Reentry is the hardest part of spaceflight to survive. A spacecraft coming back from orbit hits the atmosphere at many times the speed of sound, and the air in front of it cannot get out of the way fast enough. It compresses, heats up, and wraps the vehicle in plasma hotter than molten lava. Starship's answer to that inferno is a blanket of thousands of black hexagonal heat shield tiles, and making them stay on has been one of the program's longest engineering battles.

Starship's structure is stainless steel, which handles heat better than aluminium but cannot survive reentry temperatures on its own. The hottest parts of the ship during reentry, the belly and the leading edges of its flaps, face temperatures in the range of 1,400 degrees Celsius and beyond. Without protection, the steel would weaken, warp and fail. The tiles take that punishment instead, insulating the structure beneath them.

The tiles are made of a silica-based ceramic, similar in spirit to the tiles that protected the Space Shuttle, but designed for a different job. Shuttle tiles were fragile, individually fitted, and needed enormous maintenance between flights. Starship's tiles are meant to be mass-produced, mechanically attached, and reused with minimal refurbishment, because a rapidly reusable rocket cannot spend months in a tile shop after every flight.