Solid-fuel rocket

A solid rocket motor (also solid rocket propulsion ) is a rocket engine with a power set of solid material. Both reducing and oxidizing components are carried bound as solids. In contrast, there is a liquid-fueled rocket, should be included with both the oxidant and the reducing fuel in liquid form, mixed and burned. The combination of the two types are called hybrid rocket.

The historically oldest types of rockets are solid- based. There were long at all only built solid rocket. Although they have some disadvantages compared to more modern types of rockets, they are widely in use because of important advantages to this day.


Solid rocket come - you can see applications with swiveling nozzles from - from without any moving parts or additional devices for fuel pump or lines, which would provide a minimum level of technical mass. They also contain their fuel at all times, so that storage and refueling facilities are not required. This facilitates for example the application for meteorological or ground-based scientific purposes; for military use, they can sometimes be stored or carried in larger numbers in magazines and are operational in a short time.

The fuel itself is - eponymous for the drive - proof and therefore much easier to handle than liquid or gaseous fuels: it can not escape in this form and so may contribute to health or harmful to the environment, yet chemically react with pipe or tank walls. Instabilities due to sloshing liquid fuel ( Pogoeffekt ) fall away when the solid propellant. The shape of the propellant, the so-called burning characteristic, ie seen the development thrust over the burn time, and the firing duration itself is very easy to influence. As well as shear forces are achieved, which are larger than the liquid engines. Besides bringing the most propellant forms that the center of gravity of the rocket during the burn relatively little change, which is important for the flight stability.

These advantages to solid rocket boosters are reliable in use, powerful and inexpensive to develop, manufacture, maintain and use.


Since solid rocket containing their highly explosive fuel always comes of them permanently with an increased risk of. Also they are characterized heavier than similarly sized liquid propellant rockets, which can be transported empty and filled up only when needed.

The products of combustion of solid fuel rockets are mostly ejected at a lower speed than the products of combustion of liquid-fuel rockets. Since the thrust of the formula calculates their advantage of high shear force by a high consumption of fuel must be bought. This causes the liquid against missiles short focal length. A short-term, unplanned thrust control during the burn-off is not possible. Can only in the manufacture of the booster, for example, by the filling of different segments with different reactive fuel mixtures, or by the shape of the fuel (see below), the sliding profile can be influenced by the burning time.

The entire interior of a solid-fuel rocket is at the same time its combustion chamber. In the combustion of the fuel, very high pressures. Therefore, the walls of relatively heavy steel must be made. Since with increasing size of the rocket, the load on the combustion chamber wall increases more and more with the same internal pressure, the walls need to be getting thicker and thus heavier. Thus, the empty weight of a solid rocket rises compared to the total mass with increasing size ever, while she continues to fall in liquid-propellant rocket. Therefore, your maximum technical mass is less than that of other types of rockets.

Solid rocket boosters are often harmful to the environment than other types of buildings. In the combustion of the fuel leads according to the filling eg Chlorine gas, hydrogen chloride, sulfur compounds or other toxic substances.

Fuel geometry and thrust force curve

In the simplest case, such as in fireworks, the entire interior of the solid-fuel rocket is filled with the fuel. This burns from back to front evenly. With only a short burn time this is not a problem; at longer focal length, however, it leads to a very high thermal load of the rear, an "empty" part of the rocket, the flow through the hot combustion gases.

A further possibility is to form the fuel to a hollow tube which burns from the inside out. Here, the remaining rocket fuel acts as a heat insulator, protecting the rocket shell from overheating. With increasing extension of the cavity, however, also increases the thrust of the engine, since it is approximately proportional to the surface of the burning fuel. In contrast missile is highest usually in the start phase of the thrust requirement because the missile is here hardest and still needs to be accelerated.

However, by appropriate shaping of the cross section of the fuel tube, the thrust curve can be influenced so that it corresponds to the requirements. Thus, the cavity may be formed as a star shape. During ignition the surface of the burning fuel is at a maximum; " Pip " for the burning off of the fuel, the cross section is approximately circular and the fuel surface, and the thrust is thus low.


The earliest rockets were solid-fuel rockets. They were probably built by the Byzantines in the seventh century AD, composed of bamboo as rocket body and a mixture of nitric and sulfur as fuel.

Presumably, regardless of the Chinese in the 13th century rockets were developed which were powered by black powder. There they were used among other things for military purposes. In Europe, it later became known, their main importance they had here but at first only as a firecracker.

The British officer William Congreve developed in the early 19th century, a rocket for military use. However, by the progress of the artillery, the rocket experienced a shadowy existence. Only at the end of the 19th century was again strengthened its research and development in this area.

The first successful launch of a solid-fuel rocket in Europe missile test (1931 ) by Karl Poggensee and Reinhold Tiling is called.


Solid rocket boosters are used differently today, both for military and civilian purposes, such as aerospace. They are used because of their low price, especially to help launch rockets ( "booster" ) and planes ( JATO ) and in small high school drives. They may also be due to their high maximum acceleration as a rescue rocket use to bring manned spaceships quickly out of the danger zone of a failing launch vehicle.

As an oxidizer, for example, at APCP ammonium perchlorate ( NH4ClO4 ) used the example in the decay 4 H2O N2 2 O2 Cl2 yields ( it arises in practice, HCl). Oxygen and chlorine react with aluminum to Al2O3 and AlCl3 and a polymeric binder hydrocarbon ( plastic) to H2O and CO2, with further energy is released. The mass fraction of aluminum is up to 30 percent.

Through its simple design solid rocket boosters can be applied, for example as small rockets for fireworks, signaling or as a special missiles for the hand weapons., Even in very small size This rather simple propellant such as black powder to be used.


In the future it is planned to reduce the high curb weight of large solid rocket by the steel material is replaced by carbon-fiber- reinforced plastics. Thus, the empty mass of large solid rocket could be drastically reduced. Calculations showed that one of the full -to empty mass ratio, the payload of the Ariane 5 could with the aim Geostationary transfer orbit around 2 t increase solely by this improvement.

These lightweight materials could also allow pure solid rocket transporting large satellites economically in low earth orbits.