For over two decades, Paul Gradl, now a principal propulsion engineer, has been inventing solutions to address the challenges of space travel. He started as an intern and now holds five patents – three of which are licensed by commercial industry. His work in additive manufacturing, also known as 3D printing, with a team at NASA’s Marshall Space Flight Center in Huntsville, Alabama, earned the agency’s most prestigious award in 2024, Invention of the Year.
When did you start working for NASA?
I began working with NASA in 2004 at Marshall Space Flight Center. Prior to that, I had internships at NASA’s Glenn Research Center and some time in industry.
Currently, I lead the development of combustion devices and turbomachinery for liquid rocket engines. Our team is responsible for the design, analysis, manufacturing, and testing of these components, including combustion chambers, nozzles, injectors, igniters, and turbomachinery components. We also manage these systems through the entire life cycle, including flight readiness. My primary focus is advancing process development for new materials and additive manufacturing technologies.
In your early days, additive manufacturing for rocket parts didn't exist, so how did you make the jump to something new?
We started with a plastic 3D printer to create prototypes, primarily for flow testing or assessing part fit. These early models were never intended for test stands. Around 2005-2006, NASA acquired an early metal additive manufacturing powder bed machine. While the technology wasn’t mature enough then, its potential was clear, and advancements in lasers and computing soon followed. By the late 2000s, NASA became an early adopter of metal 3D printing, likely among the first to hot-fire test components.
NASA has played a key role in establishing 3D printing as a viable option for aerospace manufacturing. We took significant risks and made strategic investments to mature the technology, enabling rapid design iterations and taking parts through hot-fire testing. While not every effort succeeded, those challenges provided valuable lessons, advancing the technology for the entire industry.
Was it beneficial for NASA to do this?
Absolutely. By taking early risk, NASA demonstrated how additive manufacturing can drastically reduce rocket engine development time, enabling rapid design, testing, and iteration. This approach has been widely adopted by industry and academia. NASA’s success in fabricating complex designs with unique materials has significantly advanced the maturity of additive manufacturing in aerospace.
Today, the launch industry is experiencing tremendous growth, with many new companies emerging thanks to 3D printing's capability to streamline both development and production. Beyond industry, it has become a powerful learning tool for academia. University rocket teams can now produce components in days or weeks, compared to the months or years previously required. This revolution in accessibility is creating new opportunities for the next generation of engineers.
Your team was awarded NASA's 2024 Invention of the Year Award. What impact has this work had in helping you get to this point?
Much of our current work builds on the successful culmination of several projects that proved the feasibility of additive manufacturing. Now, we’re advancing the technology, optimizing it for production and flight applications. The invention from our team integrated multiple techniques, materials, and advanced manufacturing methods, pushing the boundaries of what’s possible.
We developed a large-scale 3D printing process capable of producing fine features in combustion chambers or nozzles at a very large scale — think meters (or feet) in diameter. This innovation allows us to combine multiple materials, enabling the creation of new alloys and optimizing properties like conductivity and strength. Adding a composite overwrap further reduces overall weight.
It took years of iterative design and testing at various hardware scales, with each iteration undergoing hot-fire testing. While there were failures, they provided valuable lessons. We’ve shared this data with industry, and several companies are now testing these technologies in their development engines, with some components successfully flying.
As inventors and civil servants our goal is to see this technology widely adopted, working collaboratively with industry to advance its addition to more flights.
What does it take to be a good inventor?
There is no such thing as an overnight success. What may seem like one usually takes years or even a decade of effort. Patience and perseverance are crucial, whether it’s overcoming funding rejections or convincing others to adopt your ideas. You’ll encounter setbacks — projects that don’t work out as planned or ideas you must scrap entirely. While it can feel like wasted time, those experiences often provide valuable lessons essential for understanding the technology and advancing toward the right solution.
Belief in your ability to solve a problem is important, but so is clarity about the problem itself and the requirements. What is the problem you are actually trying to solve, and will your new solution provide both technical and economic benefits? A strong technical foundation is critical to address the requirements, understand the underlying physics, and methodically prototype and test solutions to meet the environment performance demands.
Communication is equally vital. Great inventors share their ideas openly, inviting feedback — even criticism — to refine their ideas. Holding ideas too closely out of fear of them being stolen can hinder progress. At NASA, I’ve seen ideas thrive and accelerate through open technical discussions, with critical input fostering innovation rather than stifling it.
Finally, persistence is key. Many inventions fail to reach mainstream adoption because inventors stop short of working with industry to ensure scalability and production-readiness. A successful invention requires more than a working prototype — it demands continuous effort to align it with real-world needs and implementation.
Talk about some inventions you've developed that you've been able to take from idea all the way into a licensed patent.
Early on in my career, I helped develop a handheld laser welding system to repair the thin-wall coolant tubes of the space shuttle RS-25 main engine. Working closely with industry, we evolved our invention into a practical product. Since then, many companies have built upon this technology, incorporating fundamental features we developed, including safety systems. The market has grown significantly, with several companies introducing new products.
Another focus has been additive manufacturing technologies for rocket engine components. We've validated the technology through hot-fire testing and licensed several aspects of new materials and processes. However, scaling up and making it production-ready presents a much greater challenge. Industry demands more than patents or papers — they need extensive data packages, including material properties, test results, lessons learned, and lab notes. These comprehensive datasets enable companies to confidently move forward with production.
That sounds like a key component of communication.
Yes, inventions must be accessible, with their nuances clearly understood to ensure success. Publicizing detailed data packages is essential for fostering collaboration and innovation. This is how we see partnerships with industry and universities evolve. It’s an honor when someone says, “We read your paper” or, “We saw your presentation,” knowing our work has helped others build upon and improve the technology.
We’re glad this data is being disseminated through public and NASA platforms, like the NASA Technical Reports Server. An invention limited to a patent application or stored on someone’s computer isn’t truly accessible or fully useful for industry.
You are keeping up your end of sharing information, with over 100 papers published!
I've published over 135 papers on a lot of the technology and materials that were developed over the years. We also wrote a book about metal additive manufacturing. So even though things are not necessarily an invention or patented, I think it's still important that we document that information. As a government organization, we owe that to the public and industry.
What do you find that's most interesting or engaging about the work you're doing for NASA?
I truly enjoy building teams and watching their ideas and designs come to life. Guiding engineers through that development process, asking insightful questions, and mentoring them has been incredibly rewarding. At the same time, being mentored is equally important. No matter how advanced your career, you’ll always have mentors to rely on for guidance.
Collaborating with NASA missions and project offices to integrate inventions and technologies into the programs is deeply fulfilling. NASA’s mission definitely inspires others, and I strongly believe in its goals.
Working with industry offers the unique opportunity to take your invention out of the NASA labs or testing facility and working it into launch vehicles, as well as non-aerospace applications.
Seeing a technology mature to the point where it’s flying and contributing to exploration is the ultimate achievement. NASA’s role is evolving — from leading many direct missions to fostering a thriving space economy. Our knowledge, inventions, standards, and methodologies are critical for advancing commercial space.
We don’t want our inventions sitting on a shelf — we want them actively used in industry. That’s the greatest acknowledgment of our work.
