Solid rocket fuel is a solid substance (mixture of substances) that can burn without air and at the same time emit a lot of gaseous compounds heated to high temperature. Such compositions are used to create jet propulsion in rocket engines.
Rocket fuel is used as a source of energy for
rocket engines. In addition to solid fuel, there are also gel-like, liquid and hybrid analogues. Each type of fuel has its advantages and disadvantages. Liquid fuels are single-component and two-component (fuel + oxidizer). Gel-like fuels are formulations that are gelled to a gel with
organic acids. Hybrid fuels are systems that include solid fuels and liquid oxidizing agents.
The first varieties of rocket fuel were just solid. As a working substance, gunpowder and its analogues were used, which were used in military affairs and to create fireworks. Now these compounds are used only for the manufacture of small model missiles, like rocket fuel. The composition allows you to launch small (up to 0.5 m) rockets several hundred meters in height. The engine in them is a small cylinder. It is filled with a solid combustible mixture, which is ignited by a red-hot wire and burns for only a few seconds.
The solid rocket fuel most often consists of an oxidizing agent, fuel and a catalyst, which allows maintaining stable combustion after ignition of the composition. In the initial state, these materials are powdery. To make rocket fuel from them, it is necessary to create a dense and
uniform mixture that will burn for a long time, evenly and continuously. Solid propellant rocket engines use:
potassium nitrate as an oxidizing agent,
charcoal (carbon) as fuel, and sulfur as a catalyst. This is the composition of black powder. The second combination of materials that are used as rocket fuel are: Bertoletova salt, aluminum or magnesium powder and sodium chlorate. This composition is also called white powder. Solid combustible fillers for military missiles are divided into ballistic (nitroglycerin compressed gunpowder) and mixed, which are used in the form of channel blocks.
Solid propellant rocket engine operates as follows. After ignition, the fuel begins to burn at a given speed, ejecting hot gaseous matter through the nozzle, which provides traction. The fuel in the engine burns until it runs out. Therefore, it is impossible to stop the process and turn off the engine until the filler burns to the end. This is one of the serious drawbacks of solid fuel engines, compared to other analogues. However, in real space ballistic carriers, solid propellant materials are used only at the initial stage of flight. At the next stages, other types of rocket fuel are used, therefore, the disadvantages of solid fuel compositions do not pose a significant problem.