There would be no space exploration without rockets, but they are not a modern invention. The Chinese developed the first rockets around ad 1200. Unlike ordinary engines, a rocket carries its own supply of oxygen to burn its fuel. That is why it can work in airless space. The fuel and oxygen-provider, or oxidizer, are called propellants, because when they burn they produce a stream of gases that propels the rocket forwards.
Russian space exploration has used the Soyuz launch vehicle since the 1960s. Measuring nearly 50 m (165 ft) tall, it is a combination of three sets of rockets linked together. Four booster rockets surround a centre rocket, or core stage. A second stage sits on top, with the Soyuz spacecraft on top of that. Each rocket burns kerosene and liquid oxygen.
In a rocket, fuel is burned in oxygen in a combustion chamber to produce a mass of hot gases. The gases expand and stream backwards out of the rocket. The force as they stream out backwards sets up a reaction force in the opposite direction, called thrust, which propels the rocket forwards.
Practical space rockets, or launch vehicles, are made up of several rocket units joined together. This arrangement is called a step rocket. The principle behind the step rocket is that each rocket unit, or stage, fires for a time and then falls away when the fuel has been used. This makes the rocket lighter and enables it to accelerate faster.
Robert Goddard fired the first liquid-propellant rocket on 26 March, 1926. It used petrol and liquid oxygen as propellants. In 1919, he was ridiculed when he said that rockets could be used to fly to the Moon. This earned him the nickname “Moony Goddard”, and for the rest of his life he tried to avoid publicity.