Rocket

For other uses, see Rocket (disambiguation). Not to be confused with Launch vehicle.

A rocket (from Italian: rocchetto, meaning "bobbin" or "spool," and named for its shape) is a long vehicle that flies using a rocket engine to accelerate. It does not need any air around it to fly. A rocket engine makes thrust by pushing out hot gas, called exhaust, at high speed. Unlike jet engines, rockets carry all of their fuel, called propellant, and they do not need oxygen from the air. This means a rocket can fly through the vacuum of space. Rocket engines actually work better outside the air.

Multistage rockets can reach escape velocity from Earth, so they can, in theory, go up very high. Compared with airbreathing engines, rockets are light and powerful. They can speed up quickly. To steer, rockets may use airfoils, auxiliary reaction engines, gimballed thrust, momentum wheels, deflection of the exhaust stream, changes in propellant flow, and spin. Some rockets simply fly in a ballistic trajectory, moving through the air as gravity pulls them.

Rockets for military and fun uses date back to at least the 13th century in China. Rockets were not used for important science, space, and industry until the 20th century. Rockets made the Space Age possible, including setting foot on the Moon. Today, rockets are used for fireworks, missiles and other weapons, ejection seats, launch vehicles that carry artificial satellites, human spaceflight, and space exploration.

Chemical rockets are the most common type of powerful rocket. They usually make hot exhaust by burning fuel with an oxidizer. Their propellant can be a simple pressurized gas. It can be a single liquid fuel that breaks apart when a catalyst is present (monopropellant). It can also be two liquids that react when they touch (hypergolic propellants). Or it can be two liquids that must be lit to react, like kerosene (RP1) and liquid oxygen. These are used in most liquid-propellant rockets. Other options include a solid mix of fuel and oxidizer (solid fuel), or solid fuel with a liquid or gas oxidizer (hybrid propellant system). Chemical rockets store a lot of energy that is easy to release, so if something goes wrong, the results can be serious.

The word "rocket" is also used for small fireworks. These are the subject of the article rocket (firework).

History

Main article: History of rockets

Further information: Timeline of rocket and missile technology

Gunpowder-powered rockets were made in medieval China under the Song dynasty by the 1200s. An early multiple rocket launcher was made then too. The Mongol invasions spread the idea to the Middle East and Europe in the mid-1200s. A military exercise from 1245 used rockets. In 1264, a firework called the "ground-rat" frightened Empress-Mother Gongsheng at a feast held by her son, Emperor Lizong. The military book Huolongjing, also called the Fire Drake Manual, was written by Jiao Yu in the mid-1300s. It describes the first known multistage rocket, the 'fire-dragon issuing from the water'. Medieval rockets were used as incendiary weapons in sieges. Hasan al-Rammah wrote about gunpowder recipes, including 22 for rockets. Roger Bacon mentioned firecrackers in the Opus Majus of 1267. The Liber Ignium (Book of Fire) gave instructions for similar devices. Konrad Kyeser described rockets in Bellifortis around 1405. In 1420, Giovanni Fontana, a Paduan engineer, created rocket-propelled animal figures. The name "rocket" comes from the Italian rocchetta, meaning "bobbin", because of its shape. Leonhard Fronsperger and Conrad Haas brought the word into German, and "rocket" appeared in English by the early 1600s. Artis Magnae Artilleriae pars prima, an important book on rocket artillery by Casimir Siemienowicz, was printed in Amsterdam in 1650.

The Mysorean rockets were the first successful iron-cased rockets. They were made in the late 1700s in the Kingdom of Mysore, now part of India, under Hyder Ali. The Congreve rocket, a British weapon designed by Sir William Congreve in 1804, was based on them. It was used in the Napoleonic Wars. Francis Scott Key wrote about the "rockets' red glare" in 1814, when he was held on a British ship that was attacking Fort McHenry. William Moore gave the first mathematical study of rocket propulsion in 1813. In 1815, Alexander Dmitrievich Zasyadko built launch platforms that could fire salvos of six rockets at once. William Hale greatly improved rocket accuracy in 1844. Edward Mounier Boxer further improved the Congreve rocket in 1865. In 1861, William Leitch first suggested using rockets for human spaceflight. Konstantin Tsiolkovsky later developed the idea in 1903. During World War I, the British Royal Flying Corps designed a guided rocket. Archibald Low described an electrically steered rocket built by the Experimental Works in 1917. Rocket experiments were done with Cdr. Brock. In 1920, Robert Goddard of Clark University published ideas for better rockets in A Method of Reaching Extreme Altitudes. In 1923, Hermann Oberth published Die Rakete zu den Planetenräumen. In 1926, Goddard added a supersonic (de Laval) nozzle to a high-pressure combustion chamber. This made a faster, more focused jet of gas, which made modern rockets possible. He also used liquid propellants instead of gunpowder, which made rockets much lighter and more effective.

In 1921, the Soviet Gas Dynamics Laboratory began developing solid-propellant rockets. In 1931, these were used for the first successful jet-assisted takeoff of aircraft. They became the models for the Katyusha rocket launcher used in World War II. In 1929, Fritz Lang's science fiction film Woman in the Moon showed a multi-stage rocket. It also introduced the idea of a rocket launch pad and a rocket-launch countdown. In 1943, production of the V-2 rocket began in Germany. It was designed by the Peenemünde Army Research Center, with Wernher von Braun as technical director. On 20 June 1944, a V-2 launched straight up as MW 18014. It became the first artificial object to cross the Kármán line into space. Rockets were also used on aircraft in Germany, including for RATO, the Bachem Ba 349 "Natter", and the Me 163. The Allies mostly used unguided rockets, such as the Soviet Katyusha and the American bazooka. In 1945, the Americans brought many German rocket scientists, including von Braun, to the United States through Operation Paperclip. After the war, rockets were used to study the upper atmosphere. In 1947, the Bell X-1 became the first crewed vehicle to break the sound barrier. In the Soviet Union's space program, work continued under the leadership of chief designer Sergei Korolev. During the Cold War, rockets became very important for the military, with the development of intercontinental ballistic missiles. In the 1960s, rockets advanced quickly. The Soviet Union built Vostok, Soyuz, and Proton, and the United States built the X-15. Rockets were used for space exploration. American crewed programs, Project Mercury, Project Gemini, and the Apollo programme, reached their peak in 1969. That year, the first crewed landing on the Moon took place, using equipment launched by the Saturn V rocket.

Types

Rockets are often built in the tall, thin shape that most people picture, which takes off straight up. But there are many different types of rockets. Small ones include balloon rockets, water rockets, skyrockets and small solid rockets, which you can buy at a hobby store. Other types include missiles, space rockets such as the huge Saturn V used for the Apollo program, rocket cars and a rocket bike.

Rockets also power many other kinds of vehicles and machines. These include rocket-powered aircraft (including rocket-assisted takeoff of regular aircraft – RATO), rocket sleds, rocket trains, rocket torpedoes and rocket-powered jet packs. Rapid escape systems such as ejection seats and launch escape systems are also types of rockets, and so are space probes.

Design

A rocket can be as simple as a cardboard tube filled with black powder. Building a rocket that flies well and goes where it should takes careful work. The main challenges are keeping the engine cool, moving fuel when it is a liquid, and steering the rocket in the right direction. A rocket needs a propellant, a place to store it such as a propellant tank, and a nozzle. Many rockets also have rocket engines and parts to keep them steady, such as fins, vernier engines, engine gimbals for thrust vectoring, and gyroscopes. Most rockets also have a frame, usually a monocoque, that holds everything together. Rockets built for fast flight through air often have a smooth nose cone that usually carries the payload. Some rockets add wings (rocketplanes), parachutes, wheels (rocket cars), or even a person in a rocket belt. Many rockets also have guidance systems that use satellite navigation and inertial navigation systems.

Rocket engines work by jet propulsion. Most rockets today are powered by chemical reactions, usually in internal combustion engines, and they send out hot exhaust gas. Engines can use solid propellant, liquid propellant, or a mixture of both. Some rockets use heat or pressure from sources other than a chemical reaction, such as steam rockets, solar thermal rockets, or water rocket and cold gas thrusters. In combustion engines, fuel and an oxidizer react in the combustion chamber. The hot gases rush out of a rocket engine nozzle at the back of the rocket. This acceleration pushes against the chamber and nozzle, which moves the rocket forward. This is explained by Newton's third law. The shape of the nozzle also points the exhaust along the rocket's axis.

Rocket propellant is the material stored in a tank or casing until it is pushed out of the engine as a fluid jet that creates thrust. Chemical rockets often burn a fuel such as liquid hydrogen or kerosene with an oxidizer such as liquid oxygen or nitric acid. This makes large amounts of very hot gas. Some propellants, called monopropellants, break down into hot gas without burning. Examples include hydrazine, nitrous oxide, and hydrogen peroxide. Other rockets heat an inert propellant from outside, as in steam, solar thermal, or nuclear thermal rockets. Small rockets, such as attitude control thrusters, use pressurized fluid that escapes through a nozzle.

The first liquid-fuel rocket, built by Robert H. Goddard, was very different from modern rockets. Its engine was at the top and its fuel tank was at the bottom. Goddard believed it would stay steady by "hanging" from the engine like a pendulum. However, it veered off course and crashed 184 feet (56 m) from the launch site. This showed it was no more stable than a rocket with its engine at the bottom.

Uses

Rockets are needed when there is nothing a vehicle can push against to move, such as in space. Rockets are reaction devices that carry their own propellant. This means all of the propellant must be carried along. Rockets are also useful in many other situations, but they do not need gravity, magnetism, or light to work.

Some military weapons use rockets to carry warheads to their targets. Weapons with a guidance system are called missiles. Unguided ones are called rockets. Anti-aircraft missiles and anti-tank missiles use rocket engines to reach their targets quickly. Intercontinental ballistic missiles can carry nuclear warheads over very long distances. Anti-ballistic missiles are designed to stop them. Rockets have also been tested for reconnaissance, such as the Ping-Pong rocket, but they have never been widely used by militaries.

See also: Space probe

Sounding rockets carry instruments that measure conditions high above the Earth. The first images of Earth from space were taken from a V-2 rocket in 1946 (flight #13). Rocket engines are also used to move rocket sleds along a rail at very high speed.

Main article: Spaceflight

Large rockets usually launch from a launch pad. Rockets are especially useful when very high speeds are needed, such as orbital speed. Rockets are still the only way to launch spacecraft into orbit and beyond. They are also used to change orbits or to slow down for landing. A retrorocket can soften a parachute landing just before touching the ground.

Rockets have been used to fire a line to a ship in trouble. This lets a Breeches buoy help rescue people on board. Rockets are also used to launch emergency flares. Some crewed rockets, such as the Saturn V and Soyuz, have launch escape systems that can pull the crew capsule away to safety. Many military aircraft use solid rocket powered ejection seats to move crew to safety when the aircraft cannot be controlled.

Main article: Model rocket

A model rocket is a small rocket made to fly to low heights and be recovered in different ways. Model rockets are often made of paper, wood, plastic, and other light materials. The National Association of Rocketry has a safety code for them. Hobbyists build many kinds of model rockets. Some use water rockets, which use water as their reaction mass. Rockets are also used in some fireworks. Hydrogen peroxide rockets power jet packs and have been used to power cars. A rocket car also holds an unofficial drag racing record.

Flight

Rockets that travel into orbital spaceflights or into interplanetary space usually take off from a fixed place on the ground. They could also launch from an aircraft or a ship. A launch needs more than just the rocket. It also needs firing controls, a mission control centre, a launch pad, ground stations, and tracking stations. These are often called the "ground segment."

Rockets that go into orbit usually rise straight up. Then they slowly tilt over, often following a path called a gravity turn. Once they are above most of the air, they point the engine mostly sideways and a little downward. This helps them gain speed and stay high. When they reach orbital speed, the engine shuts off.

Every rocket in use today drops parts on the way to orbit. This is called staging. Some people have proposed rockets that could reach orbit without staging, but none have been built. The exponentially increasing fuel requirements would leave little or no room for useful cargo. Most rockets let the dropped parts fall into the ocean, but some have been recovered and reused.

When a rocket launches a spacecraft into orbit, it may make a "dogleg." This is a guided, powered turn during the climb that bends its path away from a straight line. A dogleg may be needed if the chosen direction would take the ground track over land or over populated areas. It may also be needed if the rocket must reach an orbit that does not pass over the latitude of the launch site. Doglegs are not preferred because they need extra fuel. That extra fuel makes the rocket heavier and lowers how well it performs.

Noise

Rocket exhaust makes a lot of noise. When supersonic exhaust hits the air around it, shock waves form. How loud these waves are depends on the rocket's size and how fast the exhaust moves. Very large, powerful rockets can be dangerous to people standing close by.

The Space Shuttle made 180 dB of noise around its base. NASA built a sound suppression system that pours water onto the launch pad. This lowered the noise to 142 dB. Without it, sound would bounce off the pad back toward the rocket and could damage it. The noise is strongest when a rocket is near the ground. On crewed rockets, astronauts sit far from the engines to keep them safer. Once a vehicle goes supersonic, the sound stops being felt by the people inside, because the sound waves can no longer keep up.

Physics

A rocket engine burns fuel. This heats the gases inside and creates pressure. A nozzle turns that pressure into fast-moving gas that shoots out the back. The gas pushes against the rocket, so the rocket moves in the opposite direction, as explained by Newton's third law. Rockets carry their own propellant, so they do not need air and can fly in space. Their engines also work better outside the atmosphere. How fast the exhaust leaves the rocket matters a lot, and engineers measure this with specific impulse.

Several forces act on a rocket in flight. These include thrust from the engine, gravity, drag from moving through air, and lift. Rockets often follow a curved path called a gravity turn during launch. A long, thin shape and a smooth nose help reduce drag. Most of a rocket's weight is propellant. Rockets are very powerful for their weight, but they waste much of their energy at low speeds. For this reason, they are mainly used when very high speeds are needed, such as launching into orbit. Many large rockets are built in stages, dropping empty parts during flight to save weight.

Costs and economics

The costs of rockets can be split into three parts: fuel (propellant), the rocket's non-fuel parts, and the support equipment and facilities. Most of a rocket's takeoff weight is usually fuel. Still, fuel is rarely more than a few times as expensive as gasoline per kilogram. For most rockets, fuel costs are small compared with other costs, though not zero. In 2009, the Space Shuttle used about $1.4 million in fuel for each launch, while its other expenses were about $450 million. Some of its fuel was liquid, held in the external fuel tank, and some was solid, held in the SRBs.

A rocket's non-fuel parts are often only 5–20% of its total mass, but they make up most of the cost. For rockets that reach orbit, these parts often cost $2,000 to $10,000 or more per kilogram. Most of that money goes to engineering, building, and testing. Rockets that reach orbit must be carefully checked to make sure they work reliably, which adds to the cost. Costs can be lowered by building many simple rockets, by making reusable rockets that fly often, or by using a non-rocket spacelaunch system for part of the trip to orbit. Support equipment, launch pads, and range costs grow with the size of the rocket, but they change little with how often it launches. Rockets used for other purposes, such as military rockets and rocket-assisted take off, often do not need the same performance, so they are usually cheaper.

Further information: Space launch market competition § 2010s: Competition and pricing pressure

Since the early 2010s, new private options for spaceflight services have appeared. They have put strong price pressure on the existing market.