This subsection deals with the generation, storage and distribution of energy for the satellite. To ensure the functionality of the other subsystems, a reliable energy supply is essential. The energy is generated by solar cells on the lateral surfaces of the satellite. A “Power Control and Distribution Unit” (PCDU) is used, which on the one hand charges batteries with the power from the solar cells and on the other hand distributes the power stored there to the other subsystems.
Lithium-ion accumulators are planned for storing energy. Particular importance must be attached to good component properties, such as service life, possibilities for temperature control and protection against overcharging and deep discharging. Only if these conditions are met can the satellite’s energy balance function as planned.
There are commercially available batteries that are specially tested for space travel and meet the requirements of our mission. However, since these are very expensive and ordinary batteries can also be of sufficient quality, it is an option to order a large number of these and select the suitable ones through our own tests.
In order to be able to test the functionality of the developed PCDU and the accumulators in our framework on Earth, a dummy is also to be built, which imitates the properties of the later used solar cells in orbit as well as possible.
In addition to the selection and development of components, the observation of voltages, currents and temperatures is a central task of the energy subsection. For this purpose, appropriate sensors are installed at various positions in the circuits in order to track the operation of the individual components, to check their functionality and to be able to detect problems at an early stage. One example is the temperature of the batteries, which must be kept constant despite large temperature fluctuations in orbit in order not to damage the batteries. However, the recording of raw data also offers good opportunities to reconstruct possible malfunctions or to investigate new questions after the satellite has been launched.
Several solar cells attached to the sides of the satellite will be used to generate energy. Different cell architectures and geometries provide different advantages in terms of efficiency, power and price. For this purpose, we survey the current models on the market, collect the parameters and contact the companies.
The “Power Control and Distribution Unit” (PCDU) on the one hand regulates the voltage generated by the solar cells to a voltage suitable for charging the batteries, and on the other hand transforms the voltage generated by the batteries to the system voltage required by the other subsystems. We are developing the circuitry required for this in cooperation with LibreCube, a team at ESOC that is developing an open-source Cubesat platform. The first tests of the PCDU are planned for early 2020.
Simulation is used to predict the behaviour of the power system and aid design decisions. Influences like the satellite orientation, eclipse times, internal efficiencies, energy production by the solar cells and even power demands for communication with groundstations have to be taken into account to allow an accurate model of the energy balance. The open-source software DOCKS from CCERES with self-written wrapper and attitude simulations is used to analyse the battery charge at all times. Visualizing the results is possible through the use of the additional software VTS Timeloop.
Then why not drop by one of our meetings. Our weekly meeting takes place every Wednesday at 4 pm on our Discord server in the voice channel cs_power. If you have any questions, please feel free to contact the team leader of the Power-Tam, Pascal Sauer.