[INTERVIEW] Paul Gradl, NASA: New Rocket Technology Enabled by Additive Manufacturing

Ahead of our online event, Additive Manufacturing Advantage: Aerospace, Space & Defense, conference guest Paul Gradl, a principal engineer in NASA‘s component technology development group, discussed his work in aerospace and space engineering.

“Metal AM plays a huge role in rocket engine development and production now,” Gradl stated. The technology significantly reduces the time required for prototyping and testing, enabling rapid iterations. “We can prototype these in a week or two months and put them on the test stand and iterate on that design,” he explained. While not every component may use metal AM for production, its advantages in complexity and performance often make it the best choice.

Over his 20-year tenure, Gradl has been deeply involved in the development of liquid rocket engine components, including combustion devices and turbomachinery.

Gradl highlighted NASA’s early adoption of additive manufacturing technologies, noting their initial use of polymers for prototypes nearly 25 years ago. “One of the first metal printers I was involved with had serial number two back in the early 2000s,” he recalled. Despite initial challenges with metal prints, the technology gradually improved, enabling the production of reliable components. “It took us probably about 10 years before we really started making parts that we were comfortable with,” Gradl explained, emphasizing the significance of stable laser systems that allowed for multi-day builds and successful hot-fire tests in actual rocket environments.

Developing new alloys for aerospace applications, including hydrogen resistance testing

Technology transfer from the space program is evident in NASA’s development of advanced materials, with certain alloys finding applications for additive manufacturing. One example is GRCop-42, an alloy crucial for rocket engine combustion chambers. Gradl detailed its benefits, stating, “We get about a 40% improvement in wall temperatures over more traditional copper alloys, which means higher performance or greater design margin.” Initially developed in the 1980s, GRCop-42’s production was traditionally expensive and challenging. However, additive manufacturing provided a viable solution, allowing NASA to utilize the material effectively. “We see a lot of applications in different types of heat exchangers, in the energy industry, even cooling devices or high-speed computing.” The material, initially developed for rocket engines, demonstrates NASA’s broader societal contributions.

Gradl also stressed the importance of supply chain adoption in new material developments. “Standing up the supply chain is incredibly difficult to make sure that suppliers can produce it consistently,” he said, noting NASA’s leadership in this area. This effort has already seen success with commercial space companies using GRCop-42 in launches, with many more expected in the future.

Gradl also described NASA HR-1, a hydrogen-resistant alloy crucial for sustainable energy solutions. “Hydrogen can embrittle a lot of materials,” he explained, but HR-1 can operate under high-pressure hydrogen without such issues. This material, used in rocket engines, also holds potential for aviation and other energy applications, aligning with the industry’s shift towards renewable energy.

Another innovation, GRX-810, a nickel-cobalt-chrome alloy, offers significant improvements in high-temperature performance. “We get over 1,000 times improvement in creep resistance at temperatures about 1,100°C,” Gradl said. This alloy, while benefiting aerospace, also finds interest from high-tech industries, including racing and land-based turbines.

Designing advanced materials for additive manufacturing

How does NASA approach the task of creating new materials? “We have a clear need. We have clear requirements,” says Gradl. For instance, the hydrogen-resistant NASA HR-1 alloy was developed to meet the demands of the RS-25 rocket engine for the Space Launch System and commercial needs. The development process involves extensive simulations to predict material performance, which has significantly accelerated due to advancements in additive manufacturing.

Gradl explained, “We use a lot of simulation tools to understand the strength and potential fatigue life.” This iterative process, which once took years, can now yield initial results within months. The subsequent stages involve heat treatment characterization, mechanical testing, and practical application in rocket engines, a process that still spans a year or two for full validation.

Addressing the broader impact, Gradl noted the trickle-down benefits to various industries. “We publish a lot of papers on this, provide a lot of technical data,” he remarked, underscoring NASA’s role in enabling broader industry adoption of these advanced materials.

AM enabling the Rotating Detonation Engine

One of the standout applications of additive manufacturing (AM) is in the production of rocket engine components, particularly combustion chambers and injectors. These parts, characterized by extreme thermal gradients and high pressures, benefit immensely from the complex geometries possible with AM. “Additive allows us to make these really thin walls with all these complex coolant channels,” Gradl explained. This capability reduces manufacturing time from months to weeks, allowing for rapid testing and iteration.

Injectors, traditionally assembled from hundreds of parts, can now be manufactured as a single unit, significantly enhancing reliability and reducing costs. “Consolidation of parts is huge,” Gradl emphasized. This approach has not only streamlined manufacturing but also enabled new propulsion concepts.

Rotating detonation rocket engines (RDE) are a significant advancement in rocket engine efficiency. This technology promises a 20% improvement in efficiency over traditional chemical rocket engines. “To be able to gain 20% is really a game changer,” says Gradl. RDE’s function by maintaining a rotating pressure wave within a cylindrical combustion chamber, resulting in superior combustion efficiency and stability, critical in rocket propulsion.

However, RDE’s were long hindered by material and manufacturing limitations, but have now seen significant progress thanks to AM and materials like GRCop-42 and GRX-810. “Within just a few years, NASA has been able to advance this technology, and we’re actually moving to do a larger scale concept engine,” says Gradl.

What is the future of Additive Manufacturing?

Gradl also gave some insights into his perspective on the future of additive manufacturing (AM), emphasizing the need for speed improvements without sacrificing material quality. He stressed the importance of understanding the interaction between parameters and materials to ensure high-quality outputs, suggesting a move towards more in-situ process monitoring and feedback controls.

Gradl underscored the necessity of a systems approach in AM, integrating all aspects of the additive lifecycle—from feedstock and design to post-processing. “We tend to focus a lot on just the build process,” he noted, advocating for closer collaboration between machine manufacturers and post-processing vendors. This holistic view, which includes powder removal, heat treatments, and machining, is essential for producing successful, high-quality parts. “Understanding the inputs, the process, and all the outputs of that process” is essential for advancing the technology, he emphasized.

As demonstrated, advances made here do not solely benefit the space sector. The new technologies and materials developed for space applications are also finding uses in other high-performance sectors, such as automotive racing and energy. This cross-industry application underscores the broad potential of additive manufacturing to revolutionize various fields.

Join our free event to learn more. Register now: Additive Manufacturing Advantage: Aerospace, Space & Defense.

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