A patent has been awarded for a new, environmentally friendly process for producing the carbon fibers required for ablative rocket nozzles and heat shields. The new process could provide a way to replenish NASA’s dwindling stockpile of cellulose rayon fiber, which has been out of production since the 1990s because of its hazardous by-products.
Rayon Rocket Nozzles
Rocket nozzles and heat shields must withstand extreme conditions upon re-entry into the atmosphere, and so require specialized materials to produce. “This carbon fiber is not the same fiber that you’d go out and make aircraft or car parts from,” explained William Kaukler, who developed the new process.
The process aims to replicate the properties of NASA’s current stock of fiber, which was produced by the North American Rayon Corporation (NARC), before the company ceased production due to regulations imposed by the Environmental Protection Agency (EPA). The specialized NARC rayon fibers were utilized by NASA in the Space Shuttle program.
“Other people know about using ionic processes to make fibers, but they are not making carbon fibers with them,” said Kaukler. “The trick was to make the properties of this fiber match the properties of the North American Rayon Corp. (NARC) fiber.”
To form a rocket nozzle, you start with layers of carbon fiber fabric made from carbonized rayon. These layers are coated with pitch and wound around a mandrel. After a heat treatment, the pitch is converted to solid carbon, and the result is a nozzle made of a carbon fiber reinforced-carbon composite.
The use of rayon (cellulose fiber) distinguishes the rocket-ready carbon fiber from the more common polyacrylonitrile-based carbon fiber used in structural applications.
“[The] only way to make the carbon fiber that is suitable for rocket nozzles is to start with cellulosic fiber… because it has the lowest rate of thermal conductivity of any fiber,” said Kaukler. The low thermal conductivity is necessary to prevent the rocket nozzle from burning away in flight.
In addition to helping NASA, scaling up the new carbon fiber process could benefit any number of companies manufacturing rockets, planetary probes or other spacecraft. “It would be useful for any aero-entry onto a planet,” said Kaukler.
In other space-related news, there’s Project Blue: The Space Telescope that Will Search for Another Earth.