In late October the phone booth-sized satellite was placed in the 4.5 m-diameter Phenix chamber in ESA’s ESTEC Test Centre in Noordwijk, the Netherlands – the largest spacecraft testing facility in Europe.

Once inside, the air was pumped out to create a space-quality vacuum at the same time as the temperature extremes in Galileo's planned orbit were also reproduced. The six copper walls of the 'thermal tent' were independently cooled by liquid nitrogen down to the –180°C chill of sunless space.

With no air to transfer heat, the opposing sides of satellites in space can become very hot and very cold simultaneously, depending on whether they are in sunlight or shadow. But satellite systems – in Galileo's case that includes two different types of atomic clocks accurate to a few billionths of a second – must still work perfectly.

Thermal control is a critical design concern, seeking to maintain a set operating temperature within the body of the satellite. This is why some of Galileo's surfaces are covered with reflective mirrors while others are shrouded in black multilayer insulation.  (picture © ESA)

Heaters warm up some areas of the satellite that become too cold, while heat pipes threaded through the structure carry away unwanted heat to the radiators, cooling other areas. [...]

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