When the European Space Agency (ESA) designed a spacecraft to fly closer to the sun than any other probe in history, it faced a major problem: how to shield the probe from extreme heat and radiation.
A joint mission with NASA, the Solar Orbiter launched in February 2020 and recently emerged from its first pass behind the sun. It has to be able to withstand temperatures hot enough to melt lead, as well as 13 times the radiation that reaches the Earth’s surface.
At first, the agency looked for conventional solutions, based on metals and carbon fiber, but they were not good enough, Cesar Garcia Marirrodriga, ESA’s project manager for Solar Orbiter, told CNN Business. Instead, the agency found the answer in a material that dates back to the Stone Age.
An ancient pigment
After ESA put out an invitation for solutions, it was approached by Irish biotechnology company ENBIO. It had developed a technique to apply synthetic bone coatings to orthopedic and dental implants, to make them more easily accepted by a patient’s body. Because the technique reduced weight and prevented issues like flaking, ENBIO thought it could be useful for the titanium surfaces of Solar Orbiter.
But the synthetic bone was light-colored and testing showed that it would darken after prolonged exposure to sunlight, changing the amount of heat it absorbed and reflected. A black coating meant its properties would be stable for the whole mission, absorbing the sun’s energy as heat and then dumping that into space.
Solar Orbiter's mission to observe the sun
“I tried to color the bone powder to make it black, but it didn’t work too well,” recalled John O’Donoghue, the founder of ENBIO.
Instead, he started looking for a naturally black bone powder. “I remembered reading as a kid that in cave art, people used charcoal and, in some cases, [burnt] animal bones, because the end of it would be like a crayon and they could draw on walls,” he said.
After O’Donoghue sourced some burnt animal bone powder, ESA found it was ideal for the solar mission. In addition to being black, there’s nothing combustible left in the material — so when it’s heated up it, doesn’t release any gases that could damage the spacecraft, explained Garcia Marirrodriga.
The resulting coating, called SolarBlack, covers about a fifth of Solar Orbiter’s surface area, and keeps its most delicate parts operating at room temperature while absorbing heat up to 1,000 degrees Fahrenheit. ENBIO, in collaboration with Airbus (EADSF), also developed SolarWhite, a white coating that covers other parts of the satellite where sunlight needs to be reflected rather than absorbed.
Aiming for space
O’Donoghue’s interest in coating technology began while studying biomedical engineering at Trinity College in Dublin. He founded ENBIO in 2006 and in 2015, the company opened a €1.5 million ($1.8 million) industrial coating facility in Clonmel, about 100 miles southwest of Dublin. Solar Orbiter has earned the company several million euros, according to O’Donoghue, and ESA has deployed SolarBlack on other missions.
O’Donoghue said the coatings and the coating process can find applications in the automotive, metal, heating and energy industries, among others, but the current focus lies beyond this planet. “We aim for the space sector because we felt if we go to the top of the pyramid and [do well there], the rest of the industry will be more accepting of it,” he said.
Although its main mission won’t start until November, last July Solar Orbiter sent back the closest images of the sun ever taken.
Over the next few years, the €1.5 billion ($1.8 billion) mission will use the gravity of Earth and Venus to slingshot itself ever nearer to the sun, eventually achieving a closest pass to the star within the orbit of Mercury. “The goal is to really understand the physics of how the sun creates and controls the heliosphere (the area around the sun), and why the solar activity changes over time,” said Garcia Marirrodriga.