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For other uses, see Rocket (disambiguation).
A Redstone rocket, part of the Mercury program
A Redstone rocket, part of the Mercury program

A rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving exhaust gas 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. This distinction generally applies only in the case of weapons, though, and not to civilian or orbital launch vehicles.

In all rockets the exhaust is formed from propellant which is carried within the rocket prior to its release. Rocket thrust is due to accelerating the exhaust gases (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 used to accelerate, change orbits, de-orbit for landing, for the whole landing if there is no atmosphere (e.g. for landing on the Moon), and sometimes to soften a parachute landing immediately before touchdown (see Soyuz spacecraft).

Most current rockets are chemically powered rockets (internal combustion engines). A chemical rocket engine can use solid propellant (see Space Shuttle's SRBs), liquid propellant (see Space shuttle main engine), or a hybrid mixture of both. 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.

Not all rockets use chemical reactions. Steam rockets, for example, release superheated water through a nozzle where it instantly flashes to high velocity steam, propelling the rocket. The efficiency of steam as a rocket propellant is relatively low, but it is simple and reasonably safe, and the propellant is cheap and widely available. Most steam rockets have been used for propelling land-based vehicles but a small steam rocket was tested in 2004 on board the UK-DMC satellite. There are proposals to use steam rockets for interplanetary transport using either nuclear or solar heating as the power source to vaporize water collected from around the solar system.

Rockets where the heat is supplied from other than the propellant, such as steam rockets, are classed as external combustion engines. Other examples of external combustion rocket engines include most designs for nuclear powered rocket engines. Use of hydrogen as the propellant for external combustion engines gives very high velocities.

Due to their high exhaust velocity (mach ~10+), rockets are particularly useful when very high speeds are required, such as orbital speed (mach 25). 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 initial mass to final mass ('mass ratio').

Rockets must be used when there is no other substance (land, water, or air) or force (gravity, magnetism, light) that a vehicle may employ for propulsion, such as in space. In these circumstances, it is necessary to carry all the propellant to be used.

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.

Often, the required velocity (delta-v) for a mission is unattainable by any single rocket because the propellant, structure, guidance and engines weigh so much as to prevent the mass ratio from being high enough. This problem is frequently solved by staging - the rocket sheds excess weight (usually tankage and engines) during launch to reduce its weight and effectively increase its mass ratio.

Typically, the acceleration of a rocket increases with time (even if the thrust stays the same) as the weight of the rocket decreases as fuel is burned. Discontinuities in acceleration will occur when stages burn out, often starting at a lower acceleration with each new stage firing.



Origins of rocketry

Siemenowicz multi-stage rocket, from his Artis Magnae Artilleriae pars prima
Siemenowicz multi-stage rocket, from his Artis Magnae Artilleriae pars prima

The ancient Chinese invention of gunpowder by Taoist chemists, and their use of it in various forms of weapons: (fire arrows), bombs, and cannon, resulted in the development of the rocket. They were initially developed for religious proceedings that were related to the worship and celebration of the Chinese Gods in the ancient Chinese religion. They were the precursors to modern fireworks and, after extensive research, were adapted for use as artillery in warfare during the 10th century to 12th century. Some of the ancient Chinese rockets were stationed at the military fortification known as the Great Wall of China, and employed by the elite soldiers stationed there. Rocket technology first became known to Europeans following their use by the Mongols Genghis Khan and Ogodei Khan when they conquered Russia, Eastern Europe, and parts of Central Europe(i.e. Austria). The Mongolians had stolen the Chinese technology by conquest of the northern part of China and also by the subsequent employment of Chinese rocketry experts as mercenaries for the Mongol military. Additionally, the spread of rockets into Europe was also influenced by the Ottomans at the siege of Constantinople in 1453. Although it is very likely that the Ottomans themselves were influenced by the Mongol invasions of the previous few centuries. Nevertheless, for several more centuries rockets remained misunderstood curiosities to those in the West.

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 contained 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 rods).

At the end of the 18th century, rockets were successfully used militarily in India against the British by Tipu Sultan of the Kingdom of Mysore during the first Mysore War. The British then took an active interest in the technology and developed it 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. At the Battle of Baltimore in 1814, the rockets fired on Fort McHenry by the rocket vessel HMS Erebus were the source of the rockets' red glare described by Francis Scott Key in The Star-Spangled Banner.

Early rockets were very inaccurate. Without the use of spinning or any gimballing of the thrust, they had a strong tendency to veer sharply off course. The early British Congreve rockets reduced this 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.

Robert Goddard and his first liquid-fueled rocket
Robert Goddard and his first liquid-fueled rocket

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.


Under international law, the nationality of the owner of a launch vehicle determines which country is responsible for any damages resulting from that vehicle. Due to this, some countries require that rocket manufacturers and launchers adhere to specific regulations to indemnify and protect the safety of people and property that may be affected by a flight.

In the US any rocket launch that is not classified as amateur, and also is not "for and by the government," must be approved by the Federal Aviation Administration's Office of Commercial Space Transportation (FAA/AST), located in Washington, DC.


Because of the power and sensitivity of fuels used by rockets, accidents can and have happened. The number of people injured or killed is usually small because of the great care given to the volatility of the materials, but this record is not perfect.

See List of space disasters


  • Nuclear thermal rockets have also been developed, but never deployed, they are particularly promising for interplanetary use because of their high efficiency.
  • Neofuel - Nuclear/solar steam rockets for interplanetary use, using abundant extraterrestrial ice.
  • 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

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