If Bryan McEnerney were to write a book, he might name it “Everything you wanted to know about 3D printing with ceramics, but were afraid to ask.” Or maybe not. In 2005, this master of all things ceramic gave his doctoral thesis a less catchy and far more concise title than the one just suggested. “On the Processing, Structure and Properties of Al2O3 – MgAl2O4 Nanocomposites” earned McEnerney a Ph.D. from Rutgers University, a distinguished end to an academic career that includes a master’s degree in ceramic engineering (also from Rutgers) and a bachelor’s in materials science and engineering from Lehigh University.
Today, Dr. Bryan McEnerney serves as a materials technologist for propulsion, thermal, and materials systems at NASA’s Jet Propulsion Laboratory (JPL) in Los Angeles. And after more than two decades of studying and then working with ceramics—first at Pratt and Whitney Rocketdyne (now Aerojet Rocketdyne), followed by what has since become a lengthy tenure at JPL— he has plenty to say about the materials that many of us equate with bathroom tiles and fine dinnerware.
Surprisingly, however, many of the scientific papers he’s either written or collaborated on during that time don’t even mention the word ceramic, focusing instead on more common, high-performance additive manufacturing (AM) materials like AlSi10Mg and polyetheretherketone, or PEEK. That’s because additive manufacturing with ceramics remains quite challenging, McEnerney points out, filled with concerns over part shrinkage, porosity, density, binder materials, and the somewhat ominous term “flaw population.”
“One of the biggest roadblocks with 3D printing ceramics is that most have a very high melting point,” said McEnerney. “For instance, where aluminum melts at 660 degrees Celsius [1220°F], aluminum oxide melts at nearly four times that, or 2,200 Celsius [3992°F]. Also, it has a very high modulus of elasticity, and like many ceramics, is susceptible to thermal shock. That’s why we use Pyrex rather than traditional high-strength ceramics for oven cookware. So even though this class of materials has some wonderful properties, it’s just a pain in the butt to print. You’re basically governed by ceramic’s flaws.”
Despite these limitations, McEnerney continues to try. He’ll tell you that he’s been interested in 3D printing since his college days, and that one of his first projects 22 years ago was an attempt to incorporate ceramic powder into the polymer-based feedstock used in fused filament fabrication (FFF). That project eventually ran out of money, but it did make him a self-avowed champion of additive manufacturing.
Since then, he’s watched as others have achieved limited success with ceramics using binder jetting and stereolithography, although here again, the difficulties of forming fully dense objects free of distortion and porosity are significant. “We’re currently working on a somewhat radical alternative to those traditional approaches, but I can’t really share more about it at this time,” McEnerney said.
Fortunately for McEnerney’s career path, ceramics begin as a powder. Between that and his extensive background in materials science, this makes him an expert in powder metallurgy, a very relevant and sought-after ability in the field of additive manufacturing. It’s materials such as aluminum, titanium, and tungsten, therefore, that he has spent most of his time with, printing parts that are quite literally out of this world.
One example of this is his work on PIXL, an acronym for “Planetary Instrument for X-ray Lithochemistry.” This lunchbox-sized device sits on the end of the Mars Perseverance Rover’s robotic arm, where it measures the chemical makeup of rocks on the planet’s surface and looks for life. McEnerney was the material and process (M&P) lead for the team that designed and built PIXL, which uses 3D-printed front and rear covers, a mounting frame, and supports for the X-ray scanner, all made from AlSi10Mg (aluminum) or Ti-6Al-4V (titanium).
Another of McEnerney’s Perseverance projects was the Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE. Here, a 3D-printed component made of high silicon aluminum and filled with tiny channels converts carbon dioxide-rich Martian air into the oxygen that will be needed to propel future spacecraft back to Earth. “It’s like a fuel cell run in reverse,” he said.
There’s also Cupid’s Arrow, part of the Planetary Science Deep Space SmallSat Studies (PSDS3) program that will use small satellites—or CubeSats—to investigate Venus, Mars, Earth’s moon, various asteroids, and the outer planets. McEnerney was part of the team tasked with developing Additively Designed and Manufactured components for SmallSat Structures (ADAMSS), which in this case will skim the scorching hot, sulfuric acid-filled Venusian atmosphere to collect gases for analysis.
“The Mission Directorate wanted to see if we could use AM to create multifunctional designs, so over the course of two years, we built numerous versions of a teardrop-shaped propellant tank that serves as the primary structure for the spacecraft as well as a housing for a mass spectrometer,” he said. “We ended up with a one-piece design that greatly exceeds the mission parameters for vibration, pressure, and weight, even when using a relatively low strength material like AlSi10Mg [high-silicon aluminum].”
COVID-19 delayed much of the PSDS3 program, so the Venus-bound CubeSats just described are slated for a future launch. Regardless, McEnerney is rightfully proud of what he and his colleagues have accomplished. He noted that manufacturing the propellant tank and similar space-bound components might be possible with conventional technology, but it would be both costly and time-consuming, and there would be far fewer opportunities for design iteration and optimization.
Said McEnerney, “Just to make a casting might require six months or more, and it would not come anywhere close to delivering the multifunctional capabilities possible with AM. That’s why I hope to apply the methodology behind our propulsion module to any extra-planetary craft, such as the JPL Insight lander, where we flew two of the first CubeSats—MarCO-A and MarCO-B—to another planet.”
There will be more such projects. Lots more. Additive manufacturing is already playing a pivotal role in space exploration and will gain an even stronger foothold going forward. Some of that momentum, he said, is thanks to people like Alison Parks, Richard Russell, and others at NASA who (together with McEnerney) collaborated on the space agency’s Standard 6030, “Additive Manufacturing Requirements for Spaceflight Systems,” the document that makes AM material qualification a much less onerous task than it once was.
McEnerney is collaborating on another potentially ground-breaking AM capability: gradient alloys. “We’ve been working with a handful of universities on transitioning from titanium to stainless steel in a single build. It’s been a real challenge because it tends to crack, so we brought in thermodynamic modelers and process path analysis tools and, boxes and boxes of broken samples later, have developed a technique that Penn State will be publishing a paper on very shortly.”
The design iterations he mentioned earlier are also getting easier, thanks to topology optimization and related software tools that make McEnerney’s goal of multifunctional much more achievable. Between that and the development of spaceflight system design standards—not to mention the extensive experience that McEnerney and his counterparts at NASA bring to the table—advanced designs like this will become increasingly commonplace.
Such work delivers an unexpected side benefit. Because 3D printed parts are much less costly to develop and can be deployed in record time, NASA is finding that its return on investment is quite literally skyrocketing. “The SmallSats, for example, are fly-along spacecraft that get launched with one of the bigger New Frontiers or Discovery-class missions,” said McEnerney. “So they get the benefit of piggybacking onto an existing project, for starters, and can get scientific results back in less time because they’re willing to take a little more risk. People aren’t going to complain as much if you lose a $50 to $100 million asset versus one that costs a billion dollars.”
McEnerney is quick to qualify this last point. JPL’s charter, he explained, is robotic exploration of the universe. And unlike human spaceflight, no one will mourn the loss of a craft crewed by droids. “No one’s saying, ‘Hey, let’s throw five years and how many millions of dollars down the drain,’” he said. “But at the same time, we don’t have the budget allotted to a Mars 2020 mission. To give us the biggest bang for the buck, we have to take some risks, albeit in a controlled fashion. Additive manufacturing with its ability to execute on multifunctional designs lets us do just that.”
Design opportunities and cost considerations aside, McEnerney concluded with a statement that should by now be abundantly obvious. “I have a really cool job,” he said. “And speaking for myself and all those who’ve worked with me on these projects, I have to say that it’s gratifying to know we have fully functional, additively manufactured parts doing science on the surface of Mars right now.”
