This paper presents a load control algorithm for control of energy sources and loads to enhance energy sustainability and reliability of the International Space Station (ISS), which is a large spacecraft in orbit around Earth. In this paper, the ISS electric power system was simulated in MATLAB/Simulink to be able to evaluate the performance of the developed algorithm in a simulated environment. This study also aims to emphasize the importance of load control algorithms on energy sustainability for critical systems, like ISS, having limited energy sources.