A chemical reaction between two or more substances that releases heat, light, and gases. To launch a rocket or to move a rocket through space, we must use a propulsion system to generate thrust. Thrust is generated through an application of Newton’s third law of motion; a working gas is accelerated to the rear of the rocket engine, and the re-action is a thrust force applied to the engine in the forward direction.

In solid and liquid fuelled rocket engines, the working gas is produced through the burning of a fuel to produce power. Burning a fuel is called combustion, a chemical process that we study in middle or high school.

Because combustion is so important for rocket propulsion, we will review the fundamentals. Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat. The original substance is called the fuel, and the source of oxygen is called the oxidizer. The fuel and oxidizer can be a solid, liquid, or gas. For rocket propulsion the fuel and oxidizer are usually stored as either a liquid or a solid.

Watch this video.  What is combustion?