Rocket engine
Solid fuel rocket motors have the fuel (called propellant) as a solid mixture of an oxidizer and fuel. An oxidizer supports the burning of fuel much like oxygen supports burning. The common oxidizer is powdered Ammonium Perchlorate, while the common fuel is powdered aluminum metal. The two powders are stuck together with a third component known as the binder. The binder is a rubbery solid that also burns as a fuel. Since their design is so simple, solid rocket engines are usually much cheaper than other rocket engines, but their main disadvantage is that they cannot be turned off, their control is very limited, and they are more likely to explode than liquid rocket engines. Solid rockets also provide a smaller specific impulse (a measure of efficiency for rocket engines), hence must be heavier to launch the same payload.