The MASCOT thermal subsystem design is challenging due to the small size of the lander and the multiple requirements for each mission phase. Evaluation of the requirements and trade-off analysis led to assessment of different technologies and approaches, finalized only thanks to a detailed thermal design and analysis phase, an extensive testing campaign, selection of innovative solutions and technologies, development of ad-hoc heat pipe system. After several thermal vacuum campaigns, MASCOT was successfully launched on December 3rd 2014 and it’s currently on its way to the asteroid 162173 1999 JU3