Dr. William Kaukler, a longtime NASA contractor and an associate research professor at the University of Alabama Huntsville’s (UAH) Rotorcraft Systems Engineering and Simulation Center, has been awarded a patent for an environmentally-friendly, ionic process to make carbon fiber used in ablative rocket nozzles and heat shields.
Dr. Kaukler developed the new ionic process at UAH’s Reliability and Failure Analysis Laboratory with funding from the U.S. Army’s Aviation and Missile Research, Development and Engineering Center (AMRDEC). As UAH staff writer Jim Steele explains, “to form a solid fuel rocket nozzle, layers of carbon fiber fabric made from carbonized rayon are coated with pitch and wound around a mandrel, and then heat-treated to convert the pitch to solid carbon.”
The resulting nozzle will be a carbon fiber composite. The rocket nozzles of Army missiles are made from phenolic resin and this same carbon fiber. However, unlike traditional carbon fiber, made with a precursor material known as polyacrylonitrile (PAN), Dr. Kaukler used cellulose fiber, which is important because it has a much lower rate of thermal conductivity.
“This carbon fiber is not the same fiber that you’d go out and make aircraft or car parts from,” says Dr. Kaukler. “This is the only way to make the carbon fiber that is suitable for rocket nozzles, is to start with cellulosic fiber.”
Steele says that heat created from the rocket’s burning fuel slowly burns away the interior of the nozzle in flight. Therefore, a low-conductivity fiber composite keeps a propellant’s heat in for more propulsion efficiency, which prevents the nozzle from burning away too quickly in flight.
He adds that the process could be of interest to NASA, whose old cellulose rayon fiber processes created hazardous byproducts. The greener process could be used for NASA’s solid rocket motors in its next-generation Space Launch System. According to Dr. Kaukler, it could be useful for heat shields used in re-entry to Earth’s atmosphere or on planetary probes designed for landing.