Follow Up: More Detail, On The Heat Shield Issues -- On Artemis/Orion/Starliner, From NASA Materials Engineers.

This is why there will be added delays, in any "live humans, in boots, on the surface" missions, anywhere beyond Earth.

As we mentioned two days ago, it was wise to bring that last Starliner home without her crew. No one would have been in danger, but the unexpected nature of these gas bubbles causing cracks and ablation beyond specs. . . clearly means either a redesign, or added testing here on Earth, for more shallow re-entry profiles, and thus less violent temperature increases and drops, and aims for shorter durations at highest temperatures.

Here's the latest, from NASA's excellent root cause analysis teams:

. . .After extensive analysis and testing, NASA has identified the technical cause of unexpected char loss across the Artemis I Orion spacecraft’s heat shield.

Engineers determined as Orion was returning from its uncrewed mission around the Moon, gases generated inside the heat shield’s ablative outer material called Avcoat were not able to vent and dissipate as expected. This allowed pressure to build up and cracking to occur, causing some charred material to break off in several locations.

“Our early Artemis flights are a test campaign, and the Artemis I test flight gave us an opportunity to check out our systems in the deep space environment before adding crew on future missions,” said Amit Kshatriya, deputy associate administrator, Moon to Mars Program Office, NASA Headquarters in Washington. “The heat shield investigation helped ensure we fully understand the cause and nature of the issue, as well as the risk we are asking our crews to take when they venture to the Moon. . . .”

Using Avcoat material response data from Artemis I, the investigation team was able to replicate the Artemis I entry trajectory environment -- a key part of understanding the cause of the issue -- inside the arc jet facilities at NASA’s Ames Research Center in California. They observed that during the period between dips into the atmosphere, heating rates decreased, and thermal energy accumulated inside the heat shield’s Avcoat material. This led to the accumulation of gases that are part of the expected ablation process. Because the Avcoat did not have “permeability,” internal pressure built up, and led to cracking and uneven shedding of the outer layer. . . .

So -- now we wait to see what path is best, for next potential crewed mission and return. But it may entail a redesign. If so, that puts the crewed Mars mission beyond 2030, in my estimation. Now you know. Onward.

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