The European Student Earth Orbiter (ESEO) is a satellite mission of the European Space Agency (ESA), coordinated by an Italian company, Carlo Gavazzi Space. The project is carried out by European student teams, including three Hungarian groups. Two of these groups are developing scientific experiments for the satellite, while the third team is responsible for the Electrical Power Subsystem (EPS). One of the main objectives of the project is to involve students in a space mission and provide them with hands-on experiences, thus educating future space experts for the different fields of space research and technology.
This thesis presents the development of the PD (Power Distribution) board of the EPS. The PD panel connects each subsystem and payload of the satellite to the main energy bus and separates them from the bus, when necessary. The operation of the PD unit is controlled by the command signals received from the PCU (Power Control Unit).
The on and off statuses of the switches are assigned to the two logical states of the signal received at the inputs of the PD panel. The voltage of the unregulated power bus varies between 24V and 33.6V, while the low voltage buses are regulated at 3.3V and 5V levels.
The PD panel measures the currents drawn by each load and, if a failure occurs in any of the subsystems and payloads, it protects the main power bus from overload. The load current, which is different for each load and varies in the range of 50mA to 10A, is measured by a shunt resistor. The 50-100mV voltage drop on the resistor is small enough to keep the energy loss low, even for the maximum current level. The current limits of the switches shall be adjusted one by one, according to the power consumption of the loads.
In case of failure of a payload, the circuit limits the current drawn by the payload to the predefined value. The command signal and the overcurrent signal are used to form an overload signal, which is monitored and processed by the PCU. If the overload still exists after a preset time interval then the load will be disconnected from the main power bus. The electrical design of the PD unit shall ensure that a single point failure will not affect the proper operation of any subsystem.