Rocket

A rocket (from Italian: rocchetto, lit. ''bobbin/spool'', and so named for its shape) is an elongated flying vehicle that uses a rocket engine to accelerate without using any surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Unlike jet engines, rockets are fuelled entirely by propellant which they carry, without the need for oxygen from air; consequently a rocket can fly in the vacuum of space, indeed rocket engines operate more efficiently outside the atmosphere.

Multistage rockets are capable of attaining escape velocity from Earth and therefore can achieve unlimited maximum altitude. Compared with airbreathing engines, rockets are lightweight and powerful and capable of generating large accelerations.

Rockets for military and recreational uses date back to at least 13th-century China. Significant scientific, interplanetary and industrial use did not occur until the 20th century, when rocketry was the enabling technology for the Space Age, including setting foot on the Moon. Rockets are now used for fireworks, missiles and other weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight, and space exploration.

History

Main article: History of rockets

Further information: Timeline of rocket and missile technology

Gunpowder-powered rockets began in medieval China during the Song dynasty by the 13th century. These early rockets were used in military exercises and battles. The idea of rockets spread to other parts of the world through invasions and trade.

Later, rockets were used in wars and sieges as tools to set fires. Over time, people in different countries improved rocket designs. By the 18th century, India developed strong iron-cased rockets, which were later used and improved by the British. These advances helped rockets travel much farther in battles.

In the 20th century, scientists began thinking about using rockets to travel to space. Important developments happened in Germany, the United States, and the Soviet Union. By the mid-1900s, rockets were used not just for war but also to explore space. This led to amazing achievements, such as the first human landing on the Moon in 1969, made possible by powerful rockets like the Saturn V.

Types

Rocket vehicles come in many shapes and sizes. Some are small and fun, like tiny balloon rockets, water rockets, or skyrockets you can buy at a hobby store. Others are very large and powerful, like the Saturn V space rocket used for the Apollo program.

There are also special rockets such as missiles, rocket cars, rocket-powered aircraft, rocket sleds, and even space probes. Some rockets help people escape danger quickly, like ejection seats in airplanes.

Design

A rocket design can be simple, like a cardboard tube filled with black powder, but making an efficient rocket involves solving many challenges. These include keeping the fuel cool, moving the fuel to the engine, and controlling the rocket's direction.

Rockets have several key parts. They need fuel, a place to store that fuel (like a propellant tank), and a nozzle. They might also have rocket engines, parts to help them stay steady (fins, gyroscopes), and a strong structure to hold everything together. Some rockets have extra parts like wings, parachutes, or even a person in a rocket belt.

Rocket engines work by pushing out hot gas at high speed. This creates a force that moves the rocket forward. Rockets can use different kinds of fuel, such as solid propellant or liquid propellant, and some even use hot water or steam to move. The fuel burns in a special chamber, and the resulting gases shoot out the back, which pushes the rocket forward.

Uses

Rockets are special vehicles that carry their own fuel to move, which makes them useful in places where there is no air, like space. They are needed when there is nothing else around—like land, water, or air—to help a vehicle move.

Rockets are used in many ways. In the military, they help send weapons to targets far away. For science, small rockets called sounding rockets carry instruments high above Earth to collect information. The first pictures of Earth from space were taken by a rocket in 1946.

Larger rockets are used to launch spacecraft into orbit around Earth or to send them to other parts of space. They are the only way to get spacecraft into orbit. Rockets are also used in hobbies, like model rocketry, where people build and launch small rockets for fun and learning. These rockets can be made from simple materials and are a safe and inspiring activity for many young people.

Flight

Launches for orbital spaceflights or into interplanetary space usually start from a fixed place on the ground, but they can also begin from an airplane or ship.

Rocket launch technologies include all the systems needed to successfully launch a vehicle. This includes not just the rocket itself, but also the control systems, mission control centre, launch pad, ground stations, and tracking stations. These are often called the "ground segment".

Most rockets take off straight up and then slowly lean over, following a path called a gravity turn. Once high enough, the rocket points mostly sideways to keep rising while speeding forward. As it speeds up, it becomes more and more horizontal until it reaches the right speed for orbit, and then the engine stops.

Current rockets "stage," meaning they drop parts as they go up. While some ideas exist for rockets that don’t need to drop parts, none have been built yet. Most dropped parts fall back into the ocean, but some have been caught again using parachutes or special landings.

When sending a spacecraft into orbit, sometimes the rocket needs to turn a bit during its climb. This turn, called a "dogleg," helps avoid flying over land or areas with many people, or to reach the right path for orbit. Doglegs need extra fuel and can make the flight a bit harder.

Noise

Rocket engines create very loud sounds when they shoot out gas at high speed. These sounds can be strong enough to hurt people nearby. For example, the Space Shuttle made a noise level of 180 dB, which is extremely loud. To protect the rocket and its crew, scientists used a special water system to lower the noise to a safer level.

The loudest noises happen when the rocket is close to the ground. To make it quieter, engineers use tricks like special trenches and water to help reduce the sound. For astronauts inside the rocket, they are placed far away from the engines to keep them safe from the loud noises. When a rocket goes faster than the speed of sound, the sound fades away because the rocket is moving too quickly for the sound to catch up.

Physics

Operation

The burning of fuel in a rocket engine increases the energy of the gases, using the stored energy in the fuel. As this energy increases, pressure builds up, and a special part called a nozzle turns this energy into movement. This movement creates a force that pushes the rocket forward.

When gases are at the top of the engine, they cannot move forward, so they push against the engine, helping to lift the rocket. As the gases move toward the end of the engine, they speed up. A special shape in the engine helps these gases speed up even more. The faster the gases move, the less pressure there is. When the gases leave the engine, they push against it, which helps the rocket move forward. This is because every action has an equal and opposite reaction.

Forces on a rocket in flight

Flying rockets feel several forces:

• Thrust from the engine
• Gravity from planets or stars
• Drag if moving through air
• Lift; this is usually small except for special rockets that can fly like airplanes

Other forces, like the rocket’s path around a planet, can also affect it. These forces make the rocket follow a curved path called a gravity turn, which helps during the early part of a flight.

Drag

Drag is a force that goes against the rocket’s motion through air. It slows the rocket down and can put pressure on it. Drag can be reduced by shaping the rocket with a pointed nose and keeping it slim. During launch, there is a point where drag is the strongest, called max Q. At this point, the rocket must be strong enough to handle the pressure.

Net thrust

Rocket engines can burn a lot of fuel very quickly, creating strong thrust. The thrust can be changed during flight to control the rocket’s speed and manage forces on it.

Total impulse

Impulse measures how much a force changes an object’s motion over time. For rockets, it shows how well they can change their speed and carry weight.

Specific impulse

Specific impulse tells us how well a rocket uses its fuel. It is important because it shows how much thrust a rocket can create from its fuel.

Delta-v (rocket equation)

Delta-v is how much a rocket’s speed can change without outside help. It can be calculated using a special formula. For example, launching from Earth to orbit needs about 9.7 km/s of delta-v.

Mass ratios

Most of a rocket’s weight is fuel. A high mass ratio means the rocket is light and performs better. Liquid rockets often have the highest mass ratios.

Staging

Because it’s hard for one rocket to reach space, rockets often have stages. When a stage finishes burning, it falls away, making the rocket lighter. This helps the rocket go faster and farther.

Acceleration and thrust-to-weight ratio

Rockets can speed up very quickly because they are very light once they start burning fuel. This quick speed-up is called acceleration. Some rockets can even take off and land straight up because of this.

Energy

Energy efficiency

Rocket fuel has less energy than regular airplane fuel, but rockets are good when very high speeds are needed, like for space travel. Rockets are not usually used for regular airplanes because they need much more fuel to go the same distance.

Oberth effect

When a rocket is already moving fast, burning fuel at that moment makes it gain more speed than if it burned the same fuel when it was slower. This is important for space travel.

Safety, reliability and accidents

Rockets are built with great care to ensure they work safely. However, because they hold a lot of powerful fuel, problems can sometimes lead to serious outcomes. For example, during a test before a flight in 1967, a fire happened on the Apollo I spacecraft, which was very sad. Later, in 1986, the Space Shuttle Challenger had an accident during launch. Scientists and engineers work hard to make sure these kinds of incidents do not happen again and to keep improving the safety of space travel.

Costs and economics

The cost of building a rocket can be broken down into three main parts: the fuel needed to make it fly, the weight of the rocket itself without fuel, and the cost of equipment and places used for launching.

Most of the weight of a rocket when it takes off is fuel. Even though fuel is not extremely expensive, it still adds up because rockets need a lot of it to reach space. The rest of the rocket’s weight is made up of the rocket itself, and this part usually costs more than the fuel. Making sure a rocket works safely and can fly to space is very important, which also adds to the cost.

In recent years, private companies have started offering space flights, which has helped make space travel more affordable.