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: Heat shields are one of the most important parts of any spacecraft that intends to enter an atmosphere. And the material they are made of is critical.
Improving them has been a challenge, though, as researchers typically only get "before" and "after" pictures of a heat shield's job of helping a spacecraft land safely back on Earth. That changed recently with a collaboration between NASA and the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory, which allowed researchers to watch a heat shield fall apart in real time. Falling apart is also a major part of what a heat shield does.
That process, technically known as "ablation," allows the thermal energy of reentry to transfer into pieces of the material, which then fall away from the spacecraft, taking that thermal energy with them. This has long been the standard for heat shields on everything from the Mercury capsules to the Orion ones used on Artemis. There are some obvious disadvantages to the system, though.
Ablation is irreversible, and material must typically be replaced after every use. It's also exceptionally hard to simulate—for example, the recent Artemis I uncrewed test flight exhibited unexpected charring and uneven loss of ablative material that wasn't expected based on the multitude of simulations run before the mission. It's exactly that kind of unexpected, uneven physics that could result in a loss of equipment, though luckily Artemis I did successfully splash down in the Pacific Ocean.
To fix that simulation gap, scientists need to understand what is happening during the 1650℃ (3002°F) heating the materials experience during reentry, rather than simply look at the aftermath. That is where the ALS comes in. Researchers at LBNL designed a specialized chamber that exposes material to temperatures up to 900℃ (1652°F), the temperature at which heat shield material begins to break down.
It also allowed them to change the pressure and atmospheric gas composition to mimic some features of the reentry process, though a major one—air velocity—appeared to be missing from the chamber's capabilities. The big feature of ALS, though, isn't the specialized testing chamber—it's the imaging system. While the heat shield material samples were inside the chamber, they were subjected to X-ray micro-computed tomography (micro-CT).
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