Heat shield

The protective outer layer that lets a spacecraft survive the intense heating of re-entry into the atmosphere.

• Returning from orbit at about 7.8 km/s, the air compressed ahead of the vehicle reaches thousands of degrees; the shield keeps the structure cool.
• Ablative shields char and erode on purpose, carrying heat away as they do; they work well but are generally single-use.
• Reusable ceramic tiles, used on the Space Shuttle and Starship, insulate instead, but they are brittle and fitted with small gaps.
• A damaged wing-edge panel doomed Columbia in 2003; a shield that survives many flights with little refurbishment is key to full reuse.