3D-Printed Rocket Engine Fires Up

Every time I write about the successful 3D printing of load-bearing metal parts, the blog gets skeptical comments like these. I understand -- it all still seems like science fiction sometimes. But this is really happening, as are 3D-printed rocket engine parts that survive multiple 6,000°F hot-fire tests and perform better than welded ones. The latest? Aerojet Rocketdyne has built and hot-fire tested an entire 3D-printed rocket engine.

This isn't the single part we told you about that passed hot-fire tests last year. That was a metal rocket injector assembly that Aerojet Rocketdyne developed with NASA and built with a selective laser melting (SLM) process. Since then, the company has worked on a separate 3D printing project: a Bantam demonstration engine made entirely with additive manufacturing (AM). Also, NASA has released details on some different 3D-printed rocket engine injectors, including the facts that they've survived tests generating a record 20,000 pounds of thrust and have performed equally well or better than welded parts.

Aerojet Rocketdyne says it wants to make booster, upper-stage, and in-space rocket engines more affordable by designing and building a lower-cost engine family. To this end, its engineers are developing the Bantam family of engines to take full advantage of AM. Using subtractive manufacturing processes, the liquid oxygen/kerosene engine would normally comprise dozens of components. Since geometry constraints are far fewer with AM, the redesigned "Baby Bantam" demo engine consists of only three parts: the combustion chamber, a throat and nozzle section, and the entire injector and dome assembly. The team also cut total design and manufacturing times from over a year to just a couple months, while slashing costs by about 65%.

The 3D-printed Baby Bantam demo engine's nickname is due to its 5,000-lb thrust, compared to the 200,000-lb thrust of the Bantam family's most powerful engines. Bantam engines can be adapted to run on a variety of fuels, such as ethanol, methane, kerosene, and storable propellants. The successful hot-fire engine test is part of a long-term project to develop AM processes, design tools, and part fabrication as well as hot-fire testing. Aerojet Rocketdyne has previously said it is working on an integrated AM effort to make possible the manufacture of rocket engine components with SLM.

Meanwhile, NASA has been involved in a program at the agency's Marshall Space Flight Center to make metal engine parts for the agency's Space Launch System (SLS), a next-generation heavy-lift rocket. The main advantages are creating metal shapes with precise mechanical properties and complex geometries and saving millions of dollars and a lot of manufacturing time. Last July, Marshall engineers performed hot-fire tests on single-piece 3D-printed rocket engine injectors for the SLS. They also compared the results with conventionally manufactured parts made in multiple pieces welded together.

NASA said it took just over a month to 3D-print two of these subscale injectors with Inconel steel powder and complete 11 mainstage hot-fire tests, with a total 46 seconds of firing time. The injectors burned liquid oxygen and gaseous hydrogen during the test at nearly 6,000°F. The tests were conducted as part of subscale acoustic testing for the SLS. Compared to traditionally manufactured injectors, the 3D-printed parts performed equally well.

In a recent video, Marshall team leader propulsion engineer Sandra Elam Greene said rocket engine injectors made for a scale model of the SLS for acoustic testing performed the same as or better than welded parts, with no degradation after 20 hotfire tests. These injectors were made in a single piece using SLM 3D printing, eliminating the 32 brace joints and five welds of traditionally made parts. The 3D-printed injectors also cost about half as much and were made in about one sixth the time.

In later tests last summer, NASA said its hot-fire tests at Marshall of a 3D-printed injector made for the agency by Directed Manufacturing generated a record 20,000 pounds of thrust. The complex, subscale injector contains 28 elements for channeling and mixing propellants. It was made in two parts, instead of the conventional part's 115 components, using a powdered nickel-chromium alloy. This part also passed hot-fire tests successfully.

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