Insights from the experts Part #11 - A Baptism of Fire for AM & Rocketry

3D-printed rockets have been in the news recently, thanks to the (mostly) successful launch of Relativity Space’s first test flight of a rocket built using additive manufacturing.?

Initially scheduled for launch on the 8th of March 2023, the rocket had since been sitting at the LC-16 launch site at Cape Canaveral Space Force Station after multiple aborted attempts owing a string of environmental and technical issues.

Finally, the launch was given the go all clear early on the 23rd of March, and the Terran 1 rocket (consisting of 85% 3D printed components, by mass) successfully took off from the pad. The mission was designed to reach low Earth orbit (LEO) but was unfortunately unable to reach its target.?

It was however, able to survive the most physically demanding portion of the journey, reaching the point known as “Max Q”, where the aerodynamic forces have the most significant effect on the vehicle’s structure. After passing this milestone, the rocket managed to reach an altitude of 134km, before giving up the ghost, so to speak.

So, while the rocket didn’t reach orbit, the mission has at least demonstrated that from a structural perspective, 3D-printed expendable rockets are completely viable.

So why 3D print a rocket, or a satellite, or anything to go into space in the first place?

Read on to find out why additive manufacturing is a game-changer for the space industry.

Mass Fractions

A launch vehicle (or spacecraft) can be divided into fractions based on the mass of the components in question, with regard to the entire mass of the vehicle. Typically, a rocket can be divided into fuel fraction (which is the largest fraction), structural mass fractions of various types, and the payload mass fraction, which is the tiniest part, sitting right on top of the rocket. The payload is generally the part that you want to launch into space.?

Balancing the various fractions according to mission type can result in increased fuel fraction (to achieve further distance) or increased payload fraction (to put more payload into space).

Because rocket fuels haven’t really changed so much (and probably won’t change in the immediate future), the best way to increase fuel or payload fraction is to reduce the structural mass. And this is where 3D printing comes in.

This doesn’t just apply to rockets, but to spacecraft such as satellites, probes, and rovers too. In the case of a rocket, less structural mass means more fuel and more payload. In the case of a spacecraft, less structural mass generally means more sensors can be added to the vehicle. This is why we are seeing an increasing number of strange, organic-looking structures on hardware destined for other worlds.

There are three main ways by which structural mass can be reduced with additive manufacturing.?

Optimized Geometry

The first method involves reducing mass via some form of geometric optimization, such as topology optimization or generative design. In either of these methods, computational engineering methods are used to remove mass from the structure during the design phase and retain mass only where it is needed (i.e. in the load paths).

Reduced Part Count

The second means by which a rocket/spacecraft mass can be reduced is by reducing the part count with additive manufacturing. Traditionally, complex assemblies would need to be fabricated from multiple parts and then mated and fastened together. Thanks to the design freedom allowed by additive manufacturing, space hardware no longer needs to consist of vast assemblies, but can be consolidated into just a handful of parts. This can reduce the number of ancillary hardware components such as fasteners, seals, and gaskets, and has the additional benefit of increased reliability due to a smaller number of potential failure points.

The Aeon 1 engines that powered Terran 1 on its first (and last*) mission consisted of fewer than 100 parts in each engine, thanks to consolidation from 3D printing.

Lighter Materials

Rockets and other space vehicles have largely been manufactured from a mix of metals in the past, and while additive manufacturing can help reduce the mass of metal components by printing fancy, optimized geometric shapes, there isn’t a lot that can be done in terms of creating lighter alloys. Sure, they can now print multi-metal components, but these components tend to have enhanced mechanical or thermal characteristics rather than being outright lighter in weight.

However, continuous composite printing is increasingly being used for fabricating structures (such as satellites), and engineers are being given a lot more design freedom as a result.

Plastics are also becoming more common, particularly as replacements for components that would otherwise be considered as dead-weight.

Reducing Structural Mass

Reducing rocket mass is important for several reasons:

Increased Efficiency:?

Reducing the mass of a rocket’s structure allows for a larger payload to be carried with the same amount of fuel. This means that a smaller and lighter rocket can be used for the same mission, which results in increased efficiency and cost savings.

Increased Performance:?

Reducing the mass of a rocket also improves its performance. With less mass to accelerate, the rocket can achieve higher speeds and go farther, which is important for missions such as deep space exploration.

Safety:?

A lighter rocket is easier to control and reduces the risk of structural failure during launch. This is particularly important for manned missions where the safety of the crew is paramount.

Launch Cost:?

The cost of launching a rocket is directly proportional to its mass. Therefore, by minimizing rocket mass, launch costs can be reduced, making space missions more affordable.

This article was authored by Phillip Keane, an expert in Additive Manufacturing for Aerospace.

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