| Περίληψη: | The scope of this thesis is to design, built and test a Double-Unit nanosatellite, with the view of launching and operate it in the lower thermosphere. The key innovative approach is the design optimization for an actual space mission, creating a hybrid design for the structural subsystem. The new design approach based on both aluminum and composite materials for the structural frame, fulfilling all design and test requirements and successfully delivered and set into orbit, proving the feasibility of the new design.
Initially, the potentiality of building full composite CubeSat structures was explored. Two different designs were created, that met all design requirements and manufactured, using the vacuum bag-autoclave methodology (carbon-epoxy prepreg). Both structures were tested verifying the FEA results and the mass reduction between the new designs and the commercial available structure (CubeSat-kit) was close to 40%. Despite that, these designs proven not feasible, for use in an actual space mission, as no consideration was made for the internal subsystems.
The design optimization, driven by mass-stiffness principles, led to a new “hybrid” design that met all system requirements, considering all the necessary subsystems of a CubeSat mission. Through Finite Element Analysis the feasibility of the new design was proved and this way it could be used in a space mission concerning a Triple-Unit CubeSat having onboard a deorbiting device (FP7-DeorbitSAIL). The author dealt with the design, analysis and manufacturing of the entire structural subsystem of the mission (electronics bus, 3U CFRP panels, and several small parts) following the aforementioned design approach. All structural components were manufactured using a space approved Cyanate-Ester/Carbon prepreg and autoclave methodology and met all design tolerances and mass requirements. The structural system was passed all required tests, withstood the launch loads and set into orbit fulfilling its mission. This way, the first attempt of delivering a flight model (subsystem level) is considered successful as the entire system (and thus the structural subsystem) was labeled as flight proven.
The next step was the designing of a complete space mission (UPSat) from scratch, delivering a fully assembled, fully tested and fully functional Double-Unit CubeSat, under the framework of the FP7-QB50 project. The same design principles as before were followed concerning the structural sub-system, creating from scratch a “hybrid” design using both aluminum alloy and composite materials; the same composite material and lamination was also used for this chassis. The design was based on the use of composite materials as primary structural components, for mass reduction and enhancement of the structural integrity of the entire system and also the ease of access during the assembly and integration procedure. The design of all different subsystems and the assembly management in order to fulfill all design requirements, was one the major difficulties, during the Critical Design Review. Although, the fully assembled CAD model, and the FEA results from the required loading scenarios (Resonance, Quasi-Static, Sine and PSD vibrations, Thermal) passed successfully the CDR phase as the structural integrity and normal operation of all designed subsystems verified.
The entire manufacturing, assembly and integration process took place in Greece and the systems engineering principles applied were in line with the ECSS standards. The author had major involvement and key role during this procedure; assembly and integration sequence, harnessing plan, test sequence etc. The in-house manufactured components met all design requirements, the system assembly performed inside a relatively clean environment, built in-house and all PCBs designed and built according to ECSS recommendations (NO involvement for the author during the PCBs manufacturing and software writing).
The assembled system withstood all required tests, simulating the launch and operational environments verifying the FEA results for an adequately robust CubeSat system. All tests during the vibration campaign (HAI facilities) did not reveal any malfunctions in subsystem level while only visual inspection was performed for verifying the perfect condition of the external components. On the other hand, for the needs of the Thermal Vacuum Campaign, an in-house (AML/UPAT) TVAC chamber designed and manufactured and both tests (thermal cycling and bake-out), verified the normal operation of all subsystems at the extreme conditions the nanosatellite will face during its mission. The UPSat team, completed the FRR phase and got the green light from NASA, NanoRACKS and QB50 personnel for delivering the CubeSat for the final check-out procedures and integration into the P-PODs.
In conclusion, this thesis proved the feasibility of building an entire CubeSat system from scratch; all subsystems were redesigned, built and tested in Greece and met all requirements. The design optimization performed for the structural subsystem led to an innovative design fulfilled all design and system requirements and got the final approval for launch, marked the UPSat mission as the first Greek open-source nanosatellite ever launched.
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