A CM (Command Module) heat shield refers to the protective covering on the re-entry module of a spacecraft, specifically the Apollo Command Module used in NASA's Apollo program. The purpose of the CM heat shield is to protect the astronauts and the spacecraft itself during re-entry into the Earth's atmosphere.
During the Apollo missions, the Command Module orbited the Moon and then returned to Earth. When re-entering the Earth's atmosphere, the CM experienced extremely high temperatures caused by the intense friction between the spacecraft and the air molecules. The heat shield played a critical role in managing this heat by effectively dissipating it and preventing the CM from overheating or burning up.
The CM heat shield was made of a material called ablator, specifically a type known as "Avcoat." Ablators are designed to absorb and dissipate heat by undergoing a controlled process of ablation. As the spacecraft re-entered the atmosphere, the heat shield's outer surface would gradually erode or ablate, carrying away the heat and preventing it from penetrating deeper into the CM.
The CM heat shield was a vital component of the re-entry system, ensuring the survival of the astronauts and the integrity of the spacecraft during the fiery re-entry phase. Its design and materials were carefully engineered to withstand the extreme heat and protect the occupants and critical systems inside the Command Module.