Rocket engine nozzles operate in extreme temperatures and pressures from the combustion process and are complex and expensive to manufacture.

That is why a team of engineers at NASA’s Marshall Space Flight Center in Huntsville, Ala., developed and proved out a new additive manufacturing technique for nozzle fabrication that can greatly reduce costs and development time.

A new process called Laser Wire Direct Closeout was developed and advanced at NASA to build a less-expensive nozzle in significantly less time. LWDC is a different process than most 3-D printing technologies, which are powder-based and fabricated in layers. It uses a freeform-directed energy wire deposition process to fabricate material in place. This new NASA-patented technology has the potential to reduce build time from several months to several weeks.

“NASA is committed to revitalizing and transforming its already highly advanced manufacturing technologies for rocket engines,” said Preston Jones, director of the Engineering Directorate at Marshall. “What makes this development project even more unique is there were three separate, state-of-the-art, advanced manufacturing technologies used together to build a better nozzle and prove it out through hot-fire testing — an example of why Marshall continues to be a worldwide leader in manufacturing of propulsion technologies.”

NASA photograph by David Olive

Through hot-fire testing at NASA’s Marshall Space Flight Center, engineers put this nozzle through its paces, accumulating more than 1,040 seconds at high combustion chamber pressures and temperatures. Now, this technology is being licensed and considered in commercial applications across the industry.

Nozzles may look simple from the outside, but they are very complex. The new LWDC method employs a wire-based additive manufacturing process to precisely close out the nozzle coolant channels, which contain the high pressure coolant fluid that protects the walls from the high temperatures a nozzle must withstand.

Nozzles are actively cooled, or regeneratively cooled, meaning the propellant later used in the combustion cycle is routed through the nozzle to properly cool the walls so they do not overheat. To regeneratively cool the nozzles, a series of channels are fabricated within the nozzle, but then must be closed out, or sealed, to contain the high-pressure coolant. The new patented process using the LWDC technology closes out the coolant channels and forms a support jacket in place, reacting structural loads during engine operation.

“Our motivation behind this technology was to develop a robust process that eliminates several steps in the traditional manufacturing process,” said Paul Gradl, a senior propulsion engineer in Marshall’s Engine Components Development & Technology Branch. Gradl has focused his whole career on rocket nozzles and combustion chambers, like this one developed and patented at Marshall. “The manufacturing process is further complicated by the fact that the hot wall of the nozzle is only the thickness of a few sheets of paper and must withstand high temperatures and strains during operation.”
 

NASA photograph by Emmett Given

Engineers from NASA Marshall Space Flight Center’s Propulsion Department examine nozzles fabricated using a freeform-directed energy wire deposition process. From left are Paul Gradl, Will Brandsmeier, Ian Johnston and Sandy Greene, with the nozzles, which were built using a NASA-patented technology that has the potential to reduce build time from several months to several weeks.