Recently, the ballistic missile interception system has gained significant attention as a major means of defense because of national and international defense-related concerns. An interceptor missile consists of a booster and a kill vehicle (KV). When designing an interceptor missile, it is crucial to understand the roles of the booster and KV to achieve balanced performance. In this paper, an optimization problem for designing the configuration of an interceptor missile is formulated by integrating the booster and KV. Unlike previous studies that considered the KV as a fixed parameter, we include the KV as a design variable. The optimization problem is formulated using the multidisciplinary design and optimization (MDO) methodology, and the performance metrics, design variables, and constraints are defined. Design variables are selected from parameters related to the configuration and performance of the booster and KV to achieve a balanced overall configuration. Several performance metrics related to intercepting probability are compared, and the launch weight, arrival time to target, and KV maneuverability are chosen as the main performance metrics.