solidpropellant

Solid propellant, or solid rocket propellant, is a propellant in which fuel and oxidizer are chemically bound into a single solid matrix. A rocket motor filled with such a propellant burns from a surface, producing high-temperature gas that is expelled through a nozzle to generate thrust. Solid propellants are widely used in missiles, space launch boosters, and various pyrotechnic applications because they offer simple storage, long shelf life, robustness, and high density.

Propellants fall mainly into two families. Double-base propellants consist of nitrocellulose and nitroglycerin and burn as a homogeneous solid. Composite propellants combine a solid oxidizer (commonly ammonium perchlorate) with a polymer binder (such as hydroxyl-terminated polybutadiene) and a metallic fuel (typically aluminum). The propellant is cast or molded into a grain with a chosen geometry—cylindrical, star-shaped, or segmented—to control burn rate and thrust duration. Additives, stabilizers, and curing processes influence performance and aging characteristics.

In operation, ignition initiates a burning surface on the grain; the reaction generates gases that drive thrust through the nozzle. The thrust profile depends on grain geometry and burn rate, which are pressure-dependent. Solid propellants are inherently non-throttling and cannot be shut off easily once ignited, though advances in grain design and ignition can shape early thrust. They generally offer high thrust at ignition and high density but typically have lower specific impulse than cryogenic liquid propellants and are sensitive to temperature and aging.

Safety, storage, and regulatory controls apply due to the energetic nature of these materials. Solid propellants remain a foundational technology in aerospace and defense, balancing simplicity and performance with deliberate handling requirements.