How Do They Do It?

Monday 4 October, 7:30pm on Five

This factual series lifts the lid on the incredible engineering behind everyday life. Presenter Robert Llewellyn is on a quest to understand the extraordinary engines, machines and structures that form the backbone of 21st-century living. This week, Robert focuses on the science and technology behind satellite navigation, and the mass production of aluminium. This week’s show sees Robert turn his attention to a piece of technology that millions of motorists take for granted – the satnav. Since it was completed in 1994, the Global Positioning System (GPS) has become indispensable for aeroplanes crossing continents, ships crossing oceans and for countless weekend car journeys. In-car satnav devices can pinpoint a vehicle’s position to within three metres and provide accurate directions for journeys over thousands of kilometres. But how does the system work? GPS has three stages, known as the space, control and user segments. In space, nearly 30 NAVSTAR satellites orbit the Earth. These satellites relay signals bearing details of both their flight path and the time, accurate to within a few nanoseconds. On the ground, the 50th Space Wing control station at Schriever Air Force Base in Colorado monitors the satellites and ensures their signals are accurate. And in each little satnav device, a GPS receiver picks up the signals from at least four satellites, then uses the time taken for the signals to arrive to pinpoint its position. The device then uses that information to place the driver on a detailed map. Aluminium has become so indispensable to modern industry that some 100,000 tonnes of the metal are consumed every single day. From cans to cars, foil to fighter jets, life would not be the same without aluminium. But how is enough metal produced to cope with such a high demand? At Alcoa’s Huntly mine in Western Australia, some 18 million tonnes of the aluminium ore, bauxite, are extracted each year. In order to be turned into aluminium, the ore is first carried along a 15km conveyor belt to be crushed and washed, then dissolved in hot caustic soda. As the solution cools, seed crystals are added and the valuable metal crystallises as aluminium oxide.

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