아르테미스 II 우주비행사들이 역사적인 달 임무를 마치고 지구로 귀환

The four astronauts are heading back to Earth following their historic trip around the moon.

When four astronauts set off on their historic trip around the moon in NASA's 16.5-foot-wide Orion spacecraft, they knew they'd be testing a known flaw with their spacecraft - one that had some experts urging the space agency not to fly the mission with humans on board. NASA remains confident it has a handle on the problem and the vehicle can bring the crew home safely.

The issue relates to a special coating applied to the bottom part of the spacecraft, called the heat shield. It's a crucial piece of hardware designed to protect the astronauts from extreme temperatures as they're descending back to Earth during the final stretch of their moon-bound mission called Artemis II.

This vital part of the Orion spacecraft is nearly identical to the heat shield flown on Artemis I, an uncrewed 2022 test flight. That prior mission's Orion vehicle returned from space with a heat shield pockmarked by unexpected damage - prompting NASA to investigate the issue.

And while NASA cleared the heat shield for flight ahead of the April 1 launch, even those who believe the mission is safe acknowledge there is unknown risk involved.

"This is a deviant heat shield," said Dr. Danny Olivas, a former NASA astronaut who served on a space agency-appointed independent review team that investigated the incident, in a January interview. "There's no doubt about it: This is not the heat shield that NASA would want to give its astronauts."

Still, Olivas said he believes after spending years analyzing what went wrong with the heat shield, NASA "has its arms around the problem."

Artemis II crew members Mission Specialist Christina Koch (L), Mission Specialist Jeremy Hansen (top), Commander Reid Wiseman (R), and Pilot Victor Glover (bottom)
Photo: AFP/ HANDOUT - NASA

Upon completing the investigation about a year ago, NASA determined it would fly the Artemis II Orion capsule as is, believing it could ensure the crew's safety by slightly altering the mission's flight path.

In a statement to CNN in January, NASA said the agency "considered all aspects" when making that decision, noting there is also "uncertainty that comes with the development and qualification of the processes of changing the manufacturing process of the Avcoat ablator blocks."

Basically, NASA said, there's uncertainty involved no matter which course of action it takes.

"I think in my mind, there's no flight that ever takes off where you don't have a lingering doubt," Olivas said. "But NASA really does understand what they have. They know the importance of the heat shield to crew safety, and I do believe that they've done the job."

Lakiesha Hawkins, the acting deputy associate administrator for NASA's Exploration Systems Development Mission Directorate, echoed that sentiment in September, saying, "from a risk perspective, we feel very confident."

And Reid Wiseman, the astronaut set to command the Artemis II mission, has expressed his confidence.

"The investigators discovered the root cause, which was the key" to understanding and solving the heat shield issue, Wiseman told reporters last July. "If we stick to the new reentry path that NASA has planned, then this heat shield will be safe to fly."

Others aren't so sure.

"What they're talking about doing is crazy," said Dr Charlie Camarda, a heat shield expert, research scientist and former NASA astronaut.

Camarda - who was also a member of the first space shuttle crew to launch after the 2003 Columbia disaster - is among a group of former NASA employees who do not believe that the space agency should put astronauts on board the upcoming lunar excursion. He said he spent months trying to get agency leadership to heed his warnings to no avail.

"We could have solved this problem way back when," Camarda, who worked as a NASA research scientist for two decades before becoming an astronaut, said of the heat shield issue. "Instead, they keep kicking the can down the road."

The Artemis II crewed lunar mission lifts off from Pad 39B at Kennedy Space Center in Cape Canaveral, Florida, on April 1.
Photo: JIM WATSON / AFP

The Space Launch System rocket launched with the Orion spacecraft stacked on top - carrying NASA's Wiseman, Victor Glover and Christina Koch, and the Canadian Space Agency's Jeremy Hansen, on board - following final preflight safety reviews. The decision to launch was unanimous across mission managers, NASA officials said.

Even before Artemis, the Orion capsule - a US$20.4 billion spacecraft that NASA spent 20 years developing - was not exactly a darling of the aerospace community. Resentment for the vehicle has been brewing in various pockets of the industry for some time.

One engineer and physicist who previously worked on advanced technology development but did not work directly on the Artemis program derided Orion as "flaming garbage". A former employee at NASA's Jet Propulsion Laboratory, he decried the capsule's exceptionally long development timeline and cost overruns that have ballooned into the billions of dollars.

Lori Garver, a former deputy administrator for NASA under the Obama administration, has publicly lamented the politicking that colored the vehicle's path to completion.

But Orion's issues can't be fully pinned on politics, said Dr Ed Pope, a heat shield and material science expert who founded Matech, a California-based missile defense technology company. Pope did not participate in NASA's heat shield investigation.

"It's not a Republican thing or a Democrat thing at all," Pope told CNN. "It's a bureaucrat thing."

The decisions that led up to the heat shield issues NASA is grappling with today began early in the spacecraft's development process, according to Pope.

Orion program managers chose to make the spacecraft's heat shield out of Avcoat material in 2009. The heat shields manufactured for NASA's Apollo capsules all had a protective Avcoat layer, so leaders viewed it as a well-understood material with decades of data to back up its effectiveness.

For an uncrewed test flight in 2014, called EFT-1, the mission team outfitted an Orion capsule with a heat shield applied in the same manner as in the Apollo era - in an intricate honeycomb-like structure.

But that approach required a tedious manufacturing process that NASA hoped to avoid.

A camera on the tip of one of Orion's solar arrays captures the spacecraft
Photo: CNN / NASA

"It was very finicky, and it was going to be really, really hard to reproduce that quickly," said Pam Melroy, a longtime NASA employee, former astronaut and Air Force officer who once served as deputy administrator of the space agency. "That was part of the reason why we said, 'Let's just make this a simpler design.' It was really all about producibility."

Even before the EFT-1 test flight launched, NASA program managers wanted to alter the design, according to Melroy. Though NASA said in a statement the final decision was made in 2015.

NASA also said the honeycomb-structured Avcoat experienced issues during manufacturing for EFT-1, noting "cracks in seams appeared between the different honeycomb sections" and the material did not cure evenly and was weaker than expected. That made it "marginally acceptable" for the 2014 test flight and likely unusable for a lunar mission that requires far faster speeds and a more violent reentry process.

Textron Systems, the Texas-based company that produces Avcoat, told CNN in a statement that in 2015 it "licensed the Avcoat material to Lockheed Martin, who is contracted by NASA to manufacture the heat shields for the Artemis program" and deferred further comment to the aerospace giant.

Blaine Brown, director of Orion Spacecraft Mechanical Systems at Lockheed Martin Space, confirmed in a statement to CNN that the Avcoat structure was altered "to increase manufacturing and installation efficiency."

"We support NASA's decision to fly the Artemis II mission with its current heat shield and are committed to seeing Orion safely launch and return on its historic mission to the Moon with crew onboard," Brown said.

The Orion capsules built for the Artemis missions abandoned the Avcoat honeycomb structure in favor of a heat shield constructed using large blocks of the material.

"Our experience with a block design on Mars heat shields showed us that blocks were easier to produce, test and install," Brown said.

The first real-world test of the new Orion heat shield design, however, came with the Artemis I test flight in 2022. After that mission, NASA found chunks of the heat shield had broken off, leaving divots in the charred Avcoat material.

The Artemis II heat shield
Photo: NASA via CNN Newsource

That is not how the heat shield is supposed to behave. The Avcoat layer is meant to erode in an even, controlled manner as it heats.

NASA disclosed the problem months after Orion returned from space in 2022. The agency's office of the inspector general then released images of the ravaged Artemis I heat shield in a 2024 report.

Further complicating the situation was the fact that by that point it was already too late to fix the heat shield for Artemis II.

NASA did not - and could not - replace the Artemis II heat shield with a new one. The Orion capsule slated for the mission already had its heat shield installed even before Artemis I flew, and "you couldn't just go to Billy Bob's heat shield removal shop" to replace it, Olivas noted.

The investigation into the Artemis I heat shield issue also concluded that even though no astronauts were on board the test flight, "flight data showed that had crew been aboard, they would have been safe".

When asked about NASA's decision to move forward with the Artemis II mission without replacing the heat shield, Melroy, who oversaw the heat shield investigation as deputy administrator, said that NASA "program managers sometimes have to make these trades for cost, schedule and performance, and they certainly didn't undertake that decision lightly".

Heat shields produced for future Artemis missions will be manufactured with upgraded techniques, NASA leaders revealed in a December 2024 news conference.

Specifically, the agency plans to alter the "billet mold loading," essentially changing how much Avcoat is loaded into a mold to ultimately produce a more permeable shield, NASA said in its January statement to CNN.

In the meantime, analysis of what went wrong during the 2022 test flight is informing a new approach for Friday's anticipated splashdown off the coast of California.

The flags of the United States and Canada are seen on the left shoulder of the Orion Crew Survival System suits
Photo: Joel Kowsky/NASA via CNN Newsource

Avcoat is ablative, meaning the material is designed to char and erode in a controlled manner as the spacecraft comes roaring back from the moon and dips back into the thick inner band of Earth's atmosphere while still traveling more than 30 times the speed of sound.

This phase of flight, called "reentry", causes a violent compression of air molecules that can heat the spacecraft's exterior to more than 2760C.

NASA engineers designed the Orion spacecraft for a "skip reentry" - the capsule acts like a flat stone skipping atop the surface of a still lake as it dips briefly into the atmosphere and briefly raises its altitude once more before final descent. The special trajectory allows Orion to target a precise splashdown location.

In 2024, NASA twice opted to delay the timeline for the Artemis II launch in part to allow more time to collect data.

The problem, NASA concluded after months of research, was that the Avcoat material used in the Artemis I heat shield was not permeable enough. That meant that when the Orion capsule dipped into the atmosphere, gases built up in the heat shield's interior, causing chunks of the material to break off and cracks to form.

None of the experts interviewed by CNN dispute this characterisation of why the Artemis I heat shield did not perform as expected.

Up for debate is how well NASA's Artemis mission managers understand the problem and exactly how much risk the suboptimal heat shield poses to the four astronauts slated to launch in a few weeks.

In September, some of the space agency's Artemis program leaders said they believed Orion's heat shield would perform well on Artemis II, despite there being no substantial changes to its design.

In fact, while NASA now plans to manufacture future heat shields to be permeable, Artemis II's heat shield is actually less permeable than the one built for Artemis I.

About 6 percent of the Artemis I heat shield's surface area was permeable, Olivas noted, and that permeable area did not suffer any cracking. But the Artemis II heat shield, he added, does not have any permeable areas, noting that change was made prior to the Artemis I test flight and before NASA realized the heat shield needed to be permeable to perform well.

Rick Henfling, the Artemis flight director leading reentry, said during a September news conference that the Artemis II reentry trajectory has been modified with the goal of avoiding the conditions that caused the Artemis I heat shield to crack.

"We won't go as high on that skip, it'll just be a loft," Henfling said.

This new reentry path, Henfling said, should allow the Avcoat material to erode normally.

"We want to emphasize that safety is our top priority," Hawkins added, repeating a long-held NASA mantra.

The decision to use an altered trajectory was made after extensive testing, NASA said in its January statement. And the adjusted return path is designed to create "a steeper descent angle to reduce exposure time at peak heating, thus minimizing further char loss."

"This thorough testing, analysis, simulation, and expert validation collectively formed NASA's official flight rationale providing sufficient justification to proceed without redesigning the heat shield," the statement reads.

Other experts, however, disagree that changing Orion's flight path is enough to guarantee that the crew will make it home safely.

"The reason this is such a big deal is that when the heat shield is spalling - or you have big chunks coming off - even if the vehicle isn't destroyed, you're right at the point of incipient failure now," said Dr. Dan Rasky, an expert on advanced entry systems and thermal protection materials who worked at NASA for more than 30 years.

"It's like you're at the edge of the cliff on a foggy day," Rasky said.

Rasky, like Camarda, does not believe that NASA should allow astronauts to fly on board the Artemis II Orion capsule.

NASA's Artemis II Space Launch System rocket and Orion spacecraft are rolled out of the Vehicle Assembly Building to Launch Pad 39B
Photo: Miguel J. Rodriguez Carrillo / AFP

Even some experts who believe Artemis II is safe to fly acknowledge that the Orion heat shield will likely crack and display signs of damage upon its return from Earth, even with the modified trajectory.

"Will the heat shield crack? Yes, it's going to crack," Olivas, the astronaut who aided NASA's heat shield investigation, said.

But Orion has some built-in "robustness", said Dr Steve Scotti, a distinguished research associate at NASA's Langley Research Center in Hampton, Virginia, who served as a volunteer on an advisory team that was involved in the Artemis I heat shield investigation.

Underneath the Avcoat layer, Scotti said, lies a composite structure that during testing has been able to briefly survive the extreme temperatures of reentry. And that structure could serve as a last line of defense in the unlikely case that the Avcoat material becomes so deformed it begins to expose the underside of the spacecraft, Scotti said.

The composite structure wasn't put there as a fail-safe or backup for the heat shield - but it's lucky it is there, Scotti said.

Olivas emphasized that NASA isn't expecting to rely on the composite structure to keep the astronauts safe. The Avcoat material should still do that, he said. But the structure does provide an extra layer of safety, Olivas noted.

And even if the Artemis II heat shield performs worse than it did during Artemis I, Olivas and Scotti are confident the astronauts will remain safe.

"I don't have any strong fears that the crew is in danger," Scotti told CNN, echoing Olivas' sentiments.

But neither Scotti's nor Olivas' expressions of optimism come without an asterisk. Both experts acknowledge, as Camarda argues, that engineers cannot possibly predict exactly how the heat shield will behave.

"There's very little data to be able to put into an analysis" of the heat shield, Scotti told CNN. "The material itself changes every 20 seconds or so during reentry," he said, referring to the Avcoat layer.

"We still have things we don't know," Scotti added. "It's not low risk, it's a moderate risk."

Scotti's and Olivas' votes of confidence in the Artemis II mission were hard won.

Olivas, in fact, held serious doubts about NASA's intention to fly the Artemis II mission with crew until he sat through a three-hour meeting at the space agency's headquarters in Washington, DC, on 8 January.

CNN requested and was denied access to the meeting. Only two journalists were invited to attend, and the meeting was expected to be largely off the record because confidential information was being discussed.

NASA's newly installed administrator, Jared Isaacman, convened the meeting to gauge dissenting opinions, he told CNN affiliate station WESH in Orlando.

The meeting, Isaacman said, "only reaffirmed my confidence in the decisions of the bright engineers at NASA".

"We have modified our reentry profile. We have regained margin to safety, and I feel very good about that with Artemis II," he added.

Olivas said his hesitations were resolved by a presentation from a "Tiger Team" - a NASA term for a specialized team brought together to solve a complex problem - at Johnson Space Center in Houston.

"The key parameter here is: When is the heat shield going to crack? And how deep into the atmosphere are you going to be if it does crack?" Olivas said.

"There's things that we can never know until it actually happens," he added, referring to the heat shield. But the Tiger Team's analysis gave him confidence that NASA understood the Avcoat material well enough to be certain the crew would not be in danger.

"The Tiger Team did a phenomenal job," Olivas said. "I trust those engineers emphatically, and the program managers who are driving them."

That, however, is where Camarda - who also attended the 8 January meeting at NASA headquarters - disagrees.

Jeremy Hansen, Artemis II mission specialist, NASA astronauts Victor Glover, Artemis II pilot, Reid Wiseman, Artemis II commander, and Christina Koch, Artemis II mission specialist
Photo: JIM WATSON / AFP

Camarda takes issue, for example, with a computer program that the Tiger Team used in its heat shield analysis.

Called the Crack Indication Tool, or CIT, it was meant to model how and when the Avcoat material might begin fragmenting in various conditions.

What if Orion were to take a smaller "skip" before making its final plunge?

The CIT is meant to churn out data about how such changes might impact the heat shield - and whether those scenarios would trigger cracking.

But the data is imperfect, Camarda argues, and the tool relies on "simplifying assumptions".

"The analysis is a simplistic model to predict gas generation, material charring and qualitatively when cracks happen," Camarda said. "But the failure mechanism is how the cracks grow, and it definitely can't predict that. It cannot predict the stresses and strains that cause the cracks or how they can grow."

When asked about Camarda's criticisms of the CIT, Olivas acknowledged that no computer modeling program is completely accurate. And the CIT cannot predict crack growth.

But among the data points that assuaged Olivas' concerns, he said, was the fact that the Tiger Team lined up the computer program's predictions with real-world lab tests involving Avcoat material. The CIT was also able to correctly predict and re-create the conditions that led to the cracking on Artemis I.

"That gave me a confidence that the tool itself was indeed a good predictor," Olivas said.

But, Camarda counters, it is possible to create modeling tools that take a more interdisciplinary approach.

"A multi-physics analysis can do everything in one computer code," Camarda said. "It's predicting the aero thermodynamic heating on the outside of the vehicle, and studying how the material changes phases and starts to burn and produces gases."

That, he said, is the type of analysis that could give program managers a more holistic understanding of the risks this heat shield poses.

To Camarda, the heat shield problem is one symptom of a widespread ailment plaguing NASA that took root in the shuttle era. His view of the agency is informed by his experience as a young astronaut preparing to fly when the Space Shuttle Columbia broke apart during reentry in 2003, killing all seven passengers.

It marked the second tragedy for the program after the Space Shuttle Challenger was destroyed during ascent in 1986.

In a phone interview with CNN, Camarda highlighted that in the early 1980s, NASA had estimated that the space shuttle would have a roughly one in 100,000 chance of experiencing a deadly malfunction.

Ultimately, however, the shuttle flew a total of 135 missions with two explosions, resulting in 14 total casualties. That put the vehicle's actual odds of experiencing a catastrophic failure at 1 in 67.5.

At one point during his NASA career, Camarda was appointed head of engineering at Johnson Space Center only, he said, to be pushed out from that role after vocally expressing concerns about mission safety in the aftermath of the Columbia disaster, he wrote in "Mission Out of Control," a memoir and technical deep dive about his years at the agency.

Camarda's former boss did not respond to an email request for comment.

Camarda ultimately left NASA in 2019 after 45 years of service.

The first mission photo from the far side of the moon, captured from Orion as Earth dips beyond the lunar horizon.
Photo: NASA via CNN Newsource

In his view, the space agency has shifted away from a research and discovery mindset that it embodied during the Apollo era - when engineers were encouraged to identify and express concerns about potential safety issues as they picked apart engineering challenges on a fundamental level.

In today's climate, Camarda said, he worries NASA employees are encouraged to fall in line with the assessments and goals of the agency's management and leadership.

Edgar Zapata, a retired Kennedy Space Center engineer who still serves on the NASA Innovative Advanced Concepts (NIAC) External Council, a program that aims to fund bleeding-edge technology development, said he shares Camarda's concerns.

"I think our experiences are shaded by having seen that once this body politic decides, almost by mysterious forces, that it's going to do something - it tends to figure out a way to move forward," Zapata said of NASA's decision-making process and risk assessments.

NASA spokespeople did not respond to a request for comment about criticisms from Camarda regarding the agency's culture. NASA has long maintained and emphasized that it considers safety to be its top priority.

Camarda also emphasised that his opposition to Artemis II isn't driven by a belief it will end with a catastrophic failure. He thinks it's likely the mission will return home safely.

More than anything, Camarda told CNN, he fears that a safe flight for Artemis II will serve as validation for NASA leadership that its decision-making processes are sound. And that's bound to lull the agency into a false sense of security, Camarda warned.

The two former astronauts - Olivas and Camarda - do not share the same opinion about whether NASA should launch the Artemis II mission with crew on board. But on this point, they agree: "Sometimes we get lucky. And when we get lucky, sometimes we trade that for being good - and then we convince ourselves we're better than we really are," Olivas told CNN.

"I think it's valid to question what's happening at NASA," Olivas added, "because our history is not perfect."