With Jackie Wattles, CNN
The Artemis II astronauts faced many dangers during their historic mission to the moon, including extreme stress during liftoff on April 1, when their rocket consumed millions of gallons of fuel, and the challenge of navigating dangerous radiation fields en route to the moon.
But perhaps the scariest milestone is yet to come: the return.
During this phase of flight, the astronauts’ spacecraft approaches the Earth at high speed and enters the dense inner layer of the Earth’s atmosphere, traveling at more than 30 times the speed of sound.
This process causes a strong compression of air molecules that can heat the outside of the capsule to more than 2,760 degrees Celsius.
“Honestly, I’ve been thinking about going back since April 3, 2023, when we were assigned to this mission,” Artemis II astronaut Victor Glover said of the milestone during a media event Wednesday.
“At one of the first press conferences, we were asked what we were most looking forward to, and I said: the fall. It’s a bit funny, but it’s also literal: we have to go back. You’ve already seen a lot of data, but the best is coming with us. There are many more photos, many more stories,” he commented.
Reentry is considered one of the most dangerous, if not the most dangerous, stages of any space flight. And the Artemis II mission will go through it with a known problem that is being monitored by mission controllers.
The problem came to light after Artemis I’s unmanned test flight around the moon in 2022, after which mission teams discovered that the capsule’s heat shield had returned with disturbing marks and cracks.
The heat shield is a critical component designed to protect the spacecraft and its astronauts from extreme temperatures during descent to Earth.
The Artemis I Orion spacecraft returned home safely, but the damage raised questions about how well engineers understood the material used to build the equipment, called Avcoat, and how it behaves during the dangerous and dynamic final phase of flight.
If the heat shield becomes damaged or cracked in some way, it can lead to catastrophic failure. And there is no escape mechanism that could save the astronauts at this point in the journey. If the heat shield fails, the mission and the crew will be lost.
The Orion spacecraft of the Artemis II mission has a heat shield almost identical to the heat shield of the Artemis I mission.
While NASA officials have acknowledged it’s not perfect, the agency says it can return the astronauts — NASA’s Reid Wiseman, Victor Glover and Christina Koch, and Jeremy Hansen of the Canadian Space Agency — safely, thanks to some changes to the mission’s reentry strategy.
Those in charge of the mission say they are confident they did a good job and understand the limitations of the heat shield and how to protect the crew, Amit Kshatriya, NASA’s deputy administrator, said during a news conference Thursday. And he added: “The crew will put their lives on the line.”
But he acknowledged that there was a lot at stake.
“The Orion spacecraft will enter Earth’s atmosphere at approximately 25,000 mph (40,000 km/h). This heat shield … will withstand the full force of reentry,” he explained. “Every system we’ve demonstrated over the past nine days — life support, navigation, propulsion, communications — hinges on the last few minutes of flight.”
Problems discovered during the Artemis I mission led to more than a year of research, analysis and ground testing as NASA tried to understand the unexpected behavior of the heat shield.
However, and this is very important, when Artemis I returned, the heat shield was already installed on the Artemis II capsule. This meant that it was too late to change the structure or design of the heat shield for this manned flight.
To solve the problem, NASA decided to place the capsule “Artemis II” and the astronauts on a different trajectory than the one that Artemis I followed to return home.
While the 2022 test flight used a jump in which the capsule dipped briefly into the atmosphere before regaining altitude and making a second descent, this trip will attempt a higher reentry, according to NASA flight director Rick Henfling.
The modified design is aimed at creating more favorable heating conditions in hopes of limiting, though not eliminating, cracking of the heat shield.
The research process gave NASA experts confidence that even if the heat shield did not work optimally, the astronauts would return home safely.
Howard Hu, director of NASA’s Orion program, echoed that view in an interview before the launch in late March. He also confirmed that the space agency will begin evaluating the performance of Artemis II’s heat shield immediately after its return.
After the Orion capsule is scheduled to touch down off the coast of San Diego while the astronauts are transferred by helicopter to a rescue ship, a diver will dive into the ocean to photograph the heat shield from below, giving those in charge of the mission some of the first evidence of its operation.
“It’s a faulty heat shield,” Dr. Danny Olivas, a former NASA astronaut who was part of an independent review team appointed by the space agency to investigate the incident, told CNN in January. “There’s no doubt that this is not the kind of heat shield that NASA would want to provide to its astronauts.”
Still, Olivas said he believes NASA “has the problem under control” after conducting a thorough investigation.
NASA’s decision drew criticism.
Dr. Charlie Camardo, a heat shield expert, scientist and former NASA astronaut who was also part of the first space shuttle crew to fly after the Columbia disaster in 2003, is among a group of former NASA employees who do not believe the space agency should have sent humans aboard the Artemis II lunar mission.
He was invited to a meeting at NASA headquarters in January to discuss the issue and review the agency’s research data. Camardo said he wasn’t convinced the agency understood how cracks in the heat shield could grow or cause a flight failure.
“The fact that we decided to send a crew on a vehicle with a defective heat shield is irresponsible, and I’m sure no Apollo explorer would have allowed that decision,” Camardo told CNN. “NASA has given up trying to develop an analytical solution that could help test all of the failure mechanisms of the ablative heat shield.”
During a conversation in late March, Camardo said he and other like-minded former NASA employees had sent letters to security officials expressing their concerns.
Signatories include Dan Ruskey, an advanced input systems and thermal materials expert who has worked for NASA for more than 30 years, and Edgar Zapata, a retired Kennedy Space Center engineer who still serves on NASA’s External Innovative Advanced Concepts Council (NIAC).
A security official responded by saying a committee called the Aerospace Security Advisory Group, or ASAP, would “take their concerns into consideration.”
Camardo emphasized that his opposition to Artemis II was not based on the belief that it would end in catastrophic failure. He believes that the mission will return safely.
As Camardo told CNN, his biggest fear is that the safe flight of Artemis II will serve as a way for NASA management to confirm the validity of their decision-making processes. And that, Camardo warned, would undoubtedly give the agency a false sense of security.
NASA has repeatedly emphasized that safety is its top priority.
In a statement to CNN in January, NASA said the agency “considered all aspects” in making decisions about the Artemis II heat shield, and noted that there are also “uncertainties related to the development and qualification of manufacturing process changes.”
Both senior officials of the Artemis II program and the astronauts expressed confidence that NASA understands the problem and that the capsule will return home safely.
“Researchers discovered the root cause, which was key” to understanding and solving the heat shield problem, Wiseman told reporters last July. “If we follow the new reentry trajectory planned by NASA, this heat shield will be safe to fly.”
Olivas, a former astronaut who participated in the study, also noted that “there is not a single flight that takes off without some doubt.”
“But NASA really understands what it has,” Olivas said. “They know the importance of the heat shield to the safety of the crew and I think they did a good job.”
Debbie Cort, deputy director of NASA’s Orion program, reiterated during a press conference Wednesday that the agency’s post-Artemis I tests gave her confidence in the plan to return the Artemis II astronauts home.
“We understand how the rest of the car behaves, and we’ve done an extensive ground test program to understand how that heat shield behaves,” Cort said.
As noted, NASA plans to use a modified return trajectory for this mission only.
On future flights, including the Artemis III flights, the Orion capsule will include updated heat shield materials designed to be more permeable, hopefully avoiding cracks.
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