Rockets have to lift the fuel and the payload (for example, a spaceship or satellite). So, the more the payload weighs, the more fuel is going to be needed to get it into space.

It would be simple to launch a payload using a rocket filled with solid fuel – just like a giant firework. But you can’t control this kind of rocket. For that you have to use gases, which is more like the way a motor car works.

In a motor car you turn petrol into fine droplets and mix it with oxygen in the air, then burn the mixture. Burning the mixture causes air to expand in the cylinders and that pushes the wheels around.

In space there is no air, so the oxygen has to be carried as liquid oxygen. Petrol would not give enough power, so another fuel is used – often liquid hydrogen. Combining the liquids causes tehm to expand and allowing them to rush out of the back of the rocket causess the rocket to move forward very quickly.

The power is controlled by the rate the gases are pumped to the engine. The rocket is steered by tilting the engines.