Whta is a heat shield?

   Heat shield is a covering on a spacecraft or a rocket nose cone. It protects astronauts and instruments from the intense heat produced during high-speed flights through the atmosphere. Such heating occurs when a spacecraft descends from an earth orbit. Atoms and molecules of air generate heat by friction against the surface of the craft. The greater the craft's velocity, the more intense the heat. Common types of heat shields are heat sinks and ablation shields. Heat sinks absorb great amounts of heat, thus preventing heat from reaching delicate parts of the spacecraft. Ablation shields use up heat by melting and vaporizing. The air stream carries the molten particles and hot gas vapor away from the craft.