A team of engineers at NASA’s Marshall Space Flight Center, Huntsville, Alabama, USA, have developed, hot-fire tested and patented what NASA says is a new wire-based Additive Manufacturing process for the cost-efficient fabrication of rocket engine nozzles. The process, which has been named Laser Wire Direct Closeout (LWDC), uses freeform-directed energy wire deposition.
Rocket engine nozzles operate in extreme temperatures and pressures from the combustion process and are typically complex and expensive to manufacture. However, NASA stated that LWDC technology has the potential to reduce the build-time on engine nozzles from months to weeks.
Rocket engine fuel nozzles are actively cooled, or regeneratively cooled, by the routing of propellant later used in the combustion cycle through cooling channels in the nozzle, preventing the nozzle walls from overheating. The cooling channels are fabricated within the nozzle during manufacture, but must be sealed to contain the high-pressure coolant.
According to NASA, the LWDC process is used to precisely seal the nozzle coolant channels and, at the same time, to form a ‘support jacket’ on the nozzle with the ability to react to structural loads during engine operation. Paul Gradl, a Senior Propulsion Engineer in Marshall’s Engine Components Development & Technology Branch, explained, “Our motivation behind this technology was to develop a robust process that eliminates several steps in the traditional manufacturing process.”
“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.” After Marshall co-developed and patented the LWDC process, Keystone Synergistic (Port St Lucie, Florida, USA), used the technology to fabricate and test a nozzle.
The nozzle was then returned to Marshall where it underwent hot-fire testing, accumulating more than 1,040 seconds at high combustion chamber pressures and temperatures. Having tested successfully, NASA stated that the technology is now being licensed and further commercial applications considered.
“NASA is committed to revitalising and transforming its already highly advanced manufacturing technologies for rocket engines,” stated Preston Jones, Director of the Engineering Directorate at Marshall Space Flight Center. “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.”
As part of the same research, NASA also developed an abrasive water jet milling process and a second arc-based deposition AM process, used to produce a near-net-shape liner within the jet-milled channels. The research project was undertaken through the agency’s Small Business Innovation Research programme, which connects NASA researchers with industry partners to advance manufacturing.
“One of the things I get excited about is advancing and proving out new technologies for our application with industry partners that a private space company can then use as part of their supply chain,” added Gradl. “That was the objective behind some of this – we formulated the concept, worked with external vendors, and now we’re partnering to infuse this new technology throughout industry to improve advanced manufacturing.”