It is unclear who first invented the rocket. It is believed that, as a people, the Chinese were probably the first, as they had been using gunpowder for over 1,800 years before other countries developed its use. The Chinese were using rockets in warfare at least by the time of Genghis Khan (ca. 1155-1227).
Not long thereafter, the use of rockets spread to the west. A German named Konrad Kyster von Eichstadt, author of Bellifortis (1405) described the use of war rockets in his day.
During these decades rocketry was only used for the purpose of weapons. Sir William Congreve (1772-1828) developed incendiary barrage missiles for the British military that could be fired from either land or sea. These were used with effect against the United States in the War of 1812; it was probably Congreve’s weapons that Francis Scott Key wrote about in the "Star Spangled Banner" while imprisoned on a British warship during the bombardment of Fort McHenry at Baltimore.
The military use of rockets became outmoded later on in the 19th century (late 1800s) because of improvements in artillery which made it more accurate and destructive than rockets.
New uses for rockets were found in other industries such as whaling and for sea-going shipping where rocket-powered harpoons and rescue lines began to be employed.
How do rockets work?
From Wikipedia:
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction. Rocket engines push rockets forwards simply by throwing their exhaust backwards extremely fast.
While comparatively inefficient for low speed use, they are very lightweight and powerful, capable of generating large accelerations and of attaining extremely high speeds with reasonable efficiency, and are not reliant on the atmosphere, and so work very well in space.
Rockets for military and recreational uses were invented by the Han Chinese prior to the 13th century China. Significant scientific, interplanetary and industrial use did not occur until the 20th century, when rocketry was the enabling technology of the Space Age, including setting foot on the moon. Rockets are now used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight and space exploration.
Chemical rockets are the most common type of rocket and they typically create their exhaust by the combustion of rocket propellant. Chemical rockets store a large amount of energy in an easily released form, and can be very dangerous. However, careful design, testing, construction and use minimizes risks.
Rocket Engines
A rocket engine, or simply "rocket", is a jet engine that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law. Since they need no external material to form their jet, rocket engines can be used for spacecraft propulsion as well as terrestrial uses, such as missiles. Most rocket engines are internal combustion engines, although non-combusting forms also exist.
Rocket engines as a group have the highest exhaust velocities, are by far the lightest, but are the least propellant efficient of all types of jet engines.
Terminology
Chemical rockets are rockets powered by exothermic chemical reactions of the propellant.
Rocket motor (or solid-propellant rocket motor) is a synonymous term with rocket engine that usually refers to solid rocket engines.
Liquid rockets (or liquid-propellant rocket engine) use one or more liquid propellants that are held in tanks prior to burning.
Hybrid rockets have a solid propellant in the combustion chamber and a second liquid or gas propellant is added to permit it to burn.
Thermal rockets are rockets where the propellant is inert, but is heated by a power source such as solar or nuclear power or beamed energy.
Monopropellant rockets are rockets that use only one propellant, decomposed by a catalyst. The most common monopropellants are hydrazine and hydrogen peroxide.
Principle of operation
How rocket engines work
Rocket engines give part of their thrust due to unopposed pressure on the combustion chamber.
Rocket engines produce thrust by the expulsion of a high-speed fluid exhaust. This fluid is nearly always a gas which is created by high pressure (10-200 bar) combustion of solid or liquid propellants, consisting of fuel and oxidiser components, within a combustion chamber.
The fluid exhaust is then passed through a supersonic propelling nozzle which uses heat energy of the gas to accelerate the exhaust to very high speed, and the reaction to this pushes the engine in the opposite direction.
In rocket engines, high temperatures and pressures are highly desirable for good performance as this permits a longer nozzle to be fitted to the engine, which gives higher exhaust speeds, as well as giving better thermodynamic efficiency.
Introducing propellant into a combustion chamber Rocket propellant is mass that is stored, usually in some form of propellant tank, prior to being ejected from a rocket engine in the form of a fluid jet to produce thrust.
Chemical rocket propellants are most commonly used, which undergo exothermic chemical reactions which produce hot gas which is used by a rocket for propulsive purposes. Alternatively, a chemically inert reaction mass can be heated using a high-energy power source via a heat exchanger, and then no combustion chamber is used.
Solid rocket propellants are prepared as a mixture of fuel and oxidizing components called 'grain' and the propellant storage casing effectively becomes the combustion chamber. Liquid-fueled rockets typically pump separate fuel and oxidiser components into the combustion chamber, where they mix and burn. Hybrid rocket engines use a combination of solid and liquid or gaseous propellants. Both liquid and hybrid rockets use injectors to introduce the propellant into the chamber. These are often an array of simple jets- holes through which the propellant escapes under pressure; but sometimes may be more complex spray nozzles. When two or more propellants are injected the jets usually deliberately collide the propellants as this breaks up the flow into smaller droplets that burn more easily.
Rocket nozzles
The large bell or cone shaped expansion nozzle gives a rocket engine its characteristic shape.
In rockets the hot gas produced in the combustion chamber is permitted to escape from the combustion chamber through an opening (the "throat"), within a high expansion-ratio 'de Laval' nozzle.
Provided sufficient pressure is provided to the nozzle (about 2.5-3x above ambient pressure) the nozzle chokes and a supersonic jet is formed, dramatically accelerating the gas, converting most of the thermal energy into kinetic energy.
The exhaust speeds vary, depending on the expansion ratio the nozzle is designed to give, but exhaust speeds as high as ten times the speed of sound of sea level air are not uncommon.
Rocket thrust is caused by pressures acting in the combustion chamber and nozzle. From Newton's third law, equal and opposite pressures act on the exhaust, and this accelerates it to high speeds.
About half of the rocket engine's thrust comes from the unbalanced pressures inside the combustion chamber and the rest comes from the pressures acting against the inside of the nozzle. As the gas expands (adiabatically) the pressure against the nozzle's walls forces the rocket engine in one direction while accelerating the gas in the other.
Bibliography
Atlas of Space Exploration, Roger Launius and Andrew Johnston, Bunker Hill 2009 (Check out our local Barnes & Noble for a $9.99 copy)
No comments:
Post a Comment