A generalized analysis is formulated that extends wind sail aerodynamics to a designer system engineering of solar sails through equivalent astrodynamics, astro-elasticity, astro- viscoelasticity, morphing and optimization. The analytical formulation is cast in terms of an inverse calculus of variations problem that leads to solutions yielding optimum solar sail material properties, sizing and geometries subject to preselected constraints, such as maximum thrust, high strength, minimum weight, stability and control, etc.