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TURBULENT TIMES

Q: When flying I have often experienced clear-air turbulence. What exactly is it?

A: Clear-air turbulence is often referred to as `rough air' or `air pockets', and is a safety hazard for aircraft, as it cannot be seen, but definitely can be felt. One cause of turbulence is mountainous terrain. For example, a mountain range that is 3,500 metres high can cause turbulence by pushing air up to a height of 6,000 metres. Another cause of clear-air turbulence is the jet stream from other aeroplanes. While flying, planes often try to follow in another plane's jet stream, where the air should be smooth, but when crossing the boundary out of the stream, wind shear will often cause severe turbulence. Unsettled weather can cause turbulence up to approximately 30 kilometres away, but this type of turbulence is known as convective rather than clear-air turbulence.

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SPACE CLEANING

Q: I have often wondered how satellites are kept clean, and whether there are any pollutants that will damage them?

A: Space is full of space dust, which can be caused by either meteorites crashing into the moon and releasing clouds of dust, or the fragmentation of meteorite remains. Even though some of the particles are so small they can not be seen without the aid ora microscope, they can still cause damage because they travel so fast. Individual particles of space dust travel at a speed of at least 14 kilometres per second. During a meteorite shower, particles of space dust may travel as fast as 70 kilometres per second. Such high speeds can mean that dust particles may damage a satellite by colliding with it The majority of satellites are covered in solar panels, which are particularly vulnerable to the effects of space dust. As there is no way of cleaning a satellite once it has been launched, each satellite has to be designed and built with the possibility of damage from space dust in mind.

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