Space

ESA's Solar Probe to be Protected Using Prehistoric Cave Pigment

Benita Matilda
First Posted: Feb 13, 2014 10:01 AM EST

European Space Agency's engineers will use burnt bone charcoal to protect its solar probe from the harsh glare of the Sun.

Burnt bone charcoal, also used in prehistoric cave paintings, will be used by scientists in the titanium heatshield of ESA's Solar Orbiter spacecraft. This will help in protecting the Orbiter from the strong glare of the Sun.

The Solar Orbiter, due to launch in 2017, will carry a range of instruments in order to conduct high-resolution imaging of the Sun, our parent star, from a close distance of 42 million km i.e. slightly more than a quarter of the distance to Earth. The temperatures will be as high as 520 degree C.

"The main body of the spacecraft takes cover behind a multi-layered 3.1 m by 2.4 m heatshield," explained Pierre Olivier, Solar Orbiter's safety engineer, in a press statement. "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."

During the initial planning phase, material specialists said a solar probe mission was possible if  an appropriate heatshield could be found.

"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. At the same time, the shield cannot shed material or outgas vapour, because of the risk of contaminating Solar Orbiter's highly sensitive instruments. And it has to avoid any build-up of static charge in the solar wind because that might threaten a disruptive or even destructive discharge," said Andrew Norman, a materials technology specialist. 

The engineers ruled out carbon fiber fabric, their first choice, as it is a light polymer. Then they hunted for other options.

They then turned to the Irish company, Enbino. This company makes titanium medical implants. They use the CoBlast technique that is best suited for reactive metals like titanium, aluminium and stainless steel, basically metals that have a surface of oxide layer.

"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," commented John O'Donoghue, Managing Director of Enbio.

With this, the new layer gets bonded and effectively becomes a part of the metal. The company will apply 'Solar Black', to the outer titanium sheet of the probe's multi layered heatshield. Solar Black is a type of black calcium phosphate that is developed from burnt bone charcoal.

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