This thesis addresses the development and optimization of a Regenerative Fuel Cell System (RFCS) for lunar missions, a project initiated by the European Space Agency (ESA) with design and implementation contributions from Thales Alenia Space Italia (TAS-I), the Centre for Research and Technology-Hellas (CERTH), and the Foundation for Research and Technology-Hellas (FORTH). The RFCS is designed to offer a sustainable solution for energy storage and provision on the Moon by leveraging water electrolysis and fuel cell technology to navigate the long lunar nights. Central to this research is the focus on the Thermal Control System (TCS), the Water Management System (WMS), and the avionics architecture.