Have you been following the story of the latest shuttle mission? Discovery was launched on 4 July and is due to return on 17 July. Everyone is anxiously awaiting its safe return after two tragic accidents involving the shuttle Challenger in 1986 and Columbia in 2003. In the current mission an astronaut was taken up to the Space Station. The other aim of the mission was to check out safety procedures following the previous accidents.
So how does the shuttle work? Well it was developed to be a method of transporting people and goods to and from the space station. It is designed like an aeroplane so that it can land easily and be reused. The aeroplane bit is called the space orbiter; this carries the astronauts. It is mounted on the back of a large main fuel tank which has two booster rockets either side. The whole thing is launched from a launchpad. The booster rockets and the orbiter’s main engines provide thrust to push the whole thing upwards to escape the pull of the Earth’s gravity. So much fuel is needed that two minutes after launch the booster rockets are all used up. The empty rockets parachute back down to Earth where they are collected and reused. In the Challenger accident there was a problem with one of the booster rockets and it ignited. This caused the shuttle to explode and all on board were tragically killed.
The orbiter and the main fuel tank continue to accelerate upwards to a speed of around 18,000 mph! (A speed nine times as fast as the average rifle bullet!). It needs to get beyond the Earth’s atmosphere so that air friction does not slow it down or heat it up. Then it is held in orbit around the Earth. So what does ‘in orbit’ mean? Earth orbit happens when the speed of a spacecraft travelling around the Earth exactly balances the gravitational attraction exerted by the Earth on the spacecraft. I.e. if we can travel quickly enough then maybe we can outrun gravity. When it is in orbit it stops its engines and only uses smaller engines from time to time to nudge it back on track. The main fuel tank is now empty and is ejected. It burns up as it falls through the Earth’s atmosphere. In orbit astronauts (who are scientists) perform investigations and observations. These may help us in the future e.g. possible cures for disease, observing climate change damage etc. When it is time to return the orbiter engines point it towards the atmosphere. As it enters the atmosphere it is pulled towards Earth by gravity. The air friction heats the shuttle up so it needs to have very good heat shields to protect it. The orbiter finally lands just like an aeroplane. In the Columbia disaster the heat shields were damaged when the shuttle was launched. The mission continued successfully. However when it tried to return the heat build up caused the shuttle to explode. Once again, sadly, all on board were killed.
If you want to know more about the shuttle then check out the NASA site.
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