3D-Printed Rocket Engines & The Future of Spaceflight
Ian Wright posted on May 30, 2019 |
Testing the 3D-printed Launcher E1-LOXCOOL725 LOX/RP-1 liquid rocket engine, printed with copper alloy and cooled with liquid oxygen. Captured during an oxygen rich transient. (Image courtesy of Launcher.)
Testing the 3D-printed Launcher E1-LOXCOOL725 LOX/RP-1 liquid rocket engine, printed with copper alloy and cooled with liquid oxygen. Captured during an oxygen rich transient. (Image courtesy of Launcher.)

Getting off of this planet isn’t easy, even after we’ve spent more than half a century doing it. In that time, the strategy generally involved going big, like the Saturn V. It’s still a viable approach today—just look at SpaceX’s BFR—but as the private sector space race heats up, aerospace companies are starting to reconsider how they design and manufacture launch vehicles. Metal 3D printing has been one of the principle drivers of this paradigm shift, unlocking new geometries and features that were impossible to  make using more conventional manufacturing methods.

3D-Printing Rocket Engines – SpaceX and The Early Adopters

“Some of the early adopters, like SpaceX, jumped on this bandwagon way back—it’s probably been almost eight years ago—because they saw the potential and actually advertised it,” explained Scott Killian, Business Development Manager for EOS North America. “There were other companies—like Aerojet—and obviously NASA was also looking into this. But I think it was really SpaceX and their model of getting into space quickly that got a lot of visibility for additive in the marketplace.”

This makes perfect sense. Metal additive manufacturing (AM) has exactly what manufacturers producing aerospace components need most: the ability to create complex or otherwise impossible geometries and iterate designs rapidly. It also explains why metal AM is spreading so rapidly in the burgeoning private space launch industry. “There’s this rush now to get into space and everybody’s looking for ways to launch at a lower cost,” Killian observed.

Even with the most advanced manufacturing technologies, cutting costs for a space launch is difficult simply due to the physics involved. “If you think about it,” Killian said, “rocket propulsion engines haven’t really changed a whole lot since they were developed. We’re just now at a point in the past five to eight years of seeing real innovations that haven’t been seen before.”

Obviously, metal 3D printing has played a major role in this development. The fundamentals of rocket design may not have changed, but metal AM has unlocked new ways to improve rocket performance, such as built-in cooling channels.

Test print of the Launcher Engine-1 rocket engine chamber: Without these cooling channels flowing kerosene from the nozzle to the injector, the combustion chamber would melt and destruct in seconds.
Test print of the Launcher Engine-1 rocket engine chamber: Without these cooling channels flowing kerosene from the nozzle to the injector, the combustion chamber would melt and destruct in seconds.

“Being able to design geometries into the part that allow for the engine to cool better gives a huge bump in performance,” Killian said. “You can also take material out of the part that you couldn’t do cost-effectively with traditional methods.” The fact that metal additive manufacturing can reduce costs in this way has spurred the growth of space sector start-ups—a business model that would have been unthinkable just a few decades ago is now a reality.

Killian summed it up this way:

“It’s easy for a company of five people to design parts and get them out to a service bureau to have them built,” he said. “You still have to test, of course, but you can do a lot of the smaller scale testing on your designs before you scale up or go into production. With additive, you can go through five iterations of a design before you’d even get the first ones through a traditional method, and all five of those together will probably cost less than one traditional iteration.”

Launcher is one example of a start-up space sector company, building rocket engines for small scale satellite launches using additive manufacturing.

“I don’t think there would be any start-ups right now doing liquid propulsion if 3D printing wasn’t around—we certainly wouldn’t be,” said Max Haot, founder and CEO of Launcher. “And now we’re getting to the second phase, where we’re reaching the same mix ratio and combustion pressure that you see in the highest performance liquid rocket engines in the world, but for a fraction of the cost, and thanks to the work of AMCM and EOS, we’re starting to creep up in size, too.”

Metal Additive Manufacturing – Types and Build Volumes

It’s easy to be overwhelmed by the slew of 3D printing acronyms: selective laser sintering (SLS), selective laser melting (SLM), direct metal laser sintering (DMLS), powder bed fusion (PBF), directed energy deposition (DED) and electron beam melting (EBM), to name just a few. When it comes to metal AM, the simplest way to delineate the most common technologies is by feedstock, i.e. metal powder vs metal wire. The former category includes SLS, SLM, DMLS and PBF, while the latter includes DED and EBM.

Launcher Engine-1 rocket injector, printed on an EOS M 290 metal 3D printer. (Image courtesy of Launcher.)
Launcher Engine-1 rocket injector, printed on an EOS M 290 metal 3D printer. (Image courtesy of Launcher.)

Although both types of metal additive processes offer benefits that are difficult or impossible to attain with traditional manufacturing methods, there are some key differences between them. Generally speaking, the relative accuracy and precision of powder-based machines tends to be higher than for wire, and parts produced using powder-based technologies tend to be smaller and more complex.

“Our standard commercial machine that’s widely used across industries globally is the EOS M 400, which has a 400mm3 build area,” said Killian. “That has a single laser, but there’s also the EOS M 400-4, which is a four-laser machine. Those are two of the biggest productivity machines out there right now.” A build volume of this size can accommodate many (if not most) production metal parts, but manufacturers can go bigger if they need to. “We have a sister company called AMCM—Additive Manufacturing Customized Machines—that’s built machines that are 450mm x 450mm x 1000mm.”

Launcher’s rocket engine, 3D-printed using a copper-chromium-zirconium alloy. (Image courtesy of Launcher.)
Launcher’s rocket engine, 3D-printed using a copper-chromium-zirconium alloy. (Image courtesy of Launcher.)

Killian added that we’ll most likely see even larger machines in the near future, but also acknowledged the physical constraints on powder-based processes, such as the overall weight of the part being produced and the challenge of laying metal powders consistently across a large area. “The other challenge is that you want more than one laser,” he said, “but multiple lasers make a lot of smoke, so how do you get that smoke off the part bed without it interfering with the other lasers?” In other words, when it comes to scaling up metal AM, it’s not simply as easy as making a bigger machine with more lasers.

3D-Printed Metal Parts – Tolerances and Surface Finish

In an industry where the cost-per-part tends to be high and failures can be catastrophic, engineers may be understandably wary of using new technologies like 3D printing for production. According to Killian, however, EOS machines are more than capable of handling tight tolerances, especially in production environments.

“You’re typically going to get <0.01 tolerances, even across a large part,” he said. “It’s not CNC-machining-type tolerances, but they can hold very tight tolerances, particularly in production processes where you set the machine up to run the same part over and over.” Killian made a similar point about the surface finish of metal AM parts. “I think people have come to understand that this process gives you a certain level of surface finish—probably between 225 and 250 RA—and if you need a better surface, you do some post-processing afterwards. Most machining that’s done to these parts is on the mating surfaces, but you can even use bead blasting or shot peening to smooth the surface out.”

Polished bi-metal rocket engine, 3D-printed using a copper-chromium-zirconium alloy on an EOS M290 metal 3D printer.   (Image courtesy of Launcher.)
Polished bi-metal rocket engine, 3D-printed using a copper-chromium-zirconium alloy on an EOS M290 metal 3D printer. (Image courtesy of Launcher.)

All of this points to the now widely accepted conclusion that 3D printing is not a magic bullet for manufacturing. “People who have adopted additive as part of their strategy look at it as, ‘We’re either designing stuff that we can’t build otherwise, or we’re looking at parts that are very difficult to build with traditional methods.’ Those parts have long lead times because they’re tough to machine or cast, but they aren’t a problem for additive.”

Metal AM & The Private-Sector Space Race

Engineers have been building rockets for over 50 years and 3D printing has been around for more than half that time, and yet for many people these still represent the cutting edge of technology. That’s especially true when they’re brought together. Additive manufacturing enables users to produce complex parts, rapidly iterate designs and produce end-use parts that are downright impossible to make with conventional manufacturing techniques. As metal AM adoption continues to grow in the space industry, observers should expect that the private-sector space race—currently dominated by a few big players—will become considerably more intense in the next decades.

The EOS additive process. (Image courtesy of EOS.)
The EOS additive process. (Image courtesy of EOS.)

“Additive is just a piece of the whole supply chain for rocket engines,” Killian said. “But I think it’s going to be a critical piece. Right now, there are all these start-up companies with much cheaper solutions for getting payloads into space and additive is definitely going to impact that for a lot of people.”

For more information, visit the EOS website.


EOS has sponsored this post.  All opinions are mine.  --Ian Wright.

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