The high-speed, safe return to Earth of the Artemis 2 moon crew depends on the thermal protection system of the mission’s Orion’s crew module. It must endure blistering temperatures to keep crew members safe.
However, following the uncrewed Artemis 1 lunar flight test in late 2022, it was found that ablative thermal protective material had unexpectedly chipped away from Orion’s heat shield during its plunge through Earth’s atmosphere.
Cause of the issue
In a post-flight analysis of the Artemis 1 heat shield, NASA identified more than 100 locations where ablative thermal protective material was liberated during Orion’s speedy reentry.
NASA, along with contractors and an independent review team, launched an investigation to establish the technical cause of the issue. An analysis was done, including over 100 tests at unique facilities across the country.
The finding: Orion’s heat shield did not allow for enough of the gases generated inside a material called Avcoat to escape. This permitted pressure to build up and cracking to occur, causing some charred material to break off in several locations, NASA reported.
Beat the heat
Engineers at Lockheed Martin — the main contractor for Orion — built Orion’s heat shield and thermal protection system. Measuring 16.5 feet (5 meters) in diameter, Orion’s beat-the-heat shield is the largest of its kind developed for missions carrying astronauts.
Orion’s ablative material, Avcoat, was also used on NASA’s Apollo moon missions. However, the building process has changed since then, according to Lockheed Martin.
“Instead of having workers fill 300,000 honeycomb cells one by one with ablative material, then heat-cure the material and machine it to the proper shape, the team now manufactures Avcoat blocks — just fewer than 200 — that are pre-machined to fit into their positions and bonded in place on the heat shield’s carbon fiber skin,” the aerospace firm’s website explains. This process is a timesaver, the company has said.
A key factor
During Orion’s Artemis 1 reentry, the craft used what’s called a skip guidance entry technique.
That maneuver had Orion dipping into the upper part of Earth’s atmosphere and using atmospheric drag to reduce speed. Orion then used the aerodynamic lift of the capsule to skip back out of the atmosphere and then reenter for final descent under parachutes to splashdown.
While Artemis 1 was an uncrewed mission, NASA has said that the temperature inside Orion remained comfortable and would have been safe for astronauts, had any been aboard.
Modified trajectory
Now fast forward, quite literally, to the upcoming Artemis 2 mission, which will launch four astronauts around the moon as soon as early March.
“NASA has modified the trajectory by shortening how far Orion can fly between when it enters Earth’s atmosphere and splashes down in the Pacific Ocean,” Kenna Pell, an Orion public affairs official at NASA’s Johnson Space Center in Houston, told Space.com. “This will limit how long Orion spends in the temperature range in which the Artemis 1 heat shield phenomenon occurred.”
Similarly, Blaine Brown, Orion spacecraft mechanical systems director for Lockheed Martin, told Space.com that a tiger team — which included representatives from NASA, Lockheed Martin and an Independent Review Team — determined that a modified Artemis 2 reentry trajectory will minimize char loss and provide more than adequate margin on thermal performance.
Skip the skip
“This modified trajectory involves a slightly steeper entry profile and elimination of a skip, resulting in shorter downrange landing,” Brown said. “We performed extensive testing and analysis on the Avcoat block materials to ultimately reproduce the char liberation phenomenon seen on Artemis 1.”
Brown said that the material being used on Artemis 3 — NASA’s first human return-to-the-moon mission, targeted to launch in 2028 — is actually the same formula that was flown on Artemis 1 and that will fly on Artemis 2.
“We just slightly modified the density to allow gases in the ablative material to escape during high heating and cool down,” said Brown. “We support NASA’s decision to fly the Artemis 2 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.”
Time-sensitive challenge
All that said, a NASA Office of Inspector General (OIG) report, issued last month, focused on the return of humans to the moon.
In the NASA OIG’s 2025 Report on NASA’s Top Management and Performance Challenges, it noted that “the most time-sensitive challenge for NASA’s effort to return humans to the moon is preparing for Artemis 2.” NASA must address various challenges, the report added, to safely fly the four astronauts on the planned 10-day mission.
“While NASA considered Artemis 1 to be a near-perfect flight, it revealed technical issues that need to be addressed before Artemis 2 can launch,” the OIG report reads. “Specifically, the ablative outer material of Orion’s heat shield did not properly vent the gases normally produced during entry into Earth’s atmosphere, leading to widespread cracking and char loss.”
Root cause
Furthermore, the NASA OIG report explained that, “given NASA’s current understanding of the root cause, the Agency intends to reuse the heat shield design for Artemis 2 while flying a modified reentry trajectory that is less severe.”
While this approach is technically feasible, the report observes, “it is also complex and contingent on a successful test campaign and does not retire the heat shield risk for Artemis 3. The additional heat shield testing resulted in cascading delays to all Artemis missions starting with Artemis 2.”
During Artemis 2’s reentry, as the Orion spacecraft crew starts to feel the effects of Earth’s atmosphere for the first time since launch, superheated plasma will begin to build up around the spacecraft as the friction of the surrounding atmosphere increases.
Communications to and from the crew will be temporarily blocked by that plasma.
How the heat shield behaves this time on its modified, atmospheric deep-dive trajectory could be yet another nail-bitter.
