3D Printed Rocket Engines: The Technology Powering the Private Sector Space Race

This article originally appeared on The Conversation. The post contributed the article to’s Expert Voices: Op-Ed & Insights.

Oliver Hitchens, Ph.D. Candidate, Department of Electrical and Electronic Engineering, University of Surrey

The volatile nature of space rocket engines means that many early prototypes end up embedded in banks of land or decorating treetops that are unfortunate enough for neighboring test sites. In fact, unintentional explosions are so common that rocket scientists have come up with a euphemism for when they happen: Unscheduled Quick Takedown, or RUD for short.

Every time a rocket engine explodes, it is necessary to find the source of the failure in order to repair it. Then a new and improved engine is designed, manufactured, shipped to the test site and started, and the cycle begins again, until the only teardown that takes place is the slow, timed teardown. Perfecting rocket engines in this way is one of the main sources of development delays in what is a rapidly expanding space industry.

Today, 3D printing technology, using heat-resistant metal alloys, is revolutionizing trial-and-error rocket development. Complete structures that previously required hundreds of different components can now be printed in a matter of days. This means that you can expect to see many more rockets exploding into small pieces in the coming years, but the parts they are made of will actually get bigger and less as the private sector space race intensifies.

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Rocket engines generate the energy equivalent to detonating a ton of TNT every second, directing that energy into an exhaust that reaches temperatures well above 3,000 degrees Celsius. Those engines that handle this undisguised quickly in an unscheduled manner take at least three years to design from scratch, most of which is accomplished through the cyclical process of redesign, rebuild, overhaul, and repeat.

That’s because rocket engines are incredibly complex. The Saturn V F-1 engines that launched Neil Armstrong to the moon in 1969 each had 5,600 parts made. Many of them were sourced from different vendors and had to be individually welded or hand-screwed, which took time.

The F-1 rocket engines that launched Apollo 11 toward the Moon were made of thousands of individual parts.

The F-1 rocket engines that launched Apollo 11 toward the Moon were made of thousands of individual parts. (Image credit: NASA / Wikimedia)

This long and expensive process might have been fine in the 1960s, with the US government funneling money to NASA to jump-start the space race, but for private companies it just takes too long.

Add rocket fuel

The key to rapid engine development is reducing the number of parts, reducing the time it takes to assemble the engine and the disruption caused by supply chain delays. The easiest way to do this is to change manufacturing processes. Space companies are now moving away from subtractive manufacturing processes, which remove material to shape a part, towards additive manufacturing processes that build a part by adding material little by little.

That means 3D printing. Increasingly, engineers are favoring a process called selective laser sintering to 3D print rocket engine parts in an additive process. It works by first placing a layer of metallic powder, before melting the shapes into the powder with lasers. Metal sticks where it melts and remains powdery where it is not. Once the shape has cooled, another layer of powder is added and the part is built layer by layer. For rocket engines, an Inconel copper superalloy powder is used as it can withstand very high temperatures.

Selective laser sintering enables in-house printing of various components, as a unified part, in a matter of days. When a RUD occurs and the fault is found, engineers can create a solution using 3D modeling software, integrating highly complex parts into new rocket engines to perform an ignition test a few days later.

The use of 3D printing also helps manufacturers reduce the weight of the entire rocket, as fewer nuts, bolts and welds are required to produce its complex structure. 3D printing is especially useful in manufacturing an engine’s complex regeneratively cooled nozzle, which routes cold fuel around the hot engine to simultaneously cool the engine walls and preheat the cold fuel prior to combustion.

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A redesign of the Apollo F-1 engines using 3D printing reduced the number of parts from 5,600 to just 40. No company has yet reduced this number to one, but it is undeniable that 3D printing has brought with it a new era of rapidity, development of sensitive rocket engines.

Viable business

That is important for private space companies. Building a rocket is not cheap. Investors can get fickle as RUD’s scrap pile begins to pile up. Companies competing to launch payloads into space take a public relations hit every time they are forced to delay their launch schedules due to faulty rockets.

Virtually all rocket startups and space startups are embracing 3D metal printing technology. It speeds up their development phase, helping them survive the crucial years before they manage to get something into space. Notably, Rocket Lab, which uses its 3D printed engine to launch rockets from New Zealand, and Relativity Space, which is 3D printing its entire rocket. In the UK there are Skyrora and Orbex. The latter aims to launch a rocket using a 3D printed motor starting in 2022.

It remains to be seen if a complete rocket, including its engine, can be 3D printed in one piece. But that’s clearly the direction of travel for an industry where complex, lightweight in-house manufacturing will define which payloads go into orbit and which ones end up quickly cloaking at the wrong time.

This article has been republished from The Conversation under a Creative Commons license. Read the original article.

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