3D-printed rocket engines: The technology driving the private sector space race

This article was first published by The Conversation. Space.com's Expert voices: Op-Ed and Insights was contributed by the publication.
Oliver Hitchens, Ph.D. Candidate, Department of Electrical and Electronic Engineering University of Surrey

Many early prototypes are stuck in dirt banks and end up decorating tops of trees. This is due to the volatile nature of space rocket engines. Rocket scientists have devised a way to describe unintentional explosions, called rapid unscheduled destruction (or RUD).

Each time a rocket engine explodes, it is necessary to identify the cause. The new engine is then manufactured, sent to the test site, fired and then the cycle continues until the last disassembly is completed. This is how the space industry is developing its rocket engines.

3D printing technology is changing the way we develop rockets through trial-and-error. It uses heat-resistant metal alloys. In just days, whole structures that used to require hundreds of components can now be printed. As the private sector space race intensifies, you can expect to see more rockets breaking down into smaller pieces over the next few years. However, the parts that they are actually made of will become increasingly scarce.

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Rocket engines produce the equivalent of releasing a tonne worth of TNT per second. They then direct that energy into an exhaust temperature of well over 3,000°C. It takes at least three years to build an engine from scratch that can do this without disassembling in an unscheduled manner.

Rocket engines are extremely complex. Each of the 5,600 parts that made Neil Armstrong's 1969 rocket to the moon with F-1 Saturn V engines had 5600 each. Many of the parts were from different suppliers so each one had to be individually welded and bolted together manually. This took time.

F-1 rocket engines were constructed of thousands of parts that enabled Apollo 11 to launch towards the Moon. Image credit NASA/Wikimedia

In the 1960s, this lengthy and expensive process was fine. The US government provided money to NASA to fund the space race. But for private companies, it is too slow.

Rocket fuel can be added

Reduce the number of components is key to speeding up engine development. This reduces the time required to assemble the engine, and reduces disruptions caused by supply chain delays. Modifying manufacturing processes is the best way to achieve this. Space companies are moving away from subtractive manufacturing, which involves removing material to form a part, to additive manufacturing processes, which build up the part by adding material bit by bit.

This means that 3D printing is possible. Engineers are increasingly using selective laser sintering to create 3D printed parts for rocket engines in an additive process. The process involves first coating the metal powder and then melting the shapes with lasers. The metal will bind to the areas it has melted and remain powdery where it is not. After the shape is cooled, another layer is added of powder and the part is assembled layer by layer. Because it can withstand extremely high temperatures, Inconel copper superalloy powder is recommended for rocket engines.

Selective laser sintering makes it possible to print multiple parts in-house as one part in just days. Engineers can fix a RUD using 3D modeling software. They can also integrate complex parts into new rocket engines that are ready for testing firing within days.

3D printing helps reduce the overall weight of the rocket by requiring fewer nuts, bolts, and welds to create their intricate structure. 3D printing can be used to create complex engines with a regeneratively cool nozzle. This route cool fuel around the hot engine to cool it and then heat the fuel for combustion.

The single-piece rocket thrust chamber, which will be on display at #ParisAirShow in Hall 2C Booth C354, is a reduced assembly component that includes integrated cooling channels and internal ducts. https://t.co/x7JddUk4yl pic.twitter.com/Q1WnErNs07June 19, 2019 See more

The number of parts required to redesign the Apollo F-1 engines was reduced from 5,600 down to 40 by 3D printing. Although no company has yet to reduce the number of parts to one, it is clear that 3D printing has enabled a new era in rocket engine development.

Viable business

This is important for private space companies. It is expensive to build a rocket. As the RUD pile grows, investors may become feisty. When companies are forced to delay their launch dates due to faulty rockets, it can be a serious blow to their public relations.

Virtually every new space startup and rocket company is using 3D metal-printing technology. It speeds up their development and helps them to survive the critical years before they can get into space. Rocket Lab uses its 3D-printed engine for rocket launches from New Zealand and Relativity Space 3D prints its entire rocket. Orbex and Skyrora are two of the UK's most prominent 3D-printed engines. This latter group aims to launch a rocket with a 3D-printed engine by 2022.

It is still to be determined if a complete rocket, including its engine can be 3D printed in one piece. This is clearly the direction of travel in an industry where light-weight, complex and in-house manufacturing will determine which payloads are placed in orbit and which ones end up disassembling at an inopportune time.

This article was republished by The Conversation under Creative Commons. You can read the original article.

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