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Development of a power distribution module for a nanosatellite
The space environment is characterised by harsh radiation, extreme temperatures and vacuum. Electronics subsystems for satellite applications are designed to be fault tolerant and robust enough to survive this environment. A power distribution module (PDM) for a CubeSat nanosatellite application is developed here, with the aim to distribute power to CubeSat subsystems reliably. The PDM prototype is carefully designed with reference to an extensive literature study. The study dwells on the low Earth orbit (LEO) space environment, critically identifying radiation sources and temperature ranges in the LEO. The study further investigates traditional analogue techniques of logic circuit design using bipolar junction transistors (BJTs) which are known for their higher tolerance to radiation sources as compared to recent integrated circuits (ICs). Careful consideration is given to different ways of designing a fault tolerant system. The study specifically looks at redundant circuit design within the limitations of weight and space of a nanosatellite. Possible electrical faults in power systems are identified, which include over-currents, over-voltages, over-temperatures, inrush currents and latchup. This study shows that identified faults generally are overcurrents. A power switch is included in each power distribution channel to trip the current in case a faulty condition is detected. The PDM is designed to have eight power output distribution channels to allow a subsystem load to connect to more than one channel, thereby meeting its power requirements. The PDM power channels are designed identically. Upon application, current limits are selected by a two-resistor divider circuit and connectors are used to connect to a required voltage bus at manufacturing time. The system’s functionality is tested and verified using an Arduino development board interfaced to all I2C devices as a master node, typically the on-board computer (OBC) in a real satellite mission. The system’s functionality in a Gamma irradiated laboratory environment is verified to perform as required. The PDM system is further tested in a temperature cycled chamber from -31°C to 61°C. The system survived the entire eight hour test duration of two cycles. It is observed that the system is fault tolerant to radiation sources up to 10 krad and the temperature limits mentioned. The PDM system is recommended as an additional module to the CubeSat electrical power subsystem (EPS), thereby improving the reliability of the power subsystem. Keywords: CubeSat, power channel, module, radiation, reliability, efficiency, I2C, prototype.