This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When a spacecraft reenters Earth's atmosphere at hypersonic velocities, its protective heat shield faces extreme conditions, including temperatures beyond 3,000 degrees Fahrenheit (1,650 degrees Celsius). To survive, the shield relies on specialized materials that absorb heat as they degrade in a controlled process called ablation, sacrificing the shield's outer layers to protect the vehicle and crew within.
Designing those materials requires understanding exactly how they degrade. But watching that process at the microscopic level in enough detail to capture the necessary information has been a challenge, forcing engineers to rely on observations made before and after testing to develop computational models. At the Advanced Light Source (ALS) at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), researchers found a way to watch ablation in real time.
They used a sample environment on an X-ray tomography instrument that independently controls temperature, pressure and gas mixture to recreate realistic, evolving reentry conditions. Findings from a recent study carried out in part at the ALS offer detailed, time-lapse 3D images of this process, improving how engineers model and design thermal protection systems for space missions, including NASA's recent Artemis missions. The research is published in the journal npj Materials Degradation.
"Directly observing how heat shield materials degrade during heating with this technique has been transformative for atmospheric entry research since it gives us unique insights and helps us visualize the internal structural changes that drive ablation as it occurs," said Vishnu Oruganti, who was a postdoctoral fellow at the University of Illinois Urbana-Champaign at the time of the study and is now a researcher at NASA's Johnson Space Center in Houston. "Nearly every major NASA ablative heat shield material has been studied with this technique at the Advanced Light Source, including those relevant to the Artemis and Mars entry missions." As part of a long-term collaboration with the ALS, a team of researchers from the University of Illinois Urbana-Champaign and NASA used in situ X-ray micro-computed tomography, known as micro-CT, to peer inside a class of heat shield materials called superlight ablators, the same kind used on the backshells of NASA spacecraft. The team pushed the technique further than ever before by heating the samples to 1,652 degrees Fahrenheit (900 degrees Celsius), the upper end of the temperature range in which the materials begin to decompose, and imaging them on the micrometer scale at multiple time points.
The researchers studied two commercial ablators, SLA-220 and SLA-561V, which are used in different parts of spacecraft backshells and have different compositions. Through micro-CT, they tracked how high-temperature heating similar to atmospheric reentry affects real-time multiphase chemical decomposition and porosity. These measurements provide data for developing and validating predictive models, reducing uncertainty in heat shield performance, improving mission planning and ultimately helping ensure the safety and reliability of future crewed exploration missions.
"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 ALS scientist Liz Clark. "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." Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly.
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