“All of our conclusions, all of our recommendations were unanimously approved by our team,” Hill said. “We went to a lot of trouble, arguing sentence by sentence, to make sure the whole team agreed. To get there we certainly had some tough and energetic discussions.”
Hill did acknowledge that early in the review team's discussions, two people opposed NASA's plan to fly the heat shield unchanged. “There was clearly a disagreement early on with a few people who felt strongly that Orion's heat shield was not good enough to fly as built,” he said.
However, Hill said the IRT was convinced by NASA's thorough testing and the openness of the agencies' engineers working with them. He mentioned Luis Saucedo, a NASA engineer at NASA's Johnson Space Center, who led the agency's internal investigation into char losses.
“The work that was done by NASA was nothing short of eye-popping, it was incredible,” Hill said.
At Orion's base, which has a titanium shell, 186 blocks of a material called Avcoat are individually attached to provide a protective layer that allows the spacecraft to survive the heating of atmospheric reentry. Returning from the moon, Orion faces temperatures of up to 5,000° Fahrenheit (2,760° Celsius). A char layer that accumulates on the outer skin of the Avcoat material is expected to ablate or erode in a predictable manner during re-entry. Instead, during Artemis I, fragments fell from the heat shield, leaving voids in the Avcoat material.
Thanks to the work of Saucedo and others, including substantial testing in ground facilities, wind tunnels, and high-temperature arc blast chambers, engineers were able to determine the cause of gases becoming trapped in the heat shield and leading to cracks. Hill said his team was confident that NASA had successfully recreated the conditions observed during the reentry and, during testing, could replicate the Avcoat rupture that occurred during Artemis I.
