NASA has asked a panel of outside experts to review the agency's investigation into the unexpected loss of material from the heat shield of the Orion spacecraft on a test flight in 2022.

Chunks of charred material cracked and chipped away from Orion's heat shield during reentry at the end of the 25-day unpiloted Artemis I mission in December 2022. Engineers inspecting the capsule after the flight found more than 100 locations where the stresses of reentry stripped away pieces of the heat shield as temperatures built up to 5,000° Fahrenheit.

This was the most significant discovery on the Artemis I, an unpiloted test flight that took the Orion capsule around the Moon for the first time. The next mission in NASA's Artemis program, Artemis II, is scheduled for launch late next year on a test flight to send four astronauts around the far side of the Moon.

Another set of eyes

The heat shield, made of a material called Avcoat, is attached to the base of the Orion spacecraft in 186 blocks. Avcoat is designed to ablate, or erode, in a controlled manner during reentry. Instead, fragments fell off the heat shield that left cavities resembling potholes.

Investigators are still looking for the root cause of the heat shield problem. Since the Artemis I mission, engineers conducted sub-scale tests of the Orion heat shield in wind tunnels and high-temperature arcjet facilities. NASA has recreated the phenomenon observed on Artemis I in these ground tests, according to Rachel Kraft, an agency spokesperson.

"The team is currently synthesizing results from a variety of tests and analyses that inform the leading theory for what caused the issues," said Rachel Kraft, a NASA spokesperson.

Last week, nearly a year and a half after the Artemis I flight, the public got its first look at the condition of the Orion heat shield with post-flight photos released in a report from NASA's inspector general. Cameras aboard the Orion capsule also recorded pieces of the heat shield breaking off the spacecraft during reentry.

NASA's inspector general said the char loss issue "creates a risk that the heat shield may not sufficiently protect the capsule’s systems and crew from the extreme heat of reentry on future missions."

"Those pictures, we've seen them since they were taken, but more importantly... we saw it," said Victor Glover, pilot of the Artemis II mission, in a recent interview with Ars. "More than any picture or report, I've seen that heat shield, and that really set the bit for how interested I was in the details."