AEROJET ROCKETDYNE ADVANCES 3D PRINTING TECHNOLOGY IN ROCKET ENGINES

By Michael Molitch-Hou

As 3D printing technology (AM) integrates into a broader manufacturing ecosystem, it must prove its ability to address critical challenges. Over the years, Aerojet Rocketdyne has demonstrated that 3D-printed components can withstand the high-performance environments of rocket engines.

Recently, the aerospace and defense leader successfully 3D-printed an entire copper RL10 assembly. This represents a key step in developing the company’s RL10 heritage rocket for important space missions. However, this component is the latest in a series of 3D-printed rocket parts from the company, potentially changing how critical components are manufactured in the future.

To learn more about this story, ENGINEERING.com spoke with Jay Littles, Director of the Modern Jet Engine Division at Aerojet Rocketdyne.

RL10 Engine

The RL10 rocket engine has been in service since 1963, sending numerous spacecraft into orbit, including New Horizons and Voyager 1, the first spacecraft to reach interstellar space.

As an important heritage product, the company sought to integrate AM technology into the production equation to reduce costs.

The current RL10C-1 model features a complex series of stainless steel tubes hydroformed and brazed together to form the combustion chambers. Aerojet Rocketdyne improved this design by consolidating the parts into two copper components, which were then 3D-printed using laser melting (SLM).

These tubes were replaced by a network of channels designed into larger copper components. As a result, the number of parts was reduced by more than 90%. The entire system was printed in less than a month, cutting months off the main production schedule. Once completed, the chamber underwent a successful hot-fire test. According to Aerojet Rocketdyne, this is the largest 3D-printed copper part to have successfully undergone hot-fire testing.

Littles explained that the copper alloy plays a role in the overall efficiency of the system. The combustion chamber conducts a thermal cycle, where liquid fuel flows through the chamber’s channels—previously made of steel tubes—absorbing heat during combustion and converting it to gas to power the engine turbine. This process is much more efficient using a high-conductivity material like copper.

“From using steel tubes and a much larger chamber, we moved to a shorter chamber made of copper,” Littles said. “We were able to apply interesting AM design features that allow sufficient energy extraction from the chamber to run the production cycle as we have been doing.”

“The RL10 has been in service for a long time, a long history of success, so when deciding to introduce a new technology like AM into such a heritage product, we faced a lot of pressure to ensure we did not affect the stability of the overall system,” Littles added.

“We optimized process and material properties, developed new design curves directly integrated with additive materials, and tested subcomponents, ensuring we had the right inspection processes. The key point is making sure we do not compromise system stability.”

This work represents a major part of the foundational work the company has done with AM. In this context, RL10 is the pinnacle of 3D printing experience to date.

Exploring 3D Printing Technology

Littles noted that the company had been working with AM even before Aerojet Rocketdyne reached its current position and before Pratt & Whitney Rocketdyne was acquired.

About six or seven years ago, in the early days of SLM, the research team at Pratt & Whitney Rocketdyne explored using the technology to build more affordable rockets for two types of engines: high-performance engines, like the AR1 turbocharged engine now in development, and more affordable engines, like the F1 with hot-gas combustion used in the Apollo program.

To determine how AM could impact engine costs, the company designed a 3D version of the F1 hot-gas injector, a method that originally required dozens of components and took one or two years to produce.

Littles explained that the design was printed by an external supplier. “Many people internally were excited because we could do simple things, like producing individual components, instead of building a complex assembly with many small parts that used to take much longer.”

Littles pointed out that, although they could create such a part, some critical areas were still missing. “When we made that component, we realized we inadvertently compromised something else because we created something like an F1 hot-gas injector, a highly complex part operating in a harsh environment.

But we really had no idea how it would function. We didn’t know the physical properties, solidification behavior, or surface effects, or how this part would perform in real-world conditions.”

At that point, the team began additional studies on the missing areas, analyzed material properties, and optimized processes. Over the years, the company addressed these parts by developing standards for new AM projects. For this reason, Aerojet Rocketdyne has recently begun reporting multiple hot-fire tests for 3D-printed rocket components.

“We have design rules and design manuals that inform what we can and cannot do with the SLM process,” Littles said. “We performed component geometry demonstrations, but we are also now at a point where some of the material systems we are working with are ready enough for us to proceed with system validation and production for certain components.”

3D-printed jet engine components

Since the RL10 is a heritage product demonstrating AM quality and reliability, Aerojet Rocketdyne’s 3D printing division also validated other significant AM benefits for rocket engine manufacturing. In 2013, the company successfully tested a hydro- or gas-liquid injector assembly, followed by successful tests on the Bantam demonstrator engine in 2014 and the AR1 engine in 2015.

For Bantam, the engine included three 3D-printed components: the injector and dome assembly, the combustion chamber, and the throat and nozzle. Using AM in this way reduced costs by roughly 65% and cut design and production time from over a year to just a few months.

Regarding the Bantam engine family, Littles said: “Compared to the RL10, the Bantam engines are slightly more open. It’s a broader family, and we are doing many things to change the design. There is a bit more flexibility in what we can do creatively during the development of the Bantam engines we are working on now.”

While the Bantam family allowed Littles and his team more design creativity, the AR10 will allow Aerojet Rocketdyne to shorten design cycles. This is critical because the company needed to deliver the product by 2019. Successfully delivering the engine would help meet the requirements of the 2015 National Defense Authorization Act, which called for replacing the Russian-made RD-180 with a U.S.-produced alternative for national security space launches by 2019.

“With AM, we can create components and get them into tests very quickly,” Littles said about the AR10. “Instead of just analyzing multiple design variants to optimize performance, we can experiment and have empirical data to firmly validate models and shorten the design cycle more than before.”

From the company’s initial AM research, Aerojet Rocketdyne has been able to establish a program that facilitates transferring technology knowledge from one engine to another.

Littles said: “It’s like starting a piece of art. We did some technical analysis and calculations to chart the path for early work. We began using things like energy calculations to make predictions. There are many variables in the process. Not just laser power, but scanning strategy, laser pathing, and geometric requirements. There are many such variables.”

Recently, the company has relied on software via a separate project that allows Littles’ team to optimize 3D printing parameters for efficient iterative part analysis. At the same time, the company is developing domain expertise to apply AM to part design when advantageous.

“We understand which components, systems, or subsystems provide the most benefit,” Littles said, “taking complex assembly components and turning them into one or two parts. Reducing the number of components and labor allows us to identify which parts bring the greatest benefits.”

Although no rocket part has flown yet, Aerojet Rocketdyne has manufactured components in preparation for inclusion in flight systems. The evaluation process for such parts takes considerable time but is critical for systems required to launch rockets into space. In rocket engine manufacturing, any opportunity to reduce cost, production schedules, and manual labor helps.

Source: Engineering.com

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