When a spacecraft reenters Earth’s atmosphere, it isn’t just “getting hot”—it’s experiencing one of the most extreme thermal environments engineered against. At speeds exceeding Mach 25, compression of air in front of the vehicle creates plasma, driving surface temperatures above 1,500°C. So how does NASA prevent catastrophic failure? The answer is thermal protection systems (TPS), specifically heat-resistant tiles like those used on the Space Shuttle. These tiles are primarily made from silica fibers—similar chemically to glass, but engineered into an ultra-low-density structure. Roughly 90% of each tile is air, which drastically reduces thermal conductivity. That means heat doesn’t travel efficiently through the material. Instead of absorbing and transferring heat inward, the tiles localize it at the surface. The outer layer can glow red-hot, while the opposite side remains cool enough to touch shortly after reentry. There are three key mechanisms at work: • Low thermal conduct...