Solid rocket fuels

Solid rocket fuels contain three main different components:

Fuel. The fuel can be nitrogen-based, fine magnesium powder or fine aluminum powder, or anything that burns quickly and releases a lot of energy.

Oxidiser. In order to burn, the fuel must combine with an oxidiser. In the atmosphere, ramjets and normal engines can combine with oxygen in the air, but most solid-fuel rockets include an oxidiser such as nitrocellulose or a perchlorate. Mixing the oxidiser with the fuel allows a hotter, more even burn.

Binding agent. This holds the fuel and oxidiser together in "grains" allowing it to burn more efficiently. It also makes the consistency of the fuel the same throughout. Binding agent is usually plasticene in character and turns the fuel roughly the consistency of rubber eraser.

Curing agent is also used in a very small amount. It is used to harden the fuel so that it is easier to transport and does not make as much of a mess. It also helps prevent the fuel from dripping and becoming inconsistent and layered. (source 3)

Eventually, the fuel in a solid rocket begins to collapse and become inconsistent, due to the binder breaking down and the fuel grains separating. If this happens, the rocket has a high potential of blowing up in flight. The fuel in a solid-fuel US military Minuteman ICBM will last approximately 3 years before needing to be replaced. (source 10) Many fuels take much longer or shorter to break down. This is dependent on the composition of the fuel and its consistency.

The two most common propellants are the US-developed propellant balistite (used in smaller rockets and guided missiles) and the Russian-developed propellant cordite (same purpose). They are very similar and have the following composition:

(source: 4)

These fuels are highly stable, burn very efficiently, and have a long shelf life, which is very important in military applications. The fuels must not be set off by bumping or jarring which often occurs in combat and must store for long periods of time (often in adverse conditions) before use.

At left, a German army soldier with the Milan portable antitank missile. At right, a Soviet AT-4 missile. The two are functionally identical and their key difference (besides warhead and guidance system) is their propellants- Ballistite for the Milan and Cordite for the AT-4. Source: http://www.fas.org/man/dod-101/sys/land/row/

The formuals for all rocket fuel are developed using our buddy the mole. That's right. The percentages above in Ballistite and Cordite are somewhat strange, but this is due to the differeing masses. With the data above, it might also be possible to use an empirical formual to determine the exact reaction in the formula. However, this may not be possible since the exact formula of both forms of nitrocellulose are not disclosed, and the other items included in the propellant are also not specified.

Many cheaper propellants (used in large-size model rockets and cheaper weapons such as rocket-propelled grenades) are based on aluminum or magnesium since these materials are much cheaper, even though they provide less thrust. Several common metal-based propellants are listed below:

(source: 6)

The burn rates of the two and the burn characteristics are very different. The aluminum based fuel has superior velocity and a slower burn rate(1600 meters/second velocity, 12mm/second burn rate) compared to the polyester based fuel, which has a veolcity of 1120 meters/second and a burn rate of 18mm per second. The polyester based fuel is also much cheaper, but the flame has a temperature of over 3500¼C and produces corrosive potassium chloride gas. This means that the nozzle on the rocket must be made out of graphite for a burn of over about 4 seconds. A metal nozzle will corrode and melt. Aluminum based propellants have colder flames and don't produce corrosive gasses, meaning that they can be used with a standard metal nozzle. (source: 6)

That's all for fuels... go on and check something else out.