Designing, Implementing and Testing the Solar Power Harvesting System for ESTCube-1
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Estonian Student Satellite project started in the summer of 2008 at Tartu University with the objective for promoting space and giving students a hands-on experience on developing space technologies. The main outcome of the project was pronounced to be a fully operational picosatellite ESTCube-1 - the first Estonian satellite. The goal of ESTCube-1 satellite is to deploy a single 10 meter long Hoytether in low Earth orbit using a centrifugal force. The success criteria for this objective is the deployment of the tether and the snapshot of the visual confirmation of the deployment. The successful tether deployment is needed to demonstrate technologies for a full-scale Electric Solar Wind Sail (ESAIL) test mission in the future. The concept of ESAIL has potential to become one of the most efficient space propulsion technologies in the history. ESAIL is based on the interaction between the positively charged particles in the solar wind with the positively charged tether net deployed from a satellite. Each tether is a fourfold Hoytether structure to be as light as possible, but to maintain the durability needed in the harsh space environment. The concept was proposed by Pekka Janhunen from Finnish Meteorological Institute (FMI) in 2006. The concept of ESAIL has potential to become one of the most efficient space propulsion technologies ever invented. ESTCube-1 Electrical Power System (EPS) is responsible for gathering power from solar panels, storing into batteries and distributing it to the whole system.The main goals of the current work were to: analyze solar panels characteristics and solar power harvesting concept; analyze the concept of Maximum Power Point Tracking (MPPT); analyze requirements for solar panel controller; propose a solar panel controller design for ESTCube-1; develop a solar panel controller prototype; test the algorithm of MPPT; test the efficiency of solar power harvesting. The work consists of eight Chapters. The Chapter 3 gives a more detailed overview of ESTCube-1 satellite with focus on EPS subsystem. Chapter 4 analyzes the concept of solar power harvesting and the need of MPPT. Also the general characteristics of solar cells are analyzed and the simple model of solar cell work is pointed out. Chapter 5 proposes the design layout of solar panel controller, the implementation of MPPT algorithm and the implementation of solar panel controller software. Based on the design layout, the solar panel controller prototype development with measurement analyzes are described in Chapter 6. Chapter 5 and 6 form the main body of the work. In Chapter 7 the future activities are proposed and in Chapter 8 most important results are concluded and the completion of goals is assessed.