Lightweight stiffened shells, such as lattice, sandwich, and skin-stringer structures, are widely employed in rocket design owing to their high buckling strength. Although weight minimization under buckling constraints has been extensively studied for each structural type, selecting the most efficient configuration among them remains a key design issue. This study performs a comparative optimization of various stiffened shell types to identify the lightest configuration satisfying the prescribed buckling requirement and to elucidate their structural characteristics. The buckling load, used as a constraint, is evaluated through the finite element method (FEM) to ensure both accuracy and computational efficiency. To further reduce the analysis cost, a surrogate model is constructed to approximate the buckling load based on sampled design variables and FEM results. The model is iteratively refined using the Expected Feasibility (EF) function as an infill criterion to enhance prediction accuracy. The discrepancy between the FEM-calculated and surrogate-predicted buckling loads at the optimal solution was kept below 1%, confirming the reliability of the proposed approach. Among the examined structures, the sandwich configuration exhibited the lowest structural weight.
