Figure 9.18: A lesson from nature in thermal control: polar bears displaying their insulation blankets and thermal radiator surfaces.

devices that produce the most heat are mounted on the interior surfaces of these radiators to keep them cool.

Like many aspects of engineering, this arrangement is a lesson from nature, and is similar to the way a polar bear, for example, manages its thermal control! A polar bear (Fig. 9.18), like a spacecraft, has to survive in a hostile thermal environment. To keep warm in the cold polar regions, it needs good insulation in the form of its fur coat. On the other hand, it does need some effective radiator surfaces, so that it does not overheat when it exerts itself physically or when summer comes. So it has radiators too, such as the pads on its feet, its shiny black nose, and its tongue, to allow its internal heat to be radiated away. Like the spacecraft, it must have enough insulation to keep warm when its environment gets cold, but enough radiator area to cool down when the environment gets too hot.

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