Micro-Mechanically Pumped Fluid Loop CubeSat Design Justification

To date, telecommunication and internet network are dominated by big-sized GEO satellites: several tons in mass and several kW in power demand. They are equipped with heavy and complex thermal control systems. Thermal control systems (TCS) are in charge of temperature control inside the satellite, ensuring that all components and devices stay in their operational (or survival when not working) temperature range. Due to the massive quantity of heat dissipation, active thermal control systems (ATCS) are used; their thermal handling capabilities are superior to those of passive thermal control systems (PTCS). Two-phase mechanically pumped fluid loops (2ΦMPFL) are among the most efficient ACTS. Thanks to the phase change of the working fluid, heat absorption capacities are greater than single-phase loops. Today, a transition towards small-sized satellites is occurring: nano and microsatellites below 100 kg. MEO and LEO orbits become fairly populated by those satellites: small and high-powered. Smaller satellites allow an important decrease in launch and production costs, therefore being more and more preferred. In addition, payloads become smaller and more powerful. Heat dissipation density of electronic devices on board is constantly growing: 30 W/cm² in the past decade, 100 W/cm² today and several hundred in the next years. The increasing power demand and the reducing satellites dimensions need the development of a new generation of active control systems: lighter, cheaper and more efficient. This study aims to give a first overview and guideline on this kind of systems. The feasibility of a micro-mechanically pumped fluid loop is here addressed, and a first concept design is proposed. Goal of the project is to conceive a system capable of handling 100 W of thermal power on a 1U-CubeSat. Astounding performances are achieved using micro-scale heat transfer: flow boiling and condensation heat transfer coefficients sharply increase in microchannel geometry. Firstly, the state of art on flow boiling and condensation is resumed, then, two-phase pressure drops, heat transfer and critical heat flux correlations are compared to choose which better fits present conditions. Evaporator geometry and fluid type are accurately selected, thanks to an optimisation method present in the literature, (Qu & Mudawar, 2005). A deeper analysis of the micro-2ΦMPFL is discussed in chapter 8. The following chapter is dedicated to the issue of the start-up transient of the system and the pump choice and its characteristics. Last chapters address some of the main sub-systems that the satellite should include, differently to what is done on today CubeSats. Finally, power, mass and costs budget are estimated and some suggestions for future works and the conclusions are presented.