Prehistoric cave painting pigment to save probe from Sun's heat
The European Space Agency's (ESA) upcoming Solar Orbiter will undertake a daunting mission - it will gaze into the fiery heart of the Sun. However, it's going to need a lot more than a titanium heatshield to survive and scientists seem to think a prehistoric cave painting pigment may hold the key to success.
ESA scientists have announced that they are planning to coat the Solar Orbiter's heatshield with a material processed from burnt bone charcoal to protect it from the Sun's fierce rays. The upcoming orbiter will be operating at a distance of 26.09 million miles away from the Sun. While this may seem like a large distance, it is but a stone's throw away in astronomical terms. At this distance, the orbiter will be exposed to sunlight that is 13 times more intense compared to what we get on Earth. Moreover, the orbiter will also need to withstand temperatures as high as 520°C (968°F).
"The main body of the spacecraft takes cover behind a multi-layered 3.1 m by 2.4 m heatshield," says ESA safety engineer Pierre Olivier. "And Solar Orbiter's instruments will operate at the far end of 'feed-through' lines that run through the shield, some under protective covers of beryllium or glass."
ESA's Solar Orbiter will be launched in the year 2017. Since the orbiter will be carrying sensitive equipment that will be responsible for taking high-resolution images of the Sun, the orbiter will require adequate shielding.
"We soon identified a problem with the heatshield requirements," said ESA materials technology specialist Andrew Norman. "To go on absorbing sunlight, then convert it into infrared to radiate back out to space, its surface material needs to maintain constant 'thermo-optical properties' - keep the same colour despite years of exposure to extreme ultraviolet radiation."
Scientists have been investigating compounds and substances with potential heat shielding properties and they have discovered that burnt bone charcoal can enhance a titanium heatshield's protective capabilities. Scientists first considered using carbon fiber fabric. However, the ESA team kept on looking for materials that can do a better job.
After looking for other potential materials in other industries unrelated to space technology, the ESA scientists happened upon an Irish medical company called Enbio. Enbio specializes in manufacturing medical implants and the company developed a titanium coating technique called CoBlast, which is used to coat medical implants made of titanium.
"The process works for reactive metals like titanium, aluminium and stainless steel, which possess a surface oxide layer," says Enbio managing director John O'Donoghue. "We spray the metal surface with abrasive material to grit-blast this layer off, but - as the CoBlast name suggests - we also include a second 'dopant' material possessing whatever characteristics are needed. This simultaneously takes the place of the oxide layer being stripped out."
The Enbio CoBlast process uses a material very similar to the pigments used by cavemen in the famous Chauvet Cave paintings in France. Enbio will coat the exterior of the Solar Orbiter's titanium heatshield with a material called "Solar Black," which is a black calcium phosphate based material derived from burnt bone charcoal.
"The big advantage is that the new layer ends up bonded, rather than only painted or stuck on. It effectively becomes part of the metal - when you handle metal you never worry about its surface coming off in your hands," Donoghue said.