Many future space optical systems are dependent on large apertures to achieve the collecting power or resolution necessary to meet mission goals. Traditional mirror materials such as glasses and metals result in optics which are heavy and costly to both fabricate and deploy. In recent years, an approach for fabricating large, lightweight, precision optics from fiber reinforced organic matrix composite materials has been developed and demonstrated. These mirror panels consist of composite facesheets bonded to an open cell core. A key element of this technology is the durability of the composite construction materials. Extensive testing has been performed on a number of composite materials based on carbon fiber and organic resins. Ultimately, a high modulus graphite fiber/cyanate ester composite system was chosen for the panel facesheets due to its superior mechanical properties, processability, thermal stability, radiation resistance, very low water absorption, and temporal stability. This program has successfully demonstrated the feasibility of fabricating space durable mirrors using composite materials technology.