If you think of a 'rocket', you might think of a vehicle which flies people to space.
But did you know that a rocket is also a type of engine?
We use rocket engines to send humans, satellites and robots into space.
This lets us explore space and send information around the globe.
- How does a rocket engine work?
You may have heard a character on TV or in a film say, "Engage thrusters!" Like with many engines, it is something called thrust which drives rockets along.
You may have experienced thrust at home. Have you ever turned on a garden hose and felt it push back into your hand? This is an example of thrust—the backward thrust results from the water being pushed out of the hose.
Rockets create thrust by burning fuel at high temperatures. This makes a huge explosion. The gas from the blast escapes from the base of the rocket down towards the ground. This results in the thrust that propels the rocket in the opposite direction, up to space!
It even works in the vacuum of space where there is no air! Isaac Newton's '3rd Law of Motion'describes this process, "For a given force in one direction, there is an equal and opposite force in the opposing direction."
- What kind of fuel does a rocket use?
There are two main types of rocket engines. Some use liquid fuel, and others use solid fuel.
Most modern liquid fuel engines use liquid hydrogen as the fuel and liquid oxygen as the oxidizer. When lit, this mixture burns at very high temperatures, up to about 3000 °C.
Rocket scientists on Earth can use remote controls to change the amount of thrust this type of engine makes. They can even stop and restart the engine while it is in flight.
The big challenge with these engines is that hydrogen and oxygen stay liquid at very low temperatures. They must be kept at minus 150 °C and below! It is a huge challenge to keep fuel this cold on a spacecraft. It involves an area of science called 'cryogenics'.
Solid fuel engines carry a 'solid' block or brick of fuel. The fuel mixes powdered aluminium and an oxidizer, usually ammonium perchlorate. This type of rocket does not need to keep the fuel in super-cold tanks.
The challenge with this fuel is that once it is lit, it must keep on burning until it is all used up. Small rockets fixed to the main rocket's outside often have solid fuel engines. These are also known as booster rockets. Fireworks and model rockets use solid fuel.
- What does a rocket engine contain?
Liquid fuel engines contain pumps which mix the fuel and oxidizer. The fuel burns in the combustion chamber, creating an explosion. The gas from the explosion is forced through a narrow part of the rocket called the throat. This increases the pressure and produces greater thrust.
A nozzle directs the exhaust out of the base of the rocket. Solid fuel rockets contain a solid block of fuel in a combustion chamber. An igniter lights the solid fuel mixed with an oxidizer. Like in liquid fuel engines, the burned propellant is forced through a throat in the rocket. A nozzle directs the exhaust out of the base of the rocket.
- When were rockets invented?
China was the first country to use rockets in the 1200s. These solid-fuel rockets were used as fireworks and weapons in war. Over the next 700 years, people around the world made powerful solid-fuel rockets. They were still mostly used as fireworks or weapons.
A Russian scientist in the early 1900s came up with the idea of liquid fuel engines. An American scientist was the first to launch a liquid-fuel rocket in 1926. German scientists built powerful liquid fuel rockets to use as weapons during World War II. In 1957, Russia became the first nation to launch a space probe using a rocket.
One of the most famous rockets invented was the Saturn V (as in five in Roman numerals). This rocket was used to get people to the Moon in the 1960s and 1970s and to launch one of the first space stations, SkyLab.
- A short history of rockets
Saturn V remains one of the tallest, heaviest, and most powerful rockets ever. And all of its official launches were successful. The rocket consisted of three stages, each containing a rocket engine and fuel. The first stage used kerosene rocket fuel, and the second and third used liquid hydrogen. The three stages were stacked up, with the first stage at the bottom of the rocket and the third at the top. The Saturn V rocket stood 18 m taller than the Statue of Liberty and 15 m taller than the Big Ben clock tower!
Soyuz rockets were introduced in 1966 in Kazakhstan near Russia. By the 1980s, 60 rockets per year were being made. These rockets have been used over 1700 times—far more than any other rocket in the world. They transport astronauts and supplies to the International Space Station (ISS) in manned and unmanned missions. Soyuz rockets are also used by commercial companies, as they are low-cost but very reliable. The rockets use liquid oxygen fuel.
After launch, the rocket separates from the capsule, which holds the astronauts and the supplies. The rocket returns to Earth, and the capsule continues upwards, reaching space in only 9 minutes. The Soyuz capsule takes 6 hours to get to the ISS. These rockets have lasted the test of time and are still regularly used.
All traditional rockets were used once and then burned up in the atmosphere when returning to Earth, crash-landed back on Earth, or drifted off into space. Some modern companies building rockets, like SpaceX, are producing rockets that can be used again and again, making each one cheaper and more environmentally friendly (though rocket launches produce a lot of emissions!). An example is the Falcon 9 rocket, which has been used since 2010.
Falcon 9 rockets are made of two sections called stages. SpaceX Merlin engines power both stages. The engines use liquid oxygen and rocket-grade kerosene as fuel. The first stage re-enters the Earth's atmosphere after launch. This means parts of the rocket can be used again. These rockets can only be used to put objects into orbit around the Earth.
It is much more difficult to make rockets capable of safely lifting humans into space and launching space probes into deep space. Although many private companies and space agencies are designing and testing these heavy-lift rockets, a direct replacement for the Saturn V rocket still needs to be developed.