The vehicle’s body was constructed from HexCores, which fit together like the pieces of a puzzle. HexCores are 3D-printed from filament made from recycled polyethylene terephthalate (PET), a waste plastic that children in the Dutch city of Zwolle helped collect for the C2A project. The base HexCore shape is a honeycombed hexagon about .8 inches thick, but the C2A team also had to print PET corners, edges and mounting points to create the hull. About 137 different forms were printed, with a total of 2,500 of the printed shapes required for the Solar Voyager construction.
After the hull was built, it was laminated with Teijin’s Tenax® carbon fiber to provide extra rigidity, protect against puncturing and supply strong mounting points for reinforcing areas like the metal A-frames of the suspension.
The underside of Solar Voyager was covered with woven Twaron® para-aramid fiber and an epoxy resin that provided protection against sharp ice. Van der Leeden says that the para-aramid is just one-fifth the weight of steel, but six times its tensile strength. In addition, it offers superior heat resistance and elastic modulus. “Carbon fiber provides tensile strength, but carbon fiber is vulnerable when it comes to side impact,” he says. “Twaron provides greater protection against side impact.”
Teijin designed the wheels using experimentation and early-stage testing validation to find the right approach. It developed two different designs, one very rigid and the other very supple. “We initially choose the rigid one and had to validate it in conditions similar to the Arctic conditions,” van der Leeden says. “This showed quite fast that it was not the right design for this vehicle. We changed it to the more supple design, and in the same conditions this proved to be the right design.” Nets made from Teijin’s Endumax®, a special ultra-high molecular weight polyethylene (UHMWPE), were an integral part of the wheel design, minimizing rolling resistance and maximizing traction. The material also helped soft inflated tires retain their dimensional stability.
The windows of the Solar Explorer were made from self-heating Panlite® polycarbonate (PC) resin, which is 200 times more resistant to impact than glass and half its weight, according to Teijin. The front windows absorbed infrared sunlight to maintain heat inside the vehicle. This wasn’t for passenger comfort – the ter Veldes wore heavy winter gear the entire time – but to prevent ice formation on the windows due to condensation of humid air inside the vehicle.
The ter Veldes carried the HexCore pieces of the Solar Voyager with them to South America and assembled the vehicle there. Although it was summer in Antarctica, their trip in the Solar Voyager wasn’t easy. Because the weather conditions were unusually dangerous, they were never able to make it to the South Pole. But the Solar Voyager, including all the Teijin materials and solutions, performed perfectly, says van der Leeden.
Once the ter Veldes completed their trip, they disassembled the Solar Voyager and returned home to The Netherlands. Although they never reached the South Pole, the couple felt they achieved their goals. They showed that solar-powered travel was possible even in the very difficult environment of Antarctica, and they demonstrated that everything, even waste plastic, can be reused.
Journey to Another World
Although Mercury and Venus are closer to Earth, Mars is the planet that attracts the most attention from scientists and explorers. According to Digital Trends magazine, there have been 56 different missions to Mars to date, although only 25 of them have been successful. There are seven future missions to Mars scheduled through 2024, and spacecraft components made from composite materials will likely be on board for all the flights and on-planet explorations.
One of those upcoming missions is ExoMars, a joint program of the European Space Agency (ESA) and Russia’s space agency, Roscomos. Thales Alenia Space is the prime contractor for the project, which is designed to investigate the Martian environment. The project’s first phase took place in 2016, when the team put a trace gas orbiter in orbit around Mars and tested an entry, descent and landing demonstrator module (EDM). In the second phase, which will begin in 2020, the agencies will land a robotic rover on the red planet.
The robotic explorer, named the Rosalind Franklin to honor a famous British biochemist, will collect and analyze samples gathered from beneath the Martian surface, drilling down as far as 6.5 feet. The agencies hope to find evidence of methane and other trace atmospheric gases that could indicate that life once existed on the planet.
To accomplish its mission, the Rosalind Franklin will have to function in Mar’s extremely cold environment – the average temperature there is minus 80 degrees Fahrenheit. Although the vehicle will run on six wheels that will automatically adjust its height and angle as it moves, the chassis will need to be tough enough to withstand possible contact with Mars’ rocky surface. CFRP materials will provide both the light weight and the durability required for the Rosalind Franklin’s chassis.
Airbus Defense and Space is developing the Rosalind Franklin, with RUAG Space supplying many of the parts. RUAG tapped the engineering company Scheurer Swiss to assist in the development of the rover’s CFRP chassis.
Scheurer Swiss had previously worked with RUAG Space on the Sentinel and other ESA satellites. “RUAG Space had already had several good experiences with us and knew about our engineering competence,” says Dominik Scheurer, CEO of Scheurer Swiss. “In the course of the project, our services expanded from engineering to consulting on a laser system for the laminating process, 3D ply flattening and production support on site.”
Airbus and RUAG Space decided to use CFRP for the chassis at a very early stage. “No other materials could provide the requested properties regarding strength and temperature resistance,” Scheurer adds.
The chassis was made with a high-performance prepreg and a cyanate ester resin. To improve the speed of manufacture and the quality of the completed product, Scheurer recommended that RUAG use software to transform its 3D model into a 2D pattern, and that laser projection be used for the lamination process. “Our goal was to introduce well-known, production-related engineering from motorsport to a space application,” he explains.
Using laser projection, manufacturers can verify the position of the tool and then project the outline of each ply for lay-up. “In the normal, old-fashioned way (lay-up), you have to measure and position every single ply by hand into the right position,” says Scheurer. “In the reinforced areas of the chassis, that could mean positioning up to 50 plies. Without laser projection, the lamination process would be very time consuming.” The use of six laser projectors around the tooling also eliminated issues related to the short 20-day lifespan of the high-performance prepreg.
Scheurer Swiss started work on the project in the summer of 2016 and completed its role by the end of 2018. During this time, RUAG built three different models of the rover. The final version of the Rosalind Franklin was built in a special clean factory at Airbus Defense and Space in England. The clean room construction helped ensure that organic materials are not accidentally carried to Mars, which would contaminate the experiment. The rover then went to Airbus Toulouse in France, where it was tested in a simulated Martian environment.
The Proton rocket that will carry the Rosalind Franklin and its Russian-built descent module is scheduled to launch next summer, and the Rosalind Franklin should be on Mars sometime in early spring 2021. Scheurer is confident that the composite materials will perform as expected throughout the mission and beyond. “Composite materials are engineered to survive the harsh environment,” he says. “Once composite materials have been cured, they have no expiration date.”
