Abstract: The rapid development of commercial space activities and the accelerated deployment of mega-constellations have led to increasing congestion in the vast low-Earth orbit (LEO) regions. Research on orbital capacity in these regions is therefore of great theoretical significance and engineering value. This paper investigates the maximum feasible orbital capacity of low-orbit space as well as the optimization of high-density heterogeneous constellations. A method is proposed to calculate the theoretical upper bound of constellation feasible capacity. Based on this method, a heuristic framework is further developed to estimate the maximum feasible capacity of remaining satellites within the same orbital shell under existing constellation configurations, thereby providing a reference for the construction and optimization of large-scale LEO heterogeneous constellations.