A prehistoric pigment for a space probe

Artistic concept of the Solar Orbiter space probe during its mission (Image ESA/AOES)
Artistic concept of the Solar Orbiter space probe during its mission (Image ESA/AOES)

Burnt char bone, also known by other names such as bone black, a black pigment already used more than 30,000 years ago in cave paintings will be used to coat the heat shield of the Solar Orbiter (SOLO) space probe. It’s an ESA mission in collaboration with NASA whose launch is scheduled for early 2017. Its purpose is to study the Sun from a relatively close distance of about 42 million km (about 26 million miles).

The Solar Orbiter spacecraft will be equipped with a series of instruments that have the goal of studying the Sun to better understand some of its characteristics. For example, the information collected will be used to understand how the solar wind plasma and the magnetic field in the solar corona are originated, how the solar dynamo works and how solar eruptions produce energetic particles radiation that fill the heliosphere.

The great challenge of the Solar Orbiter mission is to send a spacecraft closer to the Sun than it has ever been done before. In fact, this probe will be closer to the Sun than the planet Mercury. The consequence is that it will be exposed to a light 13 times more intense than on Earth and temperatures that can reach 520 degrees Celsius (about 970° Fahrenheit).

To work in such a tough environment, the Solar Orbiter spacecraft must be built with appropriate technologies. Some of them are the ones developed for the BepiColombo mission, a collaboration between ESA and JAXA, the Japanese space agency, to send a spacecraft to the planet Mercury.

One of the problems in building the Solar Orbiter spacecraft is in the features needed for its heat shield. It must be black to prevent the light being reflected, interfering with the work of the instruments. The color must remain the same for years despite intense exposure to sunlight. It must also be stable, meaning it mustn’t emit dust, gas or electric charges that may contaminate the instruments.

The solution is a modern application of an extremely ancient pigment. The burnt char bone is still used today in various ways and in the case of the Solar Orbiter spacecraft’s heat shield it will be applied using a technology developed by Irish company Enbio for titanium dental implants. The burnt char bone layer will not be painted but it will become part of the titanium layer of the heat shield.

These modern technological applications of substances known to many thousands of years could not stop at this scientific mission. ESA is in fact considering using them to increase the robustness of telecommunications satellites, which are typically in orbit around the Earth but have to remain there for many years. A greater resistance to solar radiation could increase their life and, given their high costs, this would be very positive.

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