The Interstage structure of an H-2A launch vehicle was developed as CFRP and foam core sandwich structure by co-curing technique. In the design analysis, nonlinear buckling analysis for a sandwich panel
cylinder was conducted considering the imperfection effect of the actual cylinder shape. The manufacturing process of the co-cured composite cylinder was established in various manufacturing tests. The
Interstage structure was qualified by a full-scale strength test. The required cost and weight target was achieved.