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STS (Structural Subsystem) |
| The structural subsystem (STS) is split up into the structure and the Solar panel. The structure makes use of a commercial solution, while the Solar panel structure is a custom design. |
The Delfi-C3 structure is based on the 3-unit solid chassis from Pumpkin Inc. in the United States of America. This company provides commercial CubeSat kits including among other things a structure and computer. A 3-unit CubeSat has a total structure length of 326.5 mm and a cross-section of 100x100 mm. The total length of the satellite is 340.5 mm, the extra length is from support feet at both ends (top and bottom). The function of these support feet is to keep the 1-unit CubeSats separated from each other in the P-POD and to house separation springs. The STS is built up out of two main subsections: the primary structure and the secondary structure.
The primary structure consists out of the tube chassis and the top and bottom panels. Together these components absorb the mechanical loads during launch and provide the electrical ground because the primary structure is a Faraday cage. The primary structure components are made from Aluminum 5052-H32 and are alodyned, the P-POD contact surfaces have been hard-anodyzed. The CubeSat kit primary structure cannot be used as is, several modifications are required to facilitate the mounting of other subsystems of the satellite. The modifications to the tube chassis are limited, only slots for external cabling is added. An access hole was investigated, but the CubeSat design did not allow for this. The modifications the top and bottom panels are much more invasive and require new integrally milled panels. The modifications entail a mounting hole for the autonomous wireless Sun sensor (AWSS) from TNO and holes for the four modular antenna boxes (MABs). A stiffener is added to the design of the panels to limit the displacements of the panels, due to the extra mass of the AWSS.
The secondary structure supports the PCB stack inside the primary structure. It consists out of four threaded rods that run the full length of the structure that are connected to all three the components of the primary structure to increase the rigidity. |  |
The Solar panel structure is a segmented design, mainly to minimize the mass and optimize the overall performance during the launch phase. The main section or substrate of the Solar panel structure supports the GaAs (TEC1) triple junction Solar cells and a separate frame located at the end of the panel suspends the thin film Solar cell (TFSC) payload. The Solar panel is 326.5 mm long and 77 mm wide along the TFSC frame and about 5 mm high.
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The TEC1 substrate (referring to the cells that it supports) is made from carbon fiber reinforced plastic (CFRP), more specific 20 plies of unidirectional tape M55J in different orientations. The TEC1 substrate is 1.25 mm thick, this includes a Kapton layer to electrically isolate the Solar cells from the conductive CFRP. The substrate has two mounting points to fix it to the hinge and two mounting points to fix the TFSC frame to the substrate. Two small holes are located at the end of the substrate to thread the hold down wire through.
The TFSC frame is made from Titanium Ti-6Al-4V, similar to the base layer of the TFSC. This gives it almost the same thermal characteristics as the Solar cells and should prevent the TFSC from bulging. A Kapton layer is put on the TFSC frame as a precaution if excessive bulging does occur. The frame also has a large hole to give access to the external connectors on the structure. |  |
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