Rocket

A rocket (from Italian: rocchetto, lit. ''bobbin/spool'', and so named for its shape) is a long, flying vehicle that uses a rocket engine to accelerate without needing air. A rocket engine creates force by sending out exhaust very fast. Unlike jet engines, rockets carry all their own fuel, so they can fly in the vacuum of space. In fact, rocket engines work better outside the atmosphere.

Multistage rockets can reach escape velocity from Earth and can go very high. Compared with airbreathing engines, rockets are light and strong and can create big accelerations.

Rockets have been used for fun and for serious things since the 1300s in China. They became very important in the 1900s, helping start the Space Age, including setting foot on the Moon. Today, rockets are used for fireworks, 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 started in China long ago during the Song dynasty. People used these early rockets in battles. The idea of rockets traveled to other places through trade and war.

Later, rockets helped start fires in sieges. Over time, many countries made better rockets. By the 1700s, India made strong rockets from iron. The British used and improved these rockets.

In the 1900s, scientists dreamed of using rockets to go to space. Big steps happened in Germany, the United States, and the Soviet Union. Rockets went from tools of war to tools for space. This helped humans do amazing things, like landing on the Moon in 1969, thanks to 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, but making a good rocket is tricky. It needs to keep the fuel cool, move the fuel to the engine, and control the direction.

Rockets have important parts. They need fuel, a place to store it (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. The fuel burns in a special chamber, and the gases shoot out the back, pushing the rocket forward.

Uses

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

Rockets are used in many ways. 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. They can also begin from an airplane or ship.

Rocket launch technologies include all the systems needed to successfully launch a vehicle. This includes the rocket itself, 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. They follow 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. Then the engine stops.

Current rockets "stage," meaning they drop parts as they go up. Most dropped parts fall back into the ocean. 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 is called a "dogleg." It helps avoid flying over land or areas with many people. Doglegs need extra fuel and can make the flight a bit harder.

Noise

Rocket engines make very loud sounds when they shoot out gas. These sounds can be too loud for people nearby. For example, the Space Shuttle made a noise level of 180 dB, which is extremely loud. To keep the rocket and its crew safe, scientists used a special water system to make the noise less loud.

The loudest noises happen when the rocket is close to the ground. Engineers use special trenches and water to help make the sound quieter. Astronauts inside the rocket are placed far away from the engines to stay 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 gives energy to the gases. This energy builds up pressure. A special part called a nozzle turns this energy into movement. This movement pushes the rocket forward.

When gases are at the top of the engine, they push against it, 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 them speed up 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 happens 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 carefully to keep them safe. Because they hold a lot of strong fuel, problems can sometimes happen. For example, during a test 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 prevent these incidents and to make space travel safer.

Costs and economics

The cost of building a rocket has three main parts: the fuel to make it fly, the weight of the rocket without fuel, and the cost of equipment and launch places.

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

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