Solar Orbiter
February 13, 2014

Prehistoric Cave Painting Pigment To Be Used By ESA For Solar Orbiter Heatshield

redOrbit Staff & Wire Reports - Your Universe Online

Burnt-bone charcoal, a pigment once used as part of prehistoric cave paintings in southern France, will be applied to the ESA’s Solar Orbiter to help protect the vehicle from the Sun’s rays, the agency announced Wednesday.

The spacecraft, which is currently scheduled to launch in 2017, will have a type of black calcium phosphate produced from the substance applied to the outermost titanium sheet of its multilayered heatshield, ESA official said in a recent statement.

Known as Solar Black, the phosphate is produced by an Irish firm known as Enbio. The company traditionally originally developed its CoBlast technique to coat titanium medical implants, but in three years it will be used to protect the Solar Orbiter from temperatures as high as 520 degrees Celsius.

“The main body of the spacecraft takes cover behind a multi-layered 3.1m by 2.4m heatshield,” safety engineer Pierre Olivier said in a 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.”

The Solar Orbiter, which will use multiple instruments to complete high-resolution imaging of our parent star from distances as close as 42 million kilometers away, will also face sunlight levels up to 13 times higher than those on Earth. The burnt-bone charcoal-based substance will be tasked with protecting it from that glare.

During the initial planning stages four years ago, ESA mission specialists started working to ensure that the mission could be successfully completed using current manufacturing materials and techniques. They soon discovered that there was an issue with the heatshield requirements for the project.

“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 color despite years of exposure to extreme ultraviolet radiation,” explained materials technology specialist Andrew Norman.

“At the same time, the shield cannot shed material or outgas vapor, because of the risk of contaminating Solar Orbiter’s highly sensitive instruments,” he added. “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.”

Initially they were planning on using carbon-fiber fabric, but ultimately that was eliminated as a possibility. That’s when they found the CoBlast process, which according to Enbio’s managing director John O’Donoghue, works for reactive metals such as titanium and aluminum that possess a surface 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,” O’Donoghue said. “This simultaneously takes the place of the oxide layer being stripped out. 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.”

The burnt 'char bone' which will be used to protect the Solar Orbiter is also commonly used in fertilizer, to purify white sugar and to filter out heavy metals from water. It has also proven that it can stand the test of time, as it was used in the immensely well-preserved Chauvet Cave paintings in southern France.

“The CoBlasted Solar Black titanium has passed a gamut of testing in ESA’s Materials and Electrical Components Laboratories in the ESTEC technical center in Noordwijk, the Netherlands – everything from accelerated lifetime exposure to sunlight and ultraviolet radiation to the deceptively simple-sounding ‘tape pull’ – applying then pulling off adhesive tape to see if anything comes with it,” the space agency said.

“The treated titanium is now baselined for the heatshield, being developed by Thales Alenia Space in Italy,” the ESA added. “A prototype ‘structural and thermal model’ is due to be tested inside ESTEC’s Large Space Simulator, a giant vacuum chamber featuring a simulated Sun.”