User:Dwindrim~enwiki/Rocket fuel

Rocket fuel is the propellant which is burned to produce thrust in rockets.

The earliest rockets were created hundreds of years ago by the Chinese. Used primarily for fireworks displays and or as armaments, they were relatively simple and were fueled by black powder. Black powder, a mixture of potassium nitrate, sulfur, and charcoal, was the only fuel for centuries, so rockets did not undergo significant design or performance capabilities during that time. In the modern era, (since the 1920s), however, rockets underwent an enormous modernization. New fuels were required to achieve the goals of scientists, through World War II and the space age.

The purpose of any basic rocket propellant is to create thrust by expelling mass backward, creating forward motion in compliance with Newton's third law of motion (for any action there is an equal and opposite reaction). Propellants burn rapidly to create hot gas, which is ejected backward at extremely high speed to achieve forward motion. It is the "equal and opposite reaction" that moves the rocket, not pushing against air. Rockets actually move faster in space, given that they do not need to overcome air resistance.

The power a propellant provides is known as specific impulse, and is a direct relationship between the weight of the fuel burned and the thrust achieved. Technological development has led to many different fuels being created for different uses in rockets. They can all be classified according to two main types, however.

Solid fuels
Solid fuels were the first type of propellant to be used in rockets. Gunpowder, obviously, was the original propellant to be used in rocketry, consisting of a mixture of charcoal, sulfur and saltpeter. Solid fuels (and really, all rocket fuels) consist of an oxidizer (substance providing oxygen) and a fuel. In the case of gunpowder, the fuel is charcoal and sulfur and the oxidizer is the saltpeter. More contemporary recipies employ such compounds as sodium or potassium chlorate and powdered aluminum. (This admixture is sometimes known as "white powder"; not only is it different in appearance for black powder, it has a considerably higher energy density.

However, even white powder, despite its improved energy per init mass, was not adequate to produce the sort of thrusts required by such devices as solid-fuel rockets and solid-fuel boosters. Thiokol Propulsion produces the standard solid-rocket fuel today, a highly-inflammabke mixture of aluminum and ammonium perchlorate which has the consistency of a pencil eraser.

The advantage of solid fuel is that, once packed in a casing, it is movement-free. Solid fuel does not leak. However, once it is ignited, there is no turning it off. (However, current research is looking at techniques for throttling solid-fuel rockets, though techniques remain in the experimental stage as of 2004.)

Liquid fuels
Liquid-fuelled engines remain the primary driving engines for contemporary spacecraft. The primary reason is that, unlike with solid rockets, liquid-fuelled engines can be started, stopped, and throttled on command, but while they have greater energy output per unit mass of fuel, they require substantially more sophisticated pumping, valving, and cooling systems.

The earliest liquid-fuel rockets, as envisioned and tested by such pioneers as Robert Goddard, employed liquid hydrogen and liquid oxygen as propellants. As fuels, these substances were highly reactive, and provided a very effective ratio between the mass of the components and the velocity of the exhaust gas. Because of this effective ratio, liquid hydrogen/liquid oxygen engines have been continued to be employed up to the present time. The primary disadvantage to this fuel combination is the difficulty in maintaining temperatures low enough to ensure that both components remain liquid.

Hydrazine is another common propellant. Unlike liquid hydrogen, it needs so oxidizer, containing it within iteslf. It is thus known as a monopropellant.

A large number of liquid propellant - oxidizer compounds are in use today; see The Planetary Society - Liquid Fuel Rockets for a comprehensive list.