This study presents a comparison of competing space-based architectures given the progress made with high-energy lasers, large optics, and atmospheric compensation techniques within the past several years. Three space-based architectures are evaluated against the ballistic missile threat: space-based lasers, ground-based lasers in conjunction with orbiting mirrors, and a combined approach using space-based lasers with orbiting mirrors. The results of this study suggest that the most technically sound and cost efficient architecture is space-based lasers with orbiting mirrors.