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How does a space rocket work?

Falcon rocket takes off, February 2018Falcon rocket takes off, February 2018In a rocket engine, two different fuels (for example kerosene and liquid oxygen, or liquid hydrogen and oxygen) are mixed together. When ignited inside a combustion chamber, they turn into hot gases that rush out of a nozzle at great speed. This causes the spacecraft, attached to the rocket engine, to be thrust in the opposite direction.

A rocket engineA rocket engine

Escape velocity

To travel into space, a space rocket must reach a speed of 40,000 kilometres per hour (25,000 mph)—ten times the speed of a rifle bullet. This is called the escape velocity. It is the minimum speed needed to escape the Earth’s gravitational pull. Its engines must therefore be both very powerful and able to work without air (there is none in space). Jet engines cannot do this. They are not powerful enough and need oxygen to work. 

Normally, a spacecraft is first launched into what is called Low Earth Orbit (160–2000 kilometres or 100–1250 miles above the Earth). It is then accelerated to the escape velocity from that altitude. The thrust needed is far less than at the Earth's surface. 

Once in space, the spacecraft’s engines can be turned off. It maintains its speed because there is no air to slow it down.

As high as a 30-storey skyscraper, the 111-metre (364-foot) Saturn V rocket was the largest ever built.

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