European scientists came across a conundrum while designing the upcoming Solar Orbiter: How to shield it from the heat of the sun, without loading it down with heavy armor that would make the expense of liftoff so drastically high that the mission would be an impossibility from the start? The solution, they realized, was in prehistoric cave paintings.
For the Solar Orbiter’s unprecedented solar observing mission — which will send it swooping deep inside the corona of the sun — its first layer of defense will be futuristic and modern: a hi-tech titanium armor. It’s prehistoric element: burnt bone charcoal.
The charcoal will be applied to the outer surface of the titanium armor. The same charcoal pigment can be found in cave drawings, notably the Chauvet Cave paintings in southern France that date back 30,000 years ago. Little did our ancient ancestors know that their rudimentary art tools would be used in an elaborate sophisticated solar mission.
Solar Orbiter isn’t scheduled for launch until 2017. Scientists plan for the Solar Orbiter to dive close to Mercury’s orbit, about 42 million kilometers from the surface of the sun, where it will endure 13 times the intensity of sun life Earth receives. At the peak of proximity the temperature is expected to be 970 degrees Fahrenheit (520 degrees Celsius).
While scientists designing Solar Orbiter equipped it with the necessary protection and the main body will be sheltered by a multi-layered heat shield, the planning process revealed a twist. In order to maintain long-term exploration — years of orbiting in close proximity to the sun — the spacecraft’s heat shield cannot change color. If it does, its heat-absorbing properties would change.
“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,” said materials technology specialist Andrew Norman.
Ruling out conventional space materials, mission designers realized a novel approach would need to be found. They found themselves looking to the medical sciences. The company Enbio was enlisted to help. The company uses a technique known as CoBlast, that was developed to coat titanium medical implants. Using this technique to apply burnt bone charcoal (black calcium phosphate) to Solar Orbiter’s shield proved genius. The charcoal have just the right thermo-optical properties for the shield, and the CoBlast process enables the charcoal to bond into the titanium instead of merely being “painted” to the surface, ensuring that the shield will not erode in extreme coronal environment. The material has been termed“Solar Black.”