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Inventors Early Rockets and Gunpowder - How Fireworks Work
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Fireworks displayFireworks Background: Developed in the second-century BCE, by the ancient Chinese, fireworks are the oldest form of rockets and the most simplistic model of a rocket. Originally fireworks had religious purposes in ceremonies but were later adapted for military use during the middle ages in the form of "flaming arrows." During the tenth and thirteenth centuries the Mongols and the Arabs brought the major component of these early rockets to the West: gunpowder. Although the cannon, and gun became the major developments from the eastern introduction of gunpowder, a tickling of rockets also resulted. These rockets were essentially enlarged fireworks which propelled, further than the long bow or cannon, packages of explosive gunpowder. During the late eighteenth century imperialistic wars, Colonel Congreve, developed his famed rockets, which trave range distances of four miles. The "rockets' red glare" (American Anthem) records the usage of rocket warfare, in its early form of military strategy, during the inspirational battle of Fort McHenry.

How Fireworks Function: Gunpowder, a mixture composing of: 75% Potassium Nitrate (KNO3), 15% Charcoal (Carbon), and 10% Sulfur, provides the thrust of most fireworks. This fuel is tightly packed into the casing, a thick cardboard or paper rolled up tube, forming the propellant-core of the rocket in a typical length to width or diameter ratio of 7:1.

A fuse (cotton twine coated with gunpowder) is lit by a match or by a "punk" (a wooden stick with a coal-like red-glowing tip). This fuse burns rapidly into the core of the rocket where it ignites the gunpowder walls of the interior core. One might think that the fuse would burn out once inside of the core, due to the lack of surrounding air but the chemistry of gunpowder solves this point. As mentioned before one of the chemicals in gunpowder is potassium nitrate, the most important ingredient. The molecular structure of this chemical, KNO3, contains three atoms of oxygen (O3), one atom of nitrogen (N), and one atom of potassium (K). The three oxygen atoms locked into this molecule provide the "air" that the fuse and the rocket use to burn the other two ingredients, carbon and sulfur. Thus potassium nitrate oxidizes the chemical reaction by easily releasing it oxygen. This reaction is not spontaneous though, and must be initiated by heat such as the match or "punk."

Thrust is produced once the burning fuse enters the core. The core is quickly filled with flames and thus, the necessary heat to ignite, continue, and spread the reaction. After the initial surface of the core has been exhausted a layer of gunpowder is exposed continuing, for the few seconds the rocket will burn, to produce thrust. The action reaction (propulsion ) effect explains the thrust as produced when the hot expanding gases (produced in the reaction burning of gunpowder) escape the rocket via the nozzle. Constructed of clay, the nozzle can withstand the intense heat of the flames that pass through.

The original sky rocket used a long wooden or bamboo stick to provide a low center of balance (by distributing the mass over a greater linear distance) and thus stability to the rocket through its flight. Fins usually three set at 120 degree angles of one another or four set at 90 degree angles of one another, had their developmental roots in arrow feather guides. The principles that governed the flight of an arrow were the same for early fireworks. But fins could be omitted altogether since a simple stick seemed to grant sufficient stability.  Only when firework-type rockets became more developed did the fin rocket gain popularity.  With fins properly set (in creating a suitable center of balance) the extra mass of the drag (air resistance) creating guide-stick could be removed, increasing rocket performance. Also, as rockets become larger and more powerful the exhaust from the engine would consume the guide-stick, destroying the rockets mode of guidance.

Fireworks have remained popular in today's age due to the spectacle of colors and sounds they are so renown for. The component of a rocket that produces these stars, reports ("bangs"), and colors is typically located just below the nosecone section of a rocket. After the rocket engine has consumed all of its fuel an internal fuse is lit that delays the release of the stars, or other effect. This delay allows for coasting time where the rocket continues its ascent. As gravity will eventually pull the firework back to earth, it slows and eventually reaches an apex (highest point: where velocity of the rocket is zero) and begins its descent. The delay usually lasts just before this apex, at an optimum velocity, where a small explosion shoots the firework's stars in desired directions and thus producing a brilliant effect. The colors, reports, flashes, and, stars are analogous to flavor one adds with spices (chemicals with special pyrotechnic properties) to a soup of otherwise bland gunpowder.

Advantages/Disadvantages: Gunpowder's relatively low specific impulse (amount of thrust per unit propellant) limits its capacity of thrust production on larger scales. Fireworks are the simplest of solid rockets and the weakest. Evolution from fireworks brought about more complex solid fueled rockets, which use more exotic and powerful fuels. The low-explosive properties of gunpowder, relative to the high-explosive properties of more advanced solid fuels testify to the "survival of the fittest," as the use of firework-type engines (for purposes other than entertainment or education) has virtually ceased since the late ninteenth century. Yet with all these drawbacks fireworks will continue to maintain their use as a traditional pastime with an on-going history of nearly 5,000 years.

Gunpowder History
Taoist alchemists were major force behind the early invention of gunpowder. Emperor Wu Di (156-87 B.C.) of the Han dynasty financed research done by the alchemists on the secrets of eternal life. The alchemists experimented with the sulphur and saltpeter heating the substances in order to transform them. The alchemist Wei Boyang wrote the "Book of the Kinship of the Three" detailing the experiments. During the 8th century Tang dynasty, sulphur and saltpeter were first combined with charcoal to create an explosive called huoyao or gunpowder. A substance that did not encourage eternal life, however, gunpowder was used to treat skin diseases and as a fumigant to kill insects before its advantage as a weapon was made clear.

From Other Guides:
Chemistry of Firework Colors

Partial information provided by NASA/Writer Robert Lobbia
This research has made use of the Astronomical Data Center (ADC) at NASA Goddard Space Flight Center.
Photo Mary Bellis
 

From Mary Bellis,
Your Guide to Inventors.
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