Solid propellants are a type of fuel used in rockets and missiles that remain in a solid state during combustion. They consist of a mixture of fuel and oxidizer, which are combined into a single solid form. When ignited, the chemical reaction produces hot gases that expand and are expelled through a nozzle, generating thrust. These propellants are popular due to their simplicity and reliability. Unlike liquid propellants, which require complex storage and handling systems, solid propellants can be stored for long periods without significant degradation. They are commonly used in military applications and space exploration, such as in NASA's Space Shuttle boosters.