Avril Girl

Sunday, 10 July 2011

Rocket

Rocket


A Soyuz-U, at Baikonur Site 1/5
Apollo 15 launch.ogg
Launch of Apollo 15 Saturn V rocket: T - 30 s through T + 40 s
A rocket or rocket vehicle 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.[1] Rocket engines work by action and reaction. Rocket engines push rockets forwards simply by throwing their exhaust backwards extremely fast.
Rockets for military and recreational uses date back to at least 13th century China.[2] 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 used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight and space exploration. 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.
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.

History of rockets

History of rockets

In antiquity

Early Chinese rocket.
The availability of black powder (gunpowder) to propel projectiles was a precursor to the development of the first solid rocket. Ninth century Chinese Taoist alchemists discovered black powder while searching for the elixir of life; this accidental discovery led to experiments as weapons such as bombs, cannon, incendiary fire arrows and rocket-propelled fire arrows.[nb 1][nb 2] The discovery of gunpowder was probably the product of centuries of alchemical experimentation.[5]
Exactly when the first flights of rockets occurred is contested. A common claim is that the first recorded use of a rocket in battle was by the Chinese in 1232 against the Mongol hordes at Kai Feng Fu. This is based on an old Mandarin civil service examination question which reads "Is the defense of Kai Feng Fu against the Mongols (1232) the first recorded use of cannon?".[6] Another question from the examinations read "Fire-arms began with the use of rockets in the dynasty of Chou (B. C. 1122-255)--in what book do we first meet with the word p'ao, now used for cannon?".[7]

Forces on a rocket in flight

Forces on a rocket in flight

Forces on a rocket in flight, rockets that must travel through the air are usually tall and thin as this shape gives a high ballistic coefficient and minimizes drag losses
The general study of the forces on a rocket or other spacecraft is part of ballistics and is called astrodynamics.
Flying rockets are primarily affected by the following:[75]
  • Thrust from the engine(s)
  • Gravity from celestial bodies
  • Drag if moving in atmosphere
  • Lift; usually relatively small effect except for rocket-powered aircraft
In addition, the inertia and centrifugal pseudo-force can be significant due to the path of the rocket around the center of a celestial body; when high enough speeds in the right direction and altitude are achieved a stable orbit or escape velocity is obtained.
These forces, with a stabilizing tail (the empennage) present will, unless deliberate control efforts are made, naturally cause the vehicle to follow a roughly parabolic trajectory termed a gravity turn, and this trajectory is often used at least during the initial part of a launch. (This is true even if the rocket engine is mounted at the nose.) Vehicles can thus maintain low or even zero angle of attack which minimizes transverse stress on the launch vehicle; permitting a weaker, and hence lighter, launch vehicle.

Military

Military

Arrow anti-ballistic missile launch
Some military weapons use rockets to propel warheads to their targets. A rocket and its payload together are generally referred to as a missile when the weapon has a guidance system (not all missiles use rocket engines, some use other engines such as jets) or as a rocket if it is unguided. Anti-tank and anti-aircraft missiles use rocket engines to engage targets at high speed at a range of several miles, while intercontinental ballistic missiles can be used to deliver multiple nuclear warheads thousands of miles, and anti-ballistic missiles try to stop them.

Science & research

A Bumper sounding rocket
Sounding rockets are commonly used to carry instruments that take readings from 50 kilometres (31 mi) to 1,500 kilometres (930 mi) above the surface of the Earth, the altitudes between those reachable by weather balloons and satellites.[65]
Rocket engines are also used to propel rocket sleds along a rail at extremely high speed. The world record for this is Mach 8.5.[66]

Spaceflight

Space Shuttle Atlantis during launch phase
Larger rockets are normally launched from a launch pad which serves as stable support until a few seconds after ignition. Due to their high exhaust velocity - 2,500 to 4,500 m/s (9,000 to 16,000 km/h; 5,600 to 10,000 mph) (Mach ~10+), rockets are particularly useful when very high speeds are required, such as orbital speed (Mach 24+[67]). Spacecraft delivered into orbital trajectories become artificial satellites which are used for many commercial purposes. Indeed, rockets remain the only way to launch spacecraft into orbit and beyond.[68] They are also used to rapidly accelerate spacecraft when they change orbits or de-orbit for landing. Also, a rocket may be used to soften a hard parachute landing immediately before touchdown (see retrorocket).

Post World War II

Post World War II

Dornberger and Von Braun after being captured by the Allies
At the end of World War II, competing Russian, British, and US military and scientific crews raced to capture technology and trained personnel from the German rocket program at Peenemünde. Russia and Britain had some success, but the United States benefited the most. The US captured a large number of German rocket scientists (many of whom were members of the Nazi Party, including von Braun) and brought them to the United States as part of Operation Overcast.[44] In America, the same rockets that were designed to rain down on Britain were used instead by scientists as research vehicles for developing the new technology further. The V-2 evolved into the American Redstone rocket, used in the early space program.[45]
After the war, rockets were used to study high-altitude conditions, by radio telemetry of temperature and pressure of the atmosphere, detection of cosmic rays, and further research; notably for the Bell X-1 to break the sound barrier. This continued in the US under von Braun and the others, who were destined to become part of the US scientific community.
R-7 8K72 "Vostok" permanently displayed at the Moscow Trade Fair at Ostankino; the rocket is held in place by its railway carrier, which is mounted on four diagonal beams that constitute the display pedestal. Here the railway carrier has tilted the rocket upright as it would do so into its launch pad structure -- which is missing for this display.
Independently, in the Soviet Union's space program research continued under the leadership of the chief designer Sergei Korolev.[46] With the help of German technicians, the V-2 was duplicated and improved as the R-1, R-2 and R-5 missiles. German designs were abandoned in the late 1940s, and the foreign workers were sent home. A new series of engines built by Glushko and based on inventions of Aleksei Mihailovich Isaev formed the basis of the first ICBM, the R-7.[47]

Modern rocketry

Modern rocketry


Robert Goddard and the first liquid-fueled rocket.
Modern rockets were born when Goddard attached a supersonic (de Laval) nozzle to a liquid-fueled rocket engine's combustion chamber. These nozzles turn the hot gas from the combustion chamber into a cooler, hypersonic, highly directed jet of gas, more than doubling the thrust and raising the engine efficiency from 2% to 64%In 1926, Robert Goddard launched the world's first liquid-fueled rocket in Auburn, Massachusetts.
During the 1920s, a number of rocket research organizations appeared worldwide. In 1927 the German car manufacturer Opel began to research rocket vehicles together with Mark Valier and the solid-fuel rocket builder Friedrich Wilhelm Sander.[35] In 1928, Fritz von Opel drove with a rocket car, the Opel-RAK.1 on the Opel raceway in Rüsselsheim, Germany. In 1928 the Lippisch Ente flew, rocket power was used to launch the manned glider, although it was destroyed on its second flight. In 1929 von Opel started at the Frankfurt-Rebstock airport with the Opel-Sander RAK 1-airplane, which was damaged beyond repair during a hard landing after its first flight.
In the mid-1920s, German scientists had begun experimenting with rockets which used liquid propellants capable of reaching relatively high altitudes and distances. In 1927 and also in Germany, a team of amateur rocket engineers had formed the Verein für Raumschiffahrt (German Rocket Society, or VfR), and in 1931 launched a liquid propellant rocket (using oxygen and gasoline).[36]