temperatures near 5,000 degrees Fahrenheit as it plunges through the atmosphere. This risk is heightened for Artemis II due to a known design flaw in the Orion spacecraft’s heat shield, crucial for shielding astronauts from extreme heat.

This marks the first crewed mission for the Orion capsule.

After the uncrewed Artemis I mission in 2022, NASA detected unexpected damage to the spacecraft’s heat shield.

NASA’s research revealed that certain materials in the heat shield cracked upon atmospheric reentry, leading to “charred material flaking off” in various areas. An investigation found that improper gas venting within the heat shield’s outer layers created pressure buildup, resulting in the damage.

As a result of these findings, NASA intends to revise the heat shield design for subsequent Artemis missions. The Orion spacecraft for future flights will feature a more permeable outer material layer. Unfortunately, by the time NASA identified the damage from Artemis I, the Artemis II capsule was already built and assembled.

Rather than redesign the heat shield, NASA adjusted the capsule’s reentry trajectory to mitigate risks for the astronauts. The Orion spacecraft typically descends into the atmosphere, “skipping” like a stone on water to lessen thermal stress and gravitational forces before its final descent. NASA Deputy Administrator Amit Kshatriya explained that this “skip” will be brief, allowing the capsule to descend more rapidly and at a steeper angle, thereby reducing exposure to extreme temperatures.

“All systems demonstrated over the past nine days, including life support, navigation, propulsion, and communications, hinge on the flight’s final moments,” stated Kshatriya during a Thursday media briefing.

He further expressed “high confidence” in the spacecraft’s heat shield with the optimized flight path.

Nonetheless, substantial risks remain, with the lives of four astronauts at stake.

Former NASA astronaut Charlie Camarda voiced concerns regarding the heat shield, suggesting NASA should have delayed the Artemis II launch pending further assessment of the existing design.

“History shows that incidents occur when organizations misjudge the complexities of problems. This issue mirrors patterns seen prior to previous tragedies,” he articulated in an open letter to NASA Administrator Jared Isaacman in January.

Conversely, Isaacman declared earlier this month that he holds “full confidence” in the performance of Orion’s heat shield.

Wiseman conveyed satisfaction with the current plan.

“If we adhere to the newly-established atmospheric entry path, this heat shield is safe for flight,” he affirmed during a pre-flight media event in July.

Radigan noted that precise orbital positioning is essential for the atmospheric reentry protocol. Mission control has dedicated significant effort over the past day and a half to maintain the Orion spacecraft’s orbital path, executing necessary engine burns.

“Avoid actions that are impossible,” Radigan emphasized. “Hitting the required angle is crucial for successful atmospheric reentry.”

During reentry, the Orion capsule is projected to achieve speeds nearing 24,000 miles per hour, with astronauts experiencing gravitational forces approximately 3.9 times that of Earth.

As the capsule penetrates the atmosphere, communication blackouts are anticipated due to plasma buildup surrounding the craft. Flight director Rick Henfling announced that this disruption is expected to last around six minutes.

“Post-blackout, Orion will be at approximately 150,000 feet, still descending rapidly,” he noted.

At approximately 6,000 feet altitude, the capsule will deploy three main parachutes to decelerate to about 20 miles per hour before making contact with the ocean.

The U.S. Navy is set to assist with recovery operations in the Pacific. Following confirmation of a safe landing area, NASA plans to extract Koch from the capsule first, followed in order by Glover, Hansen, and Wiseman.

At a press conference on Thursday, Kshatriya commended the crew, emphasizing it was time for flight officials, engineers, and recovery teams to bring them home.

“The crew has performed their duties,” he stated. “Now it’s our turn to execute our part.”