rocket (redirected from Rocket (aeronautics))

rocket, in botany

rocket, in botany, popular name for several plants of the family Cruciferae (mustard family). The dame's, or damask, violet, damewort, or sweet rocket is Hesperis matronalis, a hardy, herbaceous Old World perennial with four-petaled flowers, ranging from white to purple, that are especially fragrant in the evening. It grows wild in many parts of North America, where it has escaped from gardens. Rocket salad (Eruca sativa) is the roquette of France and Italy and is a coarse, weedy plant with whitish or creamy-yellow flowers that have an orange-blossom odor. Also known as tira and garden rocket, it is cultivated for salads. Yellow rocket (Barbarea vulgaris) is the name for a variety of winter cress or upland cress, a weedy plant sometimes cultivated for salads. Among the North American wildflowers called rocket are the prairie-rocket (Erysimum asperum), the purple rocket (Iodanthus pinnatifidus), and the sea rocket (Cakile edulenta). The latter, like related European species, grows along seacoasts. The unrelated dyer's rocket, or dyer's-weed, is Reseda luteola, a species of mignonette. Rockets are classified in the division Magnoliophyta, class Magnoliopsida, order Capparales, family Cruciferae.

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rocket, in aeronautics

rocket, any vehicle propelled by ejection of the gases produced by combustion of self-contained propellants. Rockets are used in fireworks, as military weapons, and in scientific applications such as space exploration.

Rocket Propulsion

The force acting on a rocket, called its thrust, is equal to the mass ejected per second times the velocity of the expelled gases. This force can be understood in terms of Newton's third law of motion, which states that for every action there is an equal and opposite reaction. In the case of a rocket, the action is the backward-streaming flow of gas and the reaction is the forward motion of the rocket. Another way of understanding rocket propulsion is to realize that tremendous pressure is exerted on the walls of the combustion chamber except where the gas exits at the rear; the resulting unbalanced force on the front interior wall of the chamber pushes the rocket forward. A common misconception, before space exploration pointed up its obvious fallacy, holds that a rocket accelerates by pushing on the atmosphere behind it. Actually, a rocket operates more efficiently in outer space, since there is no atmospheric friction to impede its motion.

Rocket Design

The key elements in designing a rocket are the propulsion system, which includes the propellant and the exit nozzle, and determining the number of stages required to lift the intended payload. Rocket navigation is usually based on inertial guidance; internal gyroscopes are used to detect changes in the position and direction of the rocket.

Rocket Propellants

The most vital component of any rocket is the propellant, which accounts for 90% to 95% of the rocket's total weight. A propellant consists of two elements, a fuel and an oxidant; engines that are based on the action-reaction principle and that use air instead of carrying their own oxidant are properly called jets. Propellants in use today include both liquefied gases, which are more powerful, and solid explosives, which are more reliable; the space shuttle's main engines use liquid propellant, while its boosters are solid-fuel rockets. The chemical energy of the propellants is released in the form of heat in the combustion chamber.

A typical liquid engine uses hydrogen as fuel and oxygen as oxidant; a typical solid propellant is nitroglycerine. In the liquid engine, the fuel and oxidant are stored separately at extremely low temperatures; in the solid engine, the fuel and oxidant are intimately mixed and loaded directly into the combustion chamber. A solid engine requires an ignition system, as does a liquid engine if the propellants do not ignite spontaneously on contact.

The efficiency of a rocket engine is defined as the percentage of the propellant's chemical energy that is converted into kinetic energy of the vehicle. During the first few seconds after liftoff, a rocket is extremely inefficient, for at least two unavoidable reasons: High power consumption is required to overcome the inertia of the nearly motionless mass of the fully fueled rocket; and in the lower atmosphere, power is wasted overcoming air resistance. Once the rocket gains altitude, however, it becomes more efficient. as the trajectory, at first vertical, curves into a suborbital arc or into the desired orbit.

Although all known rockets currently in use derive their energy from chemical reactions, more exotic propulsion systems are being considered. In ion propulsion, a plasma (ionized gas consisting of a mixture of positively charged atoms and negatively charged electrons) would be created by an electric discharge and then expelled by an electric field. The engine could provide a low thrust efficiently for long periods; on a lengthy flight this would produce very high velocities, so that if there is ever a trip to the outer planets an ion drive might be used. Deep Space 1, a space probe launched in 1998 to test new technologies, was propelled intermittently by an ion engine. Even nuclear power has been considered for propulsion; in fact, a nuclear ramjet was developed in the early 1960s before it was realized that because the exhaust gases would be highly radioactive such a drive could never be used in earth's atmosphere.

Design of the Exit Nozzle

A critical element in all rockets is the design of the exit nozzle, which must be shaped to obtain maximum energy from the exhaust gases moving through it. The nozzle usually converges to a narrow throat, then diverges to create a form which shapes the hypersonic flow of exhaust gas most efficiently. The walls of the combustion chamber and nozzle must be cooled to protect them against the heat of the escaping gases, whose temperature may be as high as 3,000°C;—above the melting point of any metal or alloy.

Staging of Rockets

Although early rockets had only one stage, it was early recognized that no single-stage rocket can reach orbital velocity (5 mi/8 km per sec) or the earth's escape velocity (7 mi/11 km per sec). Hence multistage rockets, such as the two-stage Atlas-Centaur or the three-stage Saturn V, became necessary for space exploration. In these systems, two or more rockets are assembled in tandem and ignited in turn; once the lower stage's fuel is exhausted, it detaches and falls back to earth. Soviet systems clustered several rockets together, operated simultaneously, to obtain a large initial thrust.

Development of Rockets

The invention of the rocket is generally ascribed to the Chinese, who as early as A.D. 1000 stuffed gunpowder into sections of bamboo tubing to make military weapons of considerable effectiveness. The 13th-century English monk Roger Bacon introduced to Europe an improved form of gunpowder, which enabled rockets to become incendiary projectiles with a relatively long range. Rockets subsequently became a common if unreliable weapon. Major progress in design resulted from the work of William Congreve, an English artillery expert, who built a 20-lb (9-kg) rocket capable of traveling up to 2 mi (3 km). In the late 19th cent., the Austrian physicist Ernst Mach gave serious theoretical consideration to supersonic speeds and predicted the shock wave that causes sonic boom.

The astronautical use of rockets was cogently argued in the beginning of the 20th cent. by the Russian Konstantin E. Tsiolkovsky, who is sometimes called the "father of astronautics." He pointed out that a rocket can operate in a vacuum and suggested that multistage liquid-fuel rockets could escape the earth's gravitation. The greatest name in American rocketry is Robert H. Goddard, whose pamphlet A Method for Reaching Extreme Altitudes anticipated nearly all modern developments. Goddard launched the first liquid-fuel rocket in 1926 and demonstrated that rockets could be used to carry scientific apparatus into the upper atmosphere. His work found its most receptive audience in Germany. During World War II, a German team under Wernher von Braun developed the V-2 rocket, which was the first long-range guided missile. The V-2 had a range greater than 200 mi (322 km) and reached velocities of 3,500 mi (5,600 km) per hr.

After the war, rocket research in the United States and the Soviet Union intensified, leading to the development first of intercontinental ballistic missiles and then of modern spacecraft. Important U.S. rockets have included the Redstone, Jupiter, Atlas, Titan, Agena, Centaur, and Saturn carriers. Saturn V, the largest rocket ever assembled, developed 7.5 million lb (3.4 million kg) of thrust. A three-stage rocket, it stood 300 ft (91 m) high exclusive of payload and with the Apollo delivered a payload of 44 tons to the moon. Rockets presently being used to launch manned and unmanned missions into space include the U.S. Athena 1 and 2, Taurus, Titan 2 and 4B, Delta 2, 3, and 4, Atlas 2 ,3, and 5, and STS or space shuttle; the Chinese Long March 2C, 2E, and 2F; the Russian Soyuz and Proton K and M; the Japanese H-2A; the European Space Agency's Ariane 5 series; the Indian PSLV (Polar Satellite Launch Vehicle); the Israeli Shavit 2; the Brazilian VSV-30; and the multinational, private Sea Launch Zenit-3SL, which uses a converted oil platform located some 1,400 mi (2,250 km) southeast of Hawaii.

See also space science.

Bibliography

See G. P. Sutton, Rocket Propulsion Elements: An Introduction to the Engineering of Rockets (6th ed. 1992); F. H. Winter, Rockets into Space (1993); D. Baker, Spaceflight and Rocketry: A Chronology (1996); M. Stoiko, Pioneers of Rocketry (1997); R. Snedden, Rockets and Space (1998).

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rocket

Type of jet-propulsion device that uses either solid or liquid propellants to provide the fuel and oxidizer needed for combustion. The hot gases provided by combustion are ejected in a jet through a nozzle at the rear of the rocket. The term is also commonly applied to any of various vehicles, including fireworks, skyrockets, guided missiles, and launch vehicles for spacecraft, that are driven by such a propulsive device. Typically, thrust (force causing forward motion) is produced by reaction to a rearward expulsion of hot gases at extremely high speed (see Newton's laws of motion).

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rocket

1. a Mediterranean plant, Eruca sativa, having yellowish-white flowers and leaves used as a salad: family Brassicaceae (crucifers)

2. any of several plants of the related genus Sisymbrium, esp S. irio (London rocket), which grow on waste ground and have pale yellow flowers

3. yellow rocket any of several yellow-flowered plants of the related genus Barbarea, esp B. vulgaris

4. sea rocket any of several plants of the related genus Cakile, esp C. maritima, which grow along the seashores of Europe and North America and have mauve, pink, or white flowers

5. dame's rocket another name for dame's violet See also dyer's rocket wall rocket

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rocket [′räk·ət]

(aerospace engineering)

Any kind of jet propulsion capable of operating independently of the atmosphere.

A complete vehicle driven by such a propulsive system.