About Orion's Heatshield Issues

Thanks to a tip from SpaceNews.com, I learned that NASA's office of the Inspector General released a report on May 1 covering the aspects of the Artemis 1 mission that are behind the reschedule of Artemis 3 from the end of this year until NET September of '25. In particular, they cover the heat shield issues with photographs that I haven't seen yet. Seeing them shines a whole new light on the investigation. 

The report reviewed problems with the Orion spacecraft, as well as ground equipment and the Deep Space Network, from the uncrewed Artemis 1 mission launched in November 16, 2022. The entire report, 43 pages, is here at the OIG's site. It can be downloaded directly as a pdf. 

The problem that's discussed the most is the heat shield, as mentioned as recently as last Saturday. 

NASA disclosed months after the flight that more of the ablative heat shield material had been lost during reentry than expected, but added that it has not posed a safety risk to the spacecraft.
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According to the OIG report, NASA found more than 100 locations on the heat shield where material “chipped away unexpectedly” during the Artemis 1 reentry. The report included images showing pockmarked portions of the heat shield that had not previously been released by the agency.

"More than 100 locations" isn't a safety risk? They include one photograph. 

To me, that looks terrible, but I'll be the first to admit that I'm radio designer, and know next to nothing about heat shields.

The heat shield material, known as Avcoat, “wore away differently than NASA engineers predicted, cracking and breaking off the spacecraft in fragments that created a trail of debris rather than melting away as designed,” the report stated. “The unexpected behavior of the Avcoat 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.”

NASA has yet to find a root cause for the behavior of the heat shield material. In a response accompanying the report, Cathy Koerner, NASA associate administrator of exploration systems development, stated that ground testing “successfully recreated char loss” and that that the material in those tests “has the same features as observed on the Artemis I heat shield.” But the OIG report noted that while NASA was able to recreate the char loss, “they could not reproduce the exact material response or flight environment experienced during Artemis I.”

NASA has yet to identify a root cause of the behavior seen on Artemis I, and they consider that the biggest risk for the next Artemis mission. Amit Kshatriya, deputy associate administrator for the Moon to Mars Program, said their emphasis was to understand the physics going on here. 

“We’re getting close to the final answer in terms of that cause,” he said, while others analyze potential changes in the reentry trajectory to alter the heat load on the capsule.

“When we stitch it all together, we either will have flight rationale or we won’t,” he concluded. He didn’t estimate when that would be done, although NASA’s response to the OIG report offered a planned completion date of June 30. 

In addition to this big problem, there was another one in the same heat shield area. Three of four separation bolts on the base of the heat shield, used to separate the service module before reentry, experienced “unexpected melting and erosion” that post-flight analysis blamed on a “thermal model discrepancy.”

The bottom right picture looks more like corrosion on top of the molten bolt than just being melted, perhaps corrosion from being in saltwater. The answer is they'll design that area differently for use after Artemis II, but for the next mission, they've made some minor design changes to the bolt and will add some more heat resistant stuff around the bolt.