There's an issue with the Artemis II heat shield, but NASA isn't worried. Here's why.

The Artemis II astronauts are about to return from a record-setting trip around the moon, but is their Orion spacecraft's heat shield safe to bring them home? NASA and the astronauts say yes, but not everyone agrees.

The Artemis II mission, which launched April 1, is set to end with a dramatic splashdown in the Pacific Ocean late Friday (April 10). NASA's first crewed flight to the moon since 1972 has led to some stunning images and poignant human moments. However, the reentry — which will occur at over 25,000 mph (40,000 km/h) to make the crew the fastest humans in history — will be the most dangerous hurdle yet.

That's because Artemis II's heat shield, which sits at the bottom of the Orion capsule and is designed to protect the crew as they hurtle through Earth's atmosphere, is almost exactly the same as the one used for Artemis I. And that heat shield cracked upon reentry.

"The capsule is going to approach temperatures on reentry of about half that of the surface of the sun," Ed Macaulay, a lecturer in physics and data science at Queen Mary University of London, told Live Science. "The heat shield is essential to protect the capsule from this scorching heat of reentry. Without it, the capsule would just completely melt and burn up."

The shield is made of a material called Avcoat, which is supposed to erode gradually upon reentry. However, NASA found that during Artemis II's predecessor, the uncrewed Artemis I mission in 2022, Orion's heat shield lost chunks of material, suffering much more than predicted.

To address this issue, NASA hasn't replaced the heat shield, however. Following an investigation, the agency concluded that it could ensure the safety of its crew by tweaking the flight path instead.

For Artemis II, Orion won't skip as high as its predecessor did on reentry; instead, it will make a little "loft" movement. The spacecraft will come in at a steeper angle and spend less time in the part of the atmosphere where the problems with Artemis I occurred.

NASA is confident this modification is sufficient to keep the astronauts safe. However, NASA Administrator Jared Isaacman has acknowledged that this approach "is not the right way to do things long term" and that there is no plan B.

"The heat shield has to work," Isaacman said in an interview shared by The Free Press on Tuesday (April 7). "I'm going to be thinking about that constantly until they're back in the water."

"I have no doubt the team did the right analysis on this," Isaacman added. "We altered the mission profile — the whole reentry profile is very different than Artemis I to account for what I would describe as the 'shortcomings' of the current heat shield on that vehicle."

It's important to note that Artemis I's heat shield didn't fail: there was plenty of Avcoat left, and data collected inside the capsule revealed that internal temperatures remained normal. If astronauts were aboard Artemis I, they would have been fine.

What happened to the Artemis I heat shield?

Some charring was expected as the Artemis I Orion capsule came racing down to Earth, reaching temperatures of around 5,000 degrees Fahrenheit (2,800 degrees Celsius).

However, when the uncrewed Orion capsule finally splashed down off the coast of Mexico on Dec. 11, 2022 — completing the hottest and fastest reentry ever — NASA immediately saw that the heat shield had lost chunks of material, suffering more than predicted.

"When the Artemis I capsule returned to Earth, it did make it safely through the atmosphere, but the damage and effects to the heat shield were more severe than had been anticipated from the modeling," Macaulay said.

So although the shield didn't fail, given this "char loss," it didn't pass with flying colors, either. In May 2024, NASA's Office of Inspector General released a report on NASA's readiness for Artemis II. The report found that the heat shield had worn away "differently than expected" in more than 100 areas, Live Science's sister site Space.com reported. At the time, the recommendations were for NASA to get to the root cause of the problem prior to the Artemis II launch.

But NASA had already committed to the heat shield for Artemis II. Technicians at NASA's Kennedy Space Center attached a heat shield to the Artemis II Orion spacecraft in July 2023, well before NASA had finished investigating the heat shield issues on Artemis I. NASA had delayed the Artemis II mission, in part to understand the issue with the heat shield, but the space agency couldn't stop working on Artemis II.

In December 2024, NASA pushed the Artemis II launch to 2026 and finally announced that it had identified the root cause of the Artemis I heat shield char loss: Essentially, the Avcoat material that's so vital to the heat shield's success couldn't "breathe."

"Engineers determined as Orion was returning from its uncrewed mission around the Moon, gases generated inside the heat shield's ablative outer material… were not able to vent and dissipate as expected," a NASA spokesperson wrote in a statement at the time. "This allowed pressure to build up and cracking to occur, causing some charred material to break off in several locations."

Tweaking the reentry

Part of the problem, it turned out, was the mission's unprecedented reentry.

For Artemis I, NASA performed a "skip" reentry, in which Orion bounced off Earth's atmosphere. The capsule skipped like a stone on a lake, dipping into the upper part of the atmosphere and then flying back out again, before reentering a second time. This strategy extended the range that Orion could fly between reentering the atmosphere and splashing into the Pacific Ocean, according to NASA. The idea was for the spacecraft to splash down closer to the U.S. and improve landing accuracy. A skip entry was also supposed to make reentry smoother for the astronauts.

As part of the heat-shield investigation, NASA replicated the Artemis I entry trajectory environment at NASA's Ames Research Center in California. Investigators found that thermal energy accumulated inside the Avcoat between dips. This caused pockets of gas to build inside the Avcoat faster than they could disperse, thereby creating pressure spikes that fractured parts of the material.

NASA had attempted to replicate the skip reentry on the ground prior to Artemis I, but the agency had tested at higher temperatures than Orion ultimately experienced. The heat shield's thermal performance had actually exceeded NASA's expectations, but it was the temperature drop that caused the problem.

"The less severe heating seen during the actual Artemis I reentry slowed down the process of char formation, while still creating gases in the char layer," the NASA spokesperson wrote. "Gas pressure built up to the point of cracking the Avcoat and releasing parts of the charred layer."

NASA found that in areas where the Avcoat was permeable, the heat shield didn't experience cracking or char loss — those parts of the heat shield could vent, so pressure didn't build up.

This isn't ideal news for Artemis II, which is using an even-less-permeable heat shield. (Around 6% of the Artemis I heat shield was permeable, whereas no areas of the Artemis II heat shield are permeable, CNN reported.) NASA made that change before the Artemis I test flight.

Why is NASA so confident?

After extensive testing and an independent review, NASA concluded that it had gotten to the bottom of the issue and that altering the reentry strategy would mitigate any risks. The Artemis II reentry won't replicate the temperature environment that NASA blames for Artemis I's heat shield problem.

Further assurance came in January 2026, when Isaacman assembled NASA's heat-shield engineers, the chair of the independent review team and senior human spaceflight officials to meet with outside experts — a meeting that also included two members of the press, Ars Technica reported.

This meeting included an analysis of what would happen if large sections of the heat shield were to fail completely. The engineers concluded that Orion's thick composite base, which contains a titanium framework, could keep the crew safe even if the Avcoat blocks outside it were entirely stripped away.

Danny Olivas, a former NASA astronaut and member of NASA's Advisory Council, was one of the experts who had attended the meeting and came away satisfied that NASA addressed the issue.

"NASA had a very difficult problem to solve but I'm pleased to share that team did an outstanding job of working the problem," Olivas wrote in a LinkedIn post following the meeting. "Hindsight is always 20/20 but this effort reinforced my appreciation of the commitment that NASA has to the safety and wellbeing of the crew."

However, not everyone is as confident in NASA's decision. Charles Camarda, a former NASA astronaut and heat-shield research engineer who has been publicly critical of the space agency, also attended the meeting and continued to speak out against the mission. In a response on LinkedIn, Camarda said NASA did not do its due diligence in defining and correcting the problem.

Camarda told CNN earlier this year that he had tried for months to get NASA leadership to heed his warnings. He is among a group of former NASA employees who don't believe the crew should have flown on Artemis II.

"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," Dan Rasky, an advanced entry systems and thermal protection materials expert who worked at NASA for more than 30 years, told CNN. "It's like you're at the edge of the cliff on a foggy day."

Four astronauts are flying on Artemis II: Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen. Although some experts are concerned about the astronauts, the crew has expressed confidence in the heat shield, Aerospace America reported in July 2025.

"If we stick to the new reentry path that NASA has planned, then this heat shield will be safe to fly," Wiseman said.

Macaulay, who identifies as a "nervous flyer," wouldn't bet his own life on the Artemis II heat shield. However, he noted that there were plenty of reasons to be confident ahead of Friday's reentry, including that humans would have been safe aboard Artemis I and that the Artemis II mission has been successful thus far.

"It has been an extraordinary success from a technical point of view," Macaulay said. "I think that does give reasons to be confident about the reentry because it looks like there's every reason to expect that the trajectory is going to be absolutely nominal, absolutely what it is designed for. And hopefully, that's going to give them the best possible ride through reentry. I think there really are good reasons to be confident about this."