Heat Shields & TPS

Explore ablative shields like PICA-X and AVCOAT, ceramic tiles from the Space Shuttle, and Starship’s next-generation hex tiles. Understand the physics of re-entry heating and how each material protects the spacecraft behind it.

A capsule returning from low Earth orbit hits the atmosphere at roughly 7.8 km/s — about 28,000 km/h. Almost all of the heat comes from shock-compressing the air ahead of the vehicle, not friction: the gas in that shock layer can exceed 1,650 °C (3,000 °F). Spacecraft coming back from the Moon arrive even faster — Apollo and Orion re-enter near 11 km/s, and NASA’s Stardust sample capsule set the human-made record at 12.9 km/s in 2006.

Thermal protection comes in two families. Ablative shields char and slowly erode, carrying heat away as the surface burns off: NASA’s PICA (Phenolic Impregnated Carbon Ablator) flew on Stardust, SpaceX’s denser PICA-X variant protects Crew Dragon, and AVCOAT lined the Apollo command module and now coats Orion. Reusable systems instead re-radiate heat — the Space Shuttle carried roughly 24,000 individually-shaped silica tiles plus reinforced carbon-carbon on its nose cap and wing leading edges, while SpaceX’s Starship uses around 18,000 hexagonal ceramic tiles engineered for rapid reflight without refurbishment.