The temperature of the satellite is controlled using a color changing (electrochromic) film coating on the radiator panel. As a voltage is applied, the film changes color – light to dark – to increase the emissivity of the radiator panel. With this control, the spacecraft can change the amount of heat absorbed or expelled to maintain its operating temperature. The main chemical component used in this film is titanium dioxide (TiO2).
Titanium dioxide has only recently been studied for its electrochromic properties and applications. One of the most common uses of this chemical right now is for its white color. You know that white powdered donut you ate for breakfast? That was significantly covered in titanium dioxide! And the lifeguard with the white stripe of sunscreen across his nose? That’s titanium dioxide too! Titanium dioxide is widely used by the food industry for coloring, but its safety has recently been questioned due to the nano-particles’ ability to travel through the human body barriers with unknown consequences.
Unfortunately you can’t just apply a voltage to your donut to get it to change colors too. The reaction that takes place to change the emissivity of the radiator is a reduction-oxidation (redox) reaction involving the exchange of electrons. There are other chemical components added to the film to react with the titanium dioxide that facilitate the required electron transfer. This chemical film is applied to a black anodized aluminum radiator panel and covered with a clear conductive glass which act as the two electrodes of the redox reaction.
This film is currently being developed by the Spacecraft Thermal Management Team and will be initially tested by reversing its mode of function – when taken into the sunlight, it will absorb energy and convert it to a voltage, like a solar cell. This variable emissivity design was chosen for our spacecraft for its low cost relative to current aerospace radiator designs and lack of moving parts, increasing reliability and longevity.
By Amy Dunford, Spacecraft Thermal Management