SPACE TRAVEL I
Although space starts just 100 kilometres above the Earth’s surface, it is very difficult to get there. Aeroplanes cannot reach space because the air gets thinner and thinner with altitude. Their wings begin to lose lift and their jet engines stop working through lack of oxygen. So spacecraft need rocket engines which work in the vacuum of space. To travel in space, a spacecraft must reach a speed of 28,500 kilometres per hour, the minimum speed required to escape the pull of the Earth’s gravity. Once in space, the craft’s engines can be turned off. It maintains its speed because there is no air to slow it down.
In a rocket engine, two different fuels mix and react together inside a combustion chamber, creating hot gases that rush out of a nozzle at great speed. The gases rushing in one direction push the engine and the spacecraft in the opposite direction. The first experimental rocket was launched in 1926 by the American inventor Robert Goddard, but it was not until the 1950s that a rocket powerful enough to reach space was developed. Spacecraft are normally carried into space by rocket-powered launch vehicles, which are huge compared to the spacecraft. For example, the 140-tonne Apollo spacecraft needed a 3000-tonne Saturn V rocket to launch it. Most of the weight was fuel.
The enormous Saturn V, built to launch the Apollo series of spacecraft, consisted of three rocket stages. In a multi-stage rocket, the engines of each stage fire until their fuel runs out. Then the stage is jettisoned (cast off) and the engines of the next stage fire. The rocket gets lighter each time a stage is lost, allowing it to accelerate more easily. This is more efficient than one rocket.
The first stage of a Saturn V had five engines fuelled by kerosene and liquid oxygen stored in huge tanks. It created as much thrust as 50 jumbo jets. The second stage also had five engines, fuelled by liquid hydrogen and oxygen. The third stage had one engine, also fuelled by liquid hydrogen and oxygen.
On top of the 111-metre rocket were the Lunar Module, Service Module and Command Module of the Apollo spacecraft, and an escape rocket, that pulled the Command Module clear of the rocket in case of an emergency during launch.
Robert Goddard’s first rocket reached an altitude of just 12.5 metres. The German V2 long-range rocket (centre) was built as a weapon from 1942. The Soviet Vostok launcher launched the first-ever satellite, Sputnik 1.
Picture Credit : Google
