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:''For rocket lettuce, see
arugula; for the early steam locomotive, see
Stephenson's Rocket, for the sugar candy, see
Rockets.''
A '''rocket''' is a
vehicle,
missile or
aircraft which obtains
thrust by the
reaction to the ejection of a fast moving
exhaust from within a
rocket engine. The exhaust is formed from
propellant which is carried within the rocket prior to its release. The thrust is due to
Newton's 3rd Law of Motion. Often the term '''rocket''' is also used to mean a
rocket engine.
In military terminology, '''a rocket''' generally uses solid propellant and is unguided. These rockets can be fired by ground-attack
aircraft at fixed targets such as buildings, or can be launched by ground forces at other ground targets. During the Vietnam era, there were also air launched unguided rockets that carried a nuclear payload designed to attack aircraft formations in flight.
In military terminology, a
missile, by contrast, can use either solid or liquid propellant, and has a
guidance system.
Rockets range in size from tiny
models that can be purchased at a
hobby store, to the enormous
Saturn V used for the
Apollo program.
There are many different types of rockets, and a comprehensive list can be found in
spacecraft propulsion.
Rockets are also used for deceleration, to transfer to a lower-energy orbit, for example to enter into a circular orbit from outside, to de-orbit for
landing, for the whole landing if there is no atmosphere (e.g. for landing on the
Moon, the rocket of the descent stage of the
Apollo Lunar Module was applied), and sometimes to soften a parachute landing.
Most current rockets are chemical rockets. A chemical
rocket engine may use solid propellant, such as the
Space Shuttle's SRBs, or liquid propellant, like the
Space Shuttle's main engines, or a hybrid. A chemical reaction is initiated between the
fuel and the
oxidizer in the
combustion chamber, and the resultant hot gases accelerate out of a
nozzle (or nozzles) at the rearward facing end of the rocket. The acceleration of these gases through the engine exerts force ('thrust') on the combustion chamber and nozzle, propelling the vehicle (in accordance with Newton's Third Law). See
rocket engine for details.
Rockets must be used when there is no other substance (land, water, or air) that a
vehicle may push against, such as in space. In these circumstances, it is necessary to carry all the
propellant within the vehicle.
Rockets are particularly useful when very high speeds are required, such as orbital speed (mach 25 or so). The speeds that a rocket vehicle can reach can be calculated by the
rocket equation; which gives the speed difference ('
delta-v') in terms of the exhaust speed and ratio of inital mass to final mass ('mass ratio').
Common mass ratios for vehicles are 20/1 for dense propellants such as liquid oxygen and kerosene, 25/1 for dense monopropellants such as hydrogen peroxide, and 10/1 for liquid oxygen and liquid hydrogen. However, mass ratio is highly dependent on many factors such as the type of engine the vehicle uses and structural safety margins.
Sometimes, particularly in launch scenarios, the required velocity (delta-v) for a mission is unattainable because the
propellant, structure,
guidance and engines weigh so much as prevent the mass ratio from being high enough. This problem is frequently solved by
staging - the rocket sheds excess weight (usually tankage and engines) to attain a higher effective mass ratio thus permitting a higher delta-v.
Typically the acceleration of a rocket increases with time due to applying the same thrust to a decreasing mass, with discontinuities when stages burn out, and starting at a lower acceleration with the new stage firing.
== History ==
Historically, rockets were first developed by the
Chinese as early as B.C. 300, using
gunpowder. These were initially developed for entertainment, the precursors to modern
fireworks, but were later adapted for warfare in the
11th century. Because the pressures on the rocket walls are lower, the use of rockets in warfare preceded the use of the gun, which required a higher level of metal technology. It was in this role that rockets first became known to Europeans following their use by
Ottomans at the siege of
Constantinople in
1453. For several more centuries they remained curiosities to those in the West.
At the end of the 18th century, rockets were used militarily in
India against the British by the Mahrattas. The British then took up the practice and developed them further during the 19th century. The major figure in the field at this time was
William Congreve. From there, the use of military rockets spread throughout Europe. The ''rockets' red glare'' helped to inspire the
US national anthem.
Early rockets were highly inaccurate. Without any spinning up of the rocket, nor any
gimballing of the thrust, they had a strong tendency to veer sharply off course. The early British Congreve rockets reduced this tendency somewhat by attaching a long stick to the end of a rocket (similar to modern bottle rockets) to make it harder for the rocket to change course. The largest of the Congreve rockets was the 32 pound (14.5 kg) Carcass, which had a 15 foot (4.6 m) stick. Originally, sticks were mounted on the side, but this was later changed to mounting in the center of the rocket, reducing drag and enabling the rocket to be more accurately fired from a segment of pipe.
The accuracy problem was mostly solved in 1844 when
William Hale modified the rocket design so that thrust was slightly
vectored to cause the rocket to spin along its axis of travel like a bullet. The Hale rocket removed the need for a rocket stick, travelled further due to reduced air resistance, and was far more accurate.
Early rockets were also remarkably inefficient. Modern rockets were born when, after receiving a grant in 1917 from the
Smithsonian Institution,
Robert Goddard attached a
de Laval nozzle to a rocket engine's combustion chamber, doubling the thrust and enormously raising the efficiency, giving the real possibility of practical space travel.
This technique was soon used on the
V-2 rockets, designed by
Wernher Von Braun who became one of the principal players in modern rocket development. V2s were deployed extensively by
Adolf Hitler in the latter stages of
World War II as terror weapons against the
British population, each successful launch reaching high up into the vacuum of space and auguring the beginning of the
Space Age.
Rockets remain a popular military weapon. The use of large battlefield rockets of the V-2 type has given way to guided
missiles, but rockets are often used by
helicopters and light aircraft for ground attack, being more powerful than
machine guns, but without the recoil of heavy
cannon. In the
1950s there was a brief vogue for air-to-air rockets, including the formidable
AIR-2 'Genie'
nuclear rocket, but by the early
1960s these had largely been abandoned in favor of
air-to-air missiles.
== Future ==
Nuclear thermal rockets have also been developed, but never deployed, they are particularly promising for interplanetary use.
Nuclear pulse propulsion rocket concepts give very high thrust and exhaust velocities.
Another class of rocket-like thrusters in increasingly common use are
ion drives, which use electrical rather than chemical energy to accelerate their reaction mass.
==See also==
*
Timeline of rocket and missile technology
*
List of rockets
*
Model rocket
*
Pulse jet engine
*
Rocket fuel
*
Rocket sled
*
Skyrocket
*
Spacecraft propulsion
*
Stalin Organ
*
Water rocket
*
Tsiolkovsky rocket equation
== External Links: ==
Governing Agencies
*
NASA
*
National Association of Rocketry
*
Hobby Industry Association
*
Radio Control Hobby Trade Association
*
Canadian Association of Rocketry
*
Japan Association of Rocketry (site in Japanese)
Software
*
SpaceCAD
*
RockSIM
Manufacturers and Part Suppliers
*
Estes Industries
*
LOC Precision
*
Apogee Components, Inc.
*
Loki Research, LLC
*
Missile Works
*
Squirrel Works
*
AeroTech Rocketry
*
Magnum, Inc.
*
Fat Cat Rockets, Inc.
*
Advanced Rocketry Corporation
*
Aerocon Systems
*
Aerospace Specialty Products
*
Discount Rocketry
*
Giant Leap Rocketry
*
Top Flight Recovery, LLC
*
U.S. Rockets
*
Polecat Aerospace
*
Tango Papa Decals
*
Countdown Hobbies
*
Flis Kits, Inc.
*
B2 Rocketry Company
*
Great Lakes Hobbies
Other
*
Encyclopedia Astronautica - Rocket and Missile Alphabetical Index
*
Gunter's Space Page - Complete Rocket and Missile Lists
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da:Raket
de:Rakete
es:Cohete
fr:Fuse
id:Roket
ms:Roket
nl:Raket
ja:ロケット
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fi:Raketti
sv:Raket
zh-cn:火箭
