Satellite subsystems are becoming smaller and have extra power density. There are only two types of heat transport in space: conduction and radiation, making thermal management more difficult. For the thermal regulation of satellite subsystems, thermal energy storage materials are appropriate. In the present study, small satellite subsystems were controlled using a phase change material (PCM)-based heat sink. The design of the aluminium heat sink was according to the outside dimensions of the subsystem in a small satellite. The PCM material used in the work was RT 35. Integrated fins of various shapes were used to overcome PCM's poor thermal conductivity. Three fin geometries were investigated: parallel fins, cross fins, and pin fins. Three shapes of pin fins were evaluated: square pin, circular pin, and triangular pin fins. The heat sink was exposed to a thermal cycle with 80 min cooling and 10 min heating processes. The results reveal that pin fins have better thermal performance than cross and parallel fins. For pin fins, the triangular pin fin provides the best thermal performance among all cases. Maximum temperatures reported for triangular pin fin were 41.5 °C with a 10.8 % reduction. The results indicated a considerable improvement in thermal performance by increasing the number of pin fins.