A COLOUR-changing skin could help to keep pint-sized spacecraft at comfortable temperatures without the bulk and expense of normal cooling equipment.
If the temperature on board a spacecraft were not controlled, it would swing from freezing to scorching, playing havoc with the on-board electronics. It is usually regulated by pipes that carry refrigerants, or mechanical louvres to reflect the sun鈥檚 radiation. However, these techniques are too bulky for the lightweight satellites now being developed with the aim of slashing launch costs.
A team led by Prasanna Chandrasekhar, working at materials research company Ashwin-Ushas in Lakewood, New Jersey, believe they have a more streamlined solution: a skin less than half a millimetre thick that radiates away heat when a voltage is applied to it. The skin is coated with silicon compounds that reflect a large proportion of the sun鈥檚 visible and ultraviolet radiation. The infrared radiation that penetrates the coating is absorbed by the skin.
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This would simply heat the spacecraft up were it not for the unusual properties of the materials that make up the skin 鈥� an electrolyte sandwiched between two gold-coated polymer sheets. When a small voltage is applied across the sandwich, ions from the electrolyte flow to the sheets, changing the distribution of electrons within the polymer. The visible effect as the voltage increases is a change in colour, from transparent to deep green. More significantly, though, the polymer sheets start emitting infrared radiation. This means a spacecraft could vary the amount of heat it radiates by adjusting the voltage across its skin, thus controlling its temperature.
In tests, a piece of aluminium coated with the skin and subjected to heating by infrared radiation in a vacuum stayed at a steady 60 掳C 鈥� comfortable for electronics. The temperature of a naked piece of aluminium, by comparison, ranged from -50 掳C to 100 掳C.
The work was presented at the American Chemical Society鈥檚 national meeting in Philadelphia this week. NASA plans to perform more extensive tests to verify the skin鈥檚 suitability for space missions.
鈥淣ASA plans more tests to verify the skin鈥檚 suitability for space missions鈥�
Chandrasekhar believes the skin could also be used to insulate buildings in tropical climates, reducing air-conditioning bills and greenhouse gas emissions. But Bill Clyne at the University of Cambridge says that while the skin looks promising, its down-to-earth applications may be limited because radiation is not the main factor in heat transfer in many terrestrial situations, particularly where cooling is concerned.
