Abstract: Film-based composite structures meet the requirements of highly weight-efficient SDI space-based systems. These structures are rigid, lightweight, dimensionally stable, and possess a high degree of structural damping. Thin-walled structures (wall thickness less than 50 .mu.) made from self-reinforced ordered-polymer films overcome drawbacks of fiber-reinforced composites, and provide resistance to microcracking, ply delamination and impact. They have high temperature capability (over 300.degree. C.), low temperature (cryogenic) capability and the capability for hardening and survivability. The modulus and dimensional stability of film-based ultralightweight honeycomb sandwich structures is better than currently possible with aluminum or fiber-reinforced composite materials. Other thin-walled structures such as tension web beams and thin facesheets also show similar stiffness-to-weight advantages over current materials.