Thermal control of electronics aims to maintain their temperature within the recommended temperature range. Satellite avionics are getting smaller and have a higher power density. Furthermore, the heat transfer modes in space are limited to conduction and radiation, which makes thermal control more difficult. Thermal energy storage materials are a promising candidate for the thermal control of satellite avionics. Solid-liquid phase change materials (PCMs) are latent heat thermal storage materials that store and release thermal energy during melting and solidification. The best method for using the PCMs in thermal control of satellite avionics is PCM encapsulation. PCM encapsulation refers to packing the PCM into a closed rigid container to isolate it from the surrounding. In the present work, a PCM-based heat sink was adopted for thermal control of a small satellite subsystem. The heat sink was made of aluminium due to its relatively high thermal conductivity and was designed based on the outer dimensions of a small satellite subsystem. RT 35, RT 31, and RT 24 were used as the PCM materials, and thermal conductivity enhancers (TCE) with different geometries were used to get over the lower thermal conductivity of the PCM. The present study delivered a transient numerical investigation of the effect of TCE geometry on the thermal control performance of the PCM-based heat sink. Circular pin fins, triangular pin fins, and novel metal foam geometry were used with a TCE volume fraction of 20%. The electronic subsystem was assumed to be "ON" for 10 minutes generating 20W of heat, and "OFF" for 80 minutes. During the cycle, the heat sink's base plate temperature and the liquid fraction of PCM were recorded. The results showed a significant decrease in the base plate temperature when the PCM was used. RT 24 reduced the temperature by about 46% compared to the case without PCM. The lower melting points recorded higher liquid fraction. RT 24 increased the liquid fraction by 27.7%. The results also concluded that the novel metal foam geometry significantly enhanced thermal performance and delivered the lowest base plate temperature.