While the use of composites in creating Juno was not new, some of the problems they solved using composites were unique. “For example, it’s the first solar-powered mission this far from the sun, so the solar panels needed to be uniquely designed to fit in the spacecraft but large enough to absorb the sun’s rays. Many important parts also needed to be protected from the strong magnetic field around Jupiter,” says Rawal. “Composites usage is an industry practice now but we wanted to insert nanotubes as a new technology replacement for aluminum foil for electromagnetic (EMI) shielding.”
“We were approached to provide protection against ESD for several critical components of Juno, such as the thrusters and the main engine cover,” says Peter Antoinetti, president of Nanocomp Technologies, Merrimack, N.H. “When Juno approaches Jupiter it has to slow down to be pulled in by the planet’s gravitational pull. Part of that process means traveling through Jupiter’s extremely strong radiation belts.” At that point the main engine will have been sitting untouched for five years; and it has to open and fire successfully. Coupled with that challenge was the need to protect Juno’s electronics, controls and motors from the ESD. To protect them, the group used a dry sheet nanotube, which was made into a prepreg and co-cured around the honeycomb core.
Rawal’s team at Lockheed Martin was involved in the development of an alternative ESD solution to the traditional aluminum foil that is typically bonded to the surface of composites. According to Antoinetti, the benefit of CNTs are their ability to be incorporated directly into the carbon composite. The group evaluated other CNT-based solutions and chose CNT-based sheets even though it is a new material because it gave the protection the spacecraft needed without adding any parasitic weight. “Lockheed Martin was able to qualify Nanocomp’s CNT sheet material within a year because it’s in a format that engineers prefer,” says Rawal. “During manufacturing the CNT sheet layers were added during composite fabrication.” He adds that the CNTs were able to drop directly into the system, saving 10 percent of manufacturing time.
“The successful launch and the mission completion of Juno in 2017 are momentous occasions for composites and more, especially CNTs,” says Antoinetti. “It opens a way for broader adoption of these products. I’m confident they will continue to gain acceptance by conservative engineers because they solve problems, they’re easy to use and hopefully that means larger scale adoption into more primary structures. In a sense, the goal is to be a key component in the tool box of engineers to make better structures.”
