Adaptable CubeSat Structure for Additive Manufacturing

grabcad

Our 3D printed CubeSat structure takes advantage of recent developments in additive manufacturing to provide a simplified design, ideal for customisation to suit a range of CubeSat payloads and purposes. We believe it is inevitable that plastic structures produced by fused deposition will eventually find their way into orbit, due to their ease of accessibility for students, hobbyists, and start-ups alike, and thus we embarked on this project as a study of potential design ideas and capabilities. We have prototyped a variant of this design, which required modification due to the capabilities of 3D printing facilities available to us, and a range of validation tests are ongoing. Our structure is designed for production from high tensile-strength plastics (such as PEEK), though initial prototypes have been created from VeroWhite due to its availability at the Sydney Invention Studio. Depending on the results of future testing, where significant challenges still remain in the analysis of material strength, out-gassing, and resistance to the orbital radiation environment, a pivot towards metal-based production may be pursued, in which case the design could be further cut-down to eliminate unnecessary material. A more comprehensive analysis of the structure we have designed for The Cubesat Challenge is available in an attached document. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Design Features and Advantages Our structural design includes a range of advantageous properties, which allow it to build upon and extend existing CubeSat technologies: - Additive manufacturing with plastics is both fast and inexpensive, allowing rapid prototyping and design iteration, particularly important for student teams and startups where agile development and major design pivots are common. - PEEK and Nylon provide substantially reduced density in comparison to traditional metal-based structures, whilst only requiring minor thickening to make up for their inferior strength properties, meaning overall mass can be reduced substantially. - Our design can accommodate standard PC104 system boards, allowing existing technologies to be integrated, thus reducing CubeSat project development and production costs. - Additive manufacturing allows varying material thicknesses to combat localised stress concentrations, which in our design means stronger support for vertical rails, and tapered thicknesses on end faces to provide superior strength near PCB mounting points. - Our structure builds upon industry experience and flight heritage, implementing face patterns known to provide good strength characteristics, which have been modified substantially to account for inferior strength properties of plastic materials. This design provides a thin entirely external enclosure, maximising the interior space available to components by eliminating cross-beams. - The structure is printable in only two pieces, a main body and upper face, improving strength and simplicity, requiring only four fasteners, and all the while still allowing easy access during prototyping and testing. - Due to the absence of cross-support beams, the detachable upper face could in future be entirely eliminated, allowing printing of the entire structure in a single piece around internal components, further enhancing strength and eliminating fasteners entirely. - 3D Printing allows CubeSat-required components, such as kill-switches and separation springs, to be inserted into the structure whilst it is being printed, allowing refinement of their design to reduce size, mass and complexity. - The design is easily customisable, allowing modification to suit the payload of individual end-users, exhibited by adjustments for inclusion of an LCD screen installed for our prototype satellite’s “selfie” system. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Testing and Future Work Though application of fused deposition with plastic materials to produce a CubeSat structure has many advantages as outlined above, concerns remain regarding in particular the resilience of the material to the launch and orbital environments. This means our design must address concerns which range from outgassing (constrained by the CubeSat standard), to strength properties both during launch and after material degradation due to the orbital radiation environment. We aim to assess these difficulties by an array of tests, which begin in the week following this competition’s deadline with the launch of our prototype CubeSat in the 2015 Intercollegiate Rocket Engineering Competition, in partnership with the Missouri University of Science and Technology. Their HPER design team’s rocket will take our CubeSat up to 25,000 ft, reaching speeds in excess of Mach 1.5. This will allow us to assess our structure’s capability to withstand actual launch stresses, via inspection for deformity and damages after landing, and by collection of data during the launch by on board instruments including strain gauges. Tests of our present build material (VeroWhite) are also ongoing. Outgassing tests are being performed in the University of Sydney’s Space Engineering Department vacuum chamber, which includes a mass-spectrometer for composition analysis. The resilience of the material to radiation exposure will also be determined, by the irradiation of structural components and subsequent strength testing. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Other Resources: Our team has been interviewed on the Australian Broadcasting Company (ABC) Radio National’s Science Show: http://www.abc.net.au/radionational/programs/scienceshow/syd-uni--team-prepares-for-blast-off-in-utah/6507108 Missouri S&T’s HPER Design Team: http://aavg.mst.edu/hper-team/