Additive Manufacturing of CubeSats using High-Performance Polymers: Reduce Mass Budget by Up to 50%

Abstract

At the annual 5th European Space Agency CubeSat Industry Day, Orion Additive Manufacturing GmbH presented its ground-breaking technology for the use of high-performance polymers in 3D printing. Because of Orion’s original Thermal Radiation Heating system, the properties of their 3D printed materials have shown drastic improvements compared to ones printed by other technologies. Recent test results have shown that parts printed with Orion’s technology reached up to 80% of injection-moulded PEEK parts’ theoretical strength. This article explores Orion's research that was presented at ESA's CubeSat Industry Day. Orion is demonstrating how cutting edge additive manufacturing technologies and materials can be used to vastly reduce CubeSat launch costs.

Challenges faced during the production of CubeSats

CubeSats are miniature, lightweight satellites used for space research, earth observation, telecommunications, and a wide array of other purposes. Typically, they have a lifespan of a few years before being decommissioned by letting them burn up in the atmosphere upon re-entry. They are produced in low volumes, are of very high value, and often highly customized to their application. Since CubeSats pose little to no harm to human wellbeing, they are part of an industry that is not highly regulated and therefore allows for a lot of customization and innovation. To ensure CubeSats will not negatively affect other satellites or hardware, both during launch and while in space, quality CubeSats adhere to a strict set of design specifications such as those originally published by Cal Poly SLO. This also limits the size and weight of CubeSats.

Traditionally, the frame enclosing a CubeSat is made from aluminum; one of the lightest materials suitable for space. Weight is a very important factor in the CubeSat industry, as launch costs are determined mostly by weight rather than volume. Compared to polymers, aluminum is relatively heavy, and disintegrates slower and produces more volatile space debris when the CubeSat is decommissioned. 

Frames made from high-performance polymers, such as PEEK are more desirable alternatives to aluminum frames due to their lightweight, low-density properties and high strength-to-weight ratio. However, these polymers are often very expensive, especially when considering the waste produced during traditional manufacturing. Like aluminum frames, these PEEK alternatives are created using CNC milling and machining. These are subtractive processes where a lot of material needs to be removed to cut the desired shape out of a block of raw stock material, creating expensive waste. In addition to wasting resources, these traditional manufacturing methods face other limitations as well: parts can only be completely solid, have limitations when it comes to detail depending on the available tooling, and the process is not ideal for the creation of many variants or small batches, since the machines used need to be reconfigured for every different part.

An alternative method for using high-performance polymers is 3D printing, also known as additive manufacturing. For the production of CubeSats, the “Fused Filament Fabrication” (FFF, also known as FDM) method is the most promising, even though there are a number of other popular additive manufacturing methods available, such as Selective Laser Sintering (SLS). FFF processes can manufacture a variety of parts using a wide range of thermoplastics, including PEEK, ULTEM, or PC, with very little waste. This is an important distinction from SLS, which is often wasteful with raw resources and the material choice is much more limited. 

Until recent technological advancements, using an FFF process to produce high-quality parts out of these high-performance polymers was quite difficult. Many additively manufactured parts, especially those made from PEEK, often suffer from “delamination”. This means that the fused layers that build the final shape are not properly welded together. These faulty PEEK parts behave more like a stack of loosely connected slices than as a continuous whole. These uneven mechanical properties are referred to as “anisotropic properties” and are a common problem in printed parts from many manufacturers. 

Opportunities to improve using Additive Manufacturing

Because each production method requires its own approach to part design, it is often difficult to simply print CubeSat parts that have been designed for traditional manufacture. However, using additive manufacturing does offer some unique freedoms. Especially using FFF, parts can be much more complex, and can be hollowed out. Often, existing parts can also be combined into one, reducing complexity and simplifying assembly. A nice example of this is the ‘kill switch’ found in CubeSats, which ensures the device is not  functional until it has been launched. Currently, this is a complex assembly of multiple aluminum frame components, a switch, spring, and plunger. Using the design freedom allowed by the FFF process, this can be reduced to a standard switch with a roller, mounted to a single frame part.


Multiple frame components are needed
The switch, spring, and plunger assembly

The new design, with a switch integrated into a single printed part
In addition to reducing complexity, more weight can also be saved by leaving parts of the component hollow. The material on the outer sides of a part is the most crucial to providing the necessary strength, whereas the inner material merely provides a way for those walls to connect. Removing most of that inner material is a great way to reduce material use and part weight, and is easy to do with FFF processes. Where, for instance, SLS-made components require either one open side to the cavities, or require the parts to be fully dense, FFF processes allow parts to fully enclose hollow shapes. The resulting air pockets do not produce issues when using these parts in space; after all, foams are often used on spacecraft as well. 

The most significant reason for the anisotropic behavior of 3D printed components, delamination, is due to poor bonding of the layers that make up these components. In contrast to other technologies, Orion’s Thermal Radiation Heating system fuses the layers together. This new technology heats the entire object and directs thermal radiation to the previous layer before new material is deposited. Every layer of the printed material is moulded to the previous one with selective heating up to 300 °C. This ensures that the layers form one strong and continuous part. It produces stronger, more isotropic 3D printed components that are ready for immediate use. 

A 3D Printer for Space

When the design techniques and printing technologies outlined above are combined, both the mass of a CubeSat’s frame and its complexity can be drastically reduced. In collaboration with German Orbital Systems, who design and build aluminum CubeSat frames on a regular basis, Orion’s engineers were able to reduce the mass of the frame by 50% while maintaining the same stiffness and surface quality. Considering the costs of launching such a satellite, this amounts to about €25.000,- in savings per launched CubeSat, or allows for heavier contents within the 1.33kg limit per CubeSat. 

This is made possible by Orion’s Thermal Radiation Heating system, because its unique technology creates superior inter-layer bonding strength. External testing has shown that the tensile (pulling) strength of standard 3D printed testbars was increased by more than a factor of 4. The tested PEEK material samples achieved an ultimate tensile strength of 72MPa; about 80% of the theoretical strength of PEEK!

To ensure that the printed CubeSat parts would survive in space, parts printed using Orion’s A150 machine were tested at the ESA-ESTEC laboratories. A simulated space environment exposed the printed components to an UV exposure, equivalent to 3,4 times the solar constant, and vacuum, similar to what CubeSats experience every day. This was followed by thermal vacuum cycling, switching between -100°C and +100°C. Even after exposure to these simulated space challenges, there was little to no change in the material properties of the parts, and the components remained functional.

Conclusion

Using a cutting edge additive manufacturing process with Orion’s Thermal Radiation Heating system, it is possible to reduce the mass of a CubeSat’s frame by up to 50%, while maintaining the same strength and adhering to the same tolerances and requirements as more traditionally produced components. Parts manufactured this way have proven to withstand the challenges of space, and can reduce the launch cost per CubeSat by up to €25.000,- or can lead to larger freedom in payload selection and weight without compromising functionality, launch cost, nor safety, because of the highly isotropic properties of components printed using Orion’s Thermal Radiation Heating system. 



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