Rubber Based Rockets
There are two principle types of rocket engines: liquid; and solid. Nuclear rocket engines have never left the test bed and ion engines are so rare they barely warrant a mention.
Despite having a lower specific impulse, solid propellant rockets have several inherent advantages over liquid propellant rockets, i.e., simple construction and long shelf-life.
There are three principle classes of solid propellant:
Black powder was introduced by the Chinese as early as the 13th century. It was still in use by the military up to the beginning of World War II. Today, it is still in use for fireworks and model rockets. Technically, black powder is a composite propellant as it consists of a separate fuel and oxidiser which are intimately mixed.
Composite propellant was introduced in 1936. It consists of an organic fuel material mixed with an oxidiser. The first example used aspalt as a fuel/binder with potassium perchlorate as an oxidiser. Aspalt was quickly replaced by synthetic rubber. Today, a wide range of rubber binders are available. In some compositions the rubber functions as both fuel and binder. In other compositions the rubber is only a binder, with powdered aluminium acting as the fuel.
Double base propellant
Regardless of chemical composition, several options are available for the physical design of solid propellant rockets.