Micro Louvers Based On Thin Film Technology For Satellite Application

All spacecrafts and the instruments they support require an effective thermal control mechanism in order to operate as design and achieve their expected lifetimes. The traditional approaches to spacecraft thermal control involves large radiators connected to the spacecraft by heat pipes, large and bulky thermostat controlled louver structures and power hungry heaters. These approaches are not effective for small satellites below20kg, so-called micro and Nano-satellites. Micro satellites with much shorter design cycles and fewer resources, volume, and surface, require an active approach. Commonly used active methods such as electric heaters, heat pipes or mechanical louvers incur additional electric power requirements, weight, and bulkiness to the system. Now, more flexible approaches are desired to address these issues. One solution is using micro louvers to actively adjust the exposed area of high emissivity radiator to the space. Micro-louvers, which based on MEMS manufacture process and actuated by electrostatic, have some more attractive characteristics such as small volume, low weight and less power consumption. It can adjust its equivalent emissivity according to the actual thermal environment, and quite meet the requirement of micro and nano satellites’thermal control.In this paper, a polyimide based micro louver is developed. The device structure was designed, the actuation voltage was analyzed theoretically and fabrication process was described. The main parameters were tested and results were presented. A large area suspended thin film, which with5μm average thickness and contains1029elements in40mm square, was successfully prepared by dipping coating method. The micro structures were micro machined by UV excimer laser micromachining process. The thin film stress in micro-louvers for spacecraft was basically studied. By studying the basic theory of thin film stress, the mechanism of stress in flexible film of Al/PI is discussed. The controlling technique of stress is achieved which includes changing deposition parameters and rapid thermal annealing. The test results show that the equivalent emissivity variation of micro-Iouvers was0.43and the actuation voltages were varied from360V to922V.