Solid rocket engines are propulsion systems that use solid propellant to produce thrust. Unlike liquid rocket engines, which rely on fuel and oxidizer stored separately, solid rockets contain a mixture of fuel and oxidizer in a solid form. When ignited, the propellant burns from the inside out, generating hot gases that are expelled through a nozzle, propelling the rocket forward. These engines are commonly used in various applications, including space launch vehicles like the Space Shuttle and military missiles. Solid rocket engines are known for their simplicity, reliability, and ability to provide high thrust, making them suitable for many aerospace missions.