Development of an Active Thermal Louver for CubeSats Controlled via SMA Actuator

In recent years, CubeSats proved to be valuable resources both for commercial and scientific purposes, leading to a significant technological development in terms of payloads and on-board instrumentation. The employment of more advanced technology usually implies a higher power consumption, and a consequently increased amount of waste heat. The typical, passive thermal control systems currently employed on small satellites, such as paints and coatings, may not be sufficient to guarantee a proper thermal stability, and therefore more elaborate and efficient systems are required. Based on the actuator IRESA (Intelligent Redundant Spacecraft Actuator), under development at the Chair of Astronautics of the Technical University of Munich, a new design for a compact, reliable, active thermal control system for CubeSats is proposed. IRESA is a shape-memory-alloy-based, low-power-consuming, high-force-per-unit-mass actuator embedded on a PCB, compatible with the lateral panel of a 1U CubeSat. IRESA produces a linear displacement of 3.5 mm exploiting the contraction of redundant SMA wires heated efficiently through the Joule effect; the displacement can be converted into rotation, allowing the actuator to operate a variety of subsystems. The presented design for the TCS consists of an external louver moved by IRESA, capable of modifying the emissivity of a small radiator or regulate the power emission from the inner part of the satellite to space. The design of the louver was obtained studying the louvered surfaces employed over the last fifty years in larger satellites and adapting the geometry to the features of the actuator, with the general design driver of a minimum complexity for the assembly. Therefore, a configuration with a single blade was chosen and implemented; like its larger counterparts, it reaches and maintains every angular position between the fully closed and fully open states, performing a 90 degrees rotation; the linear displacement of the SMA wires is converted into rotation by a simple lever principle. The proposed subsystem meets the CubeSat Design Specification in terms of geometry and compatibility with a CubeSat of at least 2U. The subsystem was developed as a master thesis project at the Chair of Astronautics of the Technical University of Munich starting from October, 2018. A prototype was successfully integrated in March, 2019, and good results were obtained during the first functional, vacuum chamber and vibration tests, during which the louver proved to work properly and continuously during the opening and closing procedures, and maintained its structural integrity.