NASA’s Artemis II moon mission is coming to an end. On Friday at approximately 8:07 P.M. EDT, its Orion capsule, named Integrity, is due to splash down into the Pacific Ocean off the coast of San Diego, Calif., delivering astronauts Reid Wiseman, Christina Koch, Victor Glover and Jeremy Hansen back to Earth. But before that, Integrity must endure a perilous journey through our atmosphere: reentry.
Reentry is hard. When an object falls from space into our planet’s atmosphere at hypersonic speed, it heats up and is engulfed in a fireball. This is caused mostly by compressed air in front of the object and atmospheric drag. It’s stressful: if the falling object is small or relatively fragile and doesn’t have protection from the heat, it typically breaks apart and burns up. In the case of crewed vehicles such as Orion, however, engineers carefully map out a reentry trajectory and build in protection such as heat shielding to minimize the risk of harm to both the spacecraft and the astronauts inside.
Integrity is projected to reenter Earth’s atmosphere on Friday at approximately 7:45 P.M., when it will be traveling at nearly 24,000 miles an hour. Without a protective layer, anything inside the crew cabin could be exposed to temperatures as high as 5,000 degrees Fahrenheit.
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Like all Orion capsules, Integrity has a heat shield made of AVCOAT, a mixture of silica, epoxy and resins that NASA also used for the original Apollo missions to the moon. AVCOAT protects a spacecraft by charring, melting and ablating away, carrying excess heat along with it. Orion’s AVCOAT has been slightly reformulated, and the design of its heat shield is not the same as that of the Apollo missions: while in the past, the Apollo heat shields had a honeycomblike structure made up of 36,000 small cells of AVCOAT, the Orion heat shield is made up of less than 200 large tiles of the material.
Before Artemis II, an uncrewed Orion capsule flew in 2022 as part of the Artemis I mission, allowing a test of its heat shield without risking anyone’s well-being. During reentry, that heat shield cracked and shed more material than NASA engineers had expected. The space agency performed an urgent investigation into the anomaly and released a report detailing its findings in 2024. Ultimately, citing the expense and time any replacement would’ve taken, NASA decided not to change the heat shield design for Artemis II’s Orion capsule. Instead mission planners adjusted the capsule’s reentry trajectory so that its heat shield would be exposed to higher temperatures for a shorter time.
Orion’s heat shield has been extensively tested on the ground, and NASA officials have said that their models show the new reentry profile effectively minimizes the reentry risk for the Artemis II crew.
“I am confident in the NASA approach and solution,” says Jud Ready, a materials expert and executive director of the Space Research Institute at the Georgia Institute of Technology. “It was a rigorous study using ground-based experimentation at representative pressures, temperatures and—crucially—temperature ramp rates.”
But the decision to leave the heat shield as it was for Artemis I has been met with criticism by other heat shield experts and even former astronauts. “This approach doesn’t mitigate the flaws in the design and manufacture of the original heat shield itself,” says Ed Pope, a heat shield expert, who has been critical of NASA’s decision. He points out that the agency is using a different heat shield design and yet another formulation of AVCOAT for the Orion capsule on Artemis III. “That change is an acknowledgement that there's a known risk to the current design and manufacturing method, in my opinion,” he says.
After Integrity bleeds off most of its speed during reentry and is deeper in Earth’s atmosphere, it will use its thrusters and, eventually, parachutes to slow down, reaching a stately 17 miles an hour. The entire process should take about 13 minutes, according to Artemis II entry flight director Rick Henfling. There will be a several-minute-long period in which the spacecraft will lose communications with mission control as it passes through Earth’s upper atmosphere, says Jordan Bimm, a space historian at the University of Chicago.
“For me, this will be the most stressful part of the entire mission,” Bimm says.
Presuming a nominal reentry and an on-target splashdown, U.S. ships waiting nearby will retrieve the astronauts and bring the mission to its official close.
