Scientists Get Real-Time Look Inside Spacecraft Heat Shields During Extreme Heat Conditions

"We can perform 3D imaging of samples under different extreme conditions such as heat, cold, pressure, and tension, and we can watch the internal structure of materials evolve and give a deep look into internal structure in high detail as their properties change under these conditions," said Liz Clark, ALS scientist. "This collaboration has been a perfect application of this technique. After the first Artemis mission, where heat shields didn't perform as NASA expected from computational methods, they used the ALS to examine materials from these shields to better understand how the internal structure evolves over time."

To observe the ablators evolving, the scientists had to balance an experimental trade-off between rapidly collecting images of large, representative areas at lower resolution and capturing structural details at high resolution. To capture large sample areas quickly while preserving fine microscopic details, the researchers deployed an AI-based super-resolution method driven by generative adversarial networks.

The high-intensity broad spectrum flux from the light source allowed the team to quickly snap large-volume, lower-resolution scans at short intervals to track fast-moving structural changes. Meanwhile, switching to a single-wavelength beam enabled them to capture crisp, high-resolution snapshots of the static samples before and after the heating process.

By training the AI on these before-and-after images, they were able to enhance the entire sequence of real-time images collected during the experiment, producing a complete high-resolution record of how each material changed throughout the heating process.

The AI-enhanced imaging revealed a striking difference between the two heat shield materials. SLA-561V contains cork - the same natural material used in wine bottle stoppers - as a structural filler. When heated, the cork chemically breaks down and disappears, leaving behind open, empty pockets distributed throughout the material. SLA-220 contains no such organic filler; instead, its rubber-like silicone matrix responds to heat by forming a dense, branching network of interconnected channels.

"This is a great example of how years of working together to customize the imaging technique, and integrating AI is helping us generate high-quality data and facilitate analysis, leading to more detailed scientific insights in a fraction of the time." - Liz Clark

These are not just visual differences. Open, isolated pockets behave differently from an interconnected channel network when heat and gas move through a material at reentry conditions, and those differences affect how each material performs as a heat shield.

"This is a great example of how years of working together to customize the imaging technique, and integrating AI is helping us generate high-quality data and facilitate analysis, leading to more detailed scientific insights in a fraction of the time," said Clark.

The findings give engineers something they have not had before: direct measurements of how heat shield materials change at a microscopic level during the thermal conditions of atmospheric reentry that bolster past observational studies, improving model development and allow missions to return safely home.

The research was supported by the NASA Space Technology Research Institute and NASA Space Technology Graduate Research Opportunities program. The Advanced Light Source is a DOE Office of Science user facility at Berkeley Lab.

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