CubeSats and the space environment poses uniques, challenging and multiphysics constraints on the antenna design. In this work, we present the design of a patch stacked antenna working across the up- and downlink Ka-bands. The selection of the materials and geometry of the radiator was carried out by accounting for the trade-off between electromagnetic, thermal and mechanical requirements. The design of the antenna is performed with a particle swarm optimization algorithm developed to control the bandwidth and matching of the antenna over the Ka-band. Furthermore, a multiphysics thermal analysis is performed to verify the operational stability of the optimized array, mounted on a 1U satellite, in a case-study mission. The temperature patterns in the array are evaluated during the orbital period and the influence of operative temperature on the antenna responses and gain was considered. The thermal loads can affect the antenna matching, but, thanks to the optimized design, the proposed stacked antenna could operate from -100C to 100C, with analmost constant gain. Finally, folllowing a damage tolerant approach, the level of mechanical deformation which could be inducedon the communication system was studied. The analysis of stresses reveals that the stacked geometry could effectively be used in a space mission