Designing composite space capsules requires balancing structural, aerodynamic, and mission requirements, as improving one performance metric often compromises others. Thus, multi-objective optimization is essential for identifying design trade-offs. This study investigates three constrained three-objective optimization problems for a composite space capsule with carbon–epoxy and glass–epoxy shells. The objectives are: (1) minimizing total mass while maximizing internal volume and static stability margin; (2) maximizing natural frequency, buckling safety factor, and volumetric efficiency; and (3) minimizing structural deformation and ballistic coefficient while maximizing internal volume. We conducted optimization using a single-level multidisciplinary design optimization framework and a genetic algorithm. We analyzed solutions using three-dimensional Pareto fronts and parallel coordinate plots. Results reveal trade-offs among objectives in all three problems. Pareto-front comparisons show that, across most of the design space, the carbon–epoxy capsule has lower mass, greater stiffness, a higher buckling safety factor, and a higher natural frequency than the glass–epoxy variant, while maintaining comparable aerodynamic performance and meeting mission requirements.