Probe to use Prehistoric Pigment Shield for Solar Plunge

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When Captain Jean Luc Picard commands “Shields up!” it’s usually in response to a violent encounter with the Borg, resulting in a translucent field of protective energy surrounding the hull of the Starship Enterprise. Although the precise sci-fi nature of “shield technology” is never fully explained, a real world analogy for shield technology could include the Earth’s magnetosphere, which acts as a magnetic deflector shield of sorts — as energetic solar wind particles hit our global magnetic field, they are captured and redirected to rain down at high latitudes, creating aurorae.

But say if you had a spacecraft you want to fly close to a star? Lacking 24th century technology (or a planet-sized geomagnetic field generator), scientists may opt to bulk out the spacecraft with thick, heavy material, protecting the components inside against the searing heat and intense radiation. But this option would cause launch costs to skyrocket, potentially killing the project before it even reaches the launch pad.

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European scientists designing the upcoming Solar Orbiter — a mission that will swoop deep inside the sun’s atmosphere (the corona) to carry out an unprecedented solar observing campaign — didn’t turn to science fiction for help, however. They’re using a technology that was available during prehistoric times to protect the spacecraft from the sun.

Already sporting hi-tech titanium armor, Solar Orbiter scientists are using a novel technique to apply burnt bone charcoal to the armor’s surface. This charcoal pigment can be found in prehistoric cave drawings created by our ancient ancestors, notably in the Chauvet Cave paintings in southern France dating back to 30,000 years ago. But what was once a rudimentary art tool has now become a sophisticated solar mission’s shield technology.

Scheduled for launch in 2017, the Solar Orbiter will dive 42 million kilometers from the surface of the sun (closer than Mercury’s orbit) enduring 13 times the intensity of sunlight our planet receives. Due to its proximity, the mission will be cooked to a hotter-then-charbroiled 520 degrees Celsius (970 degrees Fahrenheit).

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“The main body of the spacecraft takes cover behind a multi-layered 3.1 meter by 2.4 meter heatshield,” said Pierre Olivier, Solar Orbiter’s safety engineer. “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.”

But there’s a problem. During the planning phase in 2010, planners realized that to maintain constant shield color over years of operation, a novel technique would need to be found. Basically, after years of extreme exposure to the sun, the shield’s color cannot change. If it does, its heat-absorption properties will also 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’ — keep the same color despite years of exposure to extreme ultraviolet radiation,” said 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. 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,” he added.

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Conventional space materials were ruled out, so mission designers looked at the medical sciences for help.

The Ireland-based company Enbio was enlisted. Using its CoBlast technique that was developed to coat titanium medical implants, the company tested the application of black calcium phosphate to the titanium shield of Solar Orbiter. Rather than being “painted” onto the surface, the CoBlast technique bonds the material into the titanium.

Black calcium phosphate, or burnt bone charcoal, has just the right thermo-optical properties for Solar Orbiter’s shield and this medical application ensures that it doesn’t get eroded in the extreme coronal environment. The material has been dubbed “Solar Black.”