This paper was authored by the University of Rome, Thales Alenia Space, and ESA, some big names inthe space business in Europe and was published in a polymer materials journal in 2021.
The paper starts by stating that in recent years small satellite missions have experienced exponentially increased interest, especially using easily manufacturable or commercial off the shelf components.
Specifically they focused on cubesats where weight is extremely important, since 1 cubesat unit has a maximum mass of 1kg at 10cm3 volume. In the structural subsystem, in order to accomplish weight reduction, two main approaches are possible, changing the design of the structure to use less material, or changing the material. Both are tackled in this paper because these two topics are somewhat intertwined.
Firstly change in the design of structure to reduce material usage. This has in the past decade become available through something called topology optimisation. Topology optimisation works by running a FEM analysis on a structure of a given outline, removing as much material from the design as possible, while keeping the pre-set strength conditions. This often results in organic and alien looking structures, because the process is extremely dissimilar to producing strict and replicable shapes like we are used to doing.
But this all is in theory in a software running FEM analysis. In the real world, it is a lot easier to produce rectangles and other strict geometrical shapes. So the issue we run into is that we can design light and strong structures well and good, but actually producing these complex geometries is extremely difficult.
This is unless we use additive manufacturing, which allows simple layer-by-layer procedures to produce these complex 3d geometries in an efficient way. The use of AM and topology optimisation can yield mass savings of 40 to 70 percent.
But the usual ABS and PLA plastics are not good enough to launch into space, due to limitations such as outgassing and radiation resistance. Thus, this paper explores a space suitable polymer called POLYETHER ETHER KETONE, which is ESA certified for use in space, but its properties when produced by an AM process are not yet widely available. For testing three types of samples were created: BENDING, PULLING, and OUTGASSING samples.
Flexural and tensile tests yielded moduli of about 3GPa, which are lower than, but comparable to the usual injection molded version of the same material.
The main focus however was on the outgassing. Testing was done by introducing the material to a high-temperature vacuum environment, and measuring the mass lost over time. The individual parameters are not too meaningful, but the material passed ESA requirements for a material that can be used for structural systems in space with flying colours, also showing that the outgassing properties didn’t change when 3d printed.
Having reached this result, the authors took a 2 U cubesat as a basis and produced a chassis utilizing everything previously talked about in this paper: topology optimisation to reduce amount of material used, additive manufacturing to realise the resulting complex geometry and finally a space worthy material that could be relatively easily in the AM process.
In conclusion the paper shows the feasibility of applying a polymer material with AM techniques to complete the manufacturing of a space-worthy structural subsystem, paving the way for use in real missions.
Paper: Rinaldi, M.; Cecchini, F.; Pigliaru, L.; Ghidini, T.; Lumaca, F.; Nanni, F. Additive Manufacturing of Polyether Ether Ketone (PEEK) for Space Applications: A Nanosat Polymeric Structure. Polymers 2021, 13, 11. https://doi.org/10.3390/polym13010011
Slides: This was a slideless presentation