Apophis is a well-known Near Earth Asteroid (NEA) that, on April 13, 2029, will experience a close encounter with the Earth. Since it will pass at a distance of approximatively 32000 km from the Earth, this event offers a unique opportunity to study the effects of gravitational interactions on medium-sized asteroids. The European Space Agency (ESA) has announced the RAMSES mission, a satellite equipped with scientific payloads to analyse Apophis’ surface composition and its potential changes during the flyby The present thesis focuses on the preliminary thermal analysis of a microsatellite, based on the concept of the ESA RAMSES mission. The study involved learning to use the Thermal Desktop software, conducting a literature review on thermal control strategies and existing architectures, developing a thermal model, defining mission scenarios, performing a series of thermal analyses, and implementing a thermal control hardware design with validation of the results.