Online Encyclopedia
Rocket
- 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 fast moving exhaust from within a rocket engine. 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.
A missile, by contrast, can use either solid or liquid propellant, and has a guidance system.
In all rockets the exhaust is formed from propellant which is carried within the rocket prior to its release. Rocket thrust is due to the exhaust gases applying pressure on the inside surfaces of the rocket engine as they accelerate (see Newton's 3rd Law of Motion).
There are many different types of rockets, and a comprehensive list can be found in spacecraft propulsion- they range in size from tiny models that can be purchased at a hobby store, to the enormous Saturn V used for the Apollo program.
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 (with the rocket engines classed as internal combustion engines). 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.
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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.
Since mid-17th century, for over two centuries the work of Polish-Lithuanian Commonwealth nobleman Kazimierz Siemienowicz, "Artis Magnae Artilleriae pars prima" ("Great Art of Artillery, the First Part". also known as "The Complete Art of Artillery"), was used in Europe as a basic artillery manual. The book provided the standard designs for creating rockets, fireballs, and other pyrotechnic devices. It contains a large chapter on caliber, construction, production and properties of rockets (for both military and civil purposes), including multi-stage rockets, batteries of rockets, and rockets with delta wing stabilizers (instead of the common guiding rod s).
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 launch
- Rocket sled
- Skyrocket
- Spacecraft propulsion
- Stalin Organ
- Water rocket
- Tsiolkovsky rocket equation
External Links:
Governing Agencies
- NASA http://www.nasa.gov
- National Association of Rocketry http://www.nar.org
- Hobby Industry Association http://www.hobby.org
- Radio Control Hobby Trade Association http://www.rchta.org
- Canadian Association of Rocketry http://www.canadianrocketry.org
- Japan Association of Rocketry (site in Japanese) http://www.ja-r.net
Software
- SpaceCAD http://www.spacecad.com
- RockSIM http://www.apogeerockets.com/rocksim.asp
Manufacturers and Part Suppliers
- Estes Industries http://www.estesrockets.com
- LOC Precision http://www.locprecision.com
- Apogee Components, Inc. http://www.apogeerockets.com
- Loki Research, LLC http://www.lokiresearch.com
- Missile Works http://www.missileworks.com
- Squirrel Works http://www.squirrel-works.com
- AeroTech Rocketry http://www.aerotech-rocketry.com
- Magnum, Inc. http://magnumrockets.com
- Fat Cat Rockets, Inc. http://www.fatcatrockets.com
- Advanced Rocketry Corporation http://www.advancedrocketry.com
- Aerocon Systems http://www.aeroconsystems.com
- Aerospace Specialty Products http://www.asp-rocketry.com
- Discount Rocketry http://www.discountrocketry.com
- Giant Leap Rocketry http://www.giantleaprocketry.com
- Top Flight Recovery, LLC http://www.topflightrecoveryllc.com
- U.S. Rockets http://www.usrockets.com
- Polecat Aerospace http://www.polecataerospace.com
- Tango Papa Decals http://www.tangopapadecals.com
- Countdown Hobbies http://www.countdownhobbies.com
- Flis Kits, Inc. http://www.fliskits.com
- B2 Rocketry Company http://www.b2rocketry.com
- Great Lakes Hobbies http://www.greatlakeshobbies.com
Other
- Encyclopedia Astronautica - Rocket and Missile Alphabetical Index http://www.astronautix.com/lvs/
- Gunter's Space Page - Complete Rocket and Missile Lists http://space.skyrocket.de
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There's also an album called Rocket that was released in 1996 by an alternative rock group Primitive Radio Gods.