Optical coating technology developed for advanced flexible solar space power applications

Thin film optical coatings plays a prominent role in the development of efficient, light weight, flexible solar power arrays for future space applications. Initially, the Boeing High Technology Center (circa 1990) explored various ways of protecting ENTECH\´s DC93-500 silicone Fresnel lenses from the intense UV radiation of the space environment. Boeing\´s prototype design used mini-dome lenses to focus solar energy onto small dual-junction high-efficiency solar cells to generate electrical power. To protect the silicone lenses from solar UV darkening, one early approach involved using a cerium-doped glass cover cemented over the lens. Unfortunately, during launch simulation shock testing the glass lens covers cracked. We then explored the concept of depositing a UV blocking thin film coating directly onto the silicone lens surface. This provided a challenge of immense proportions analogous to pouring a thin layer of concrete onto the surface of a reservoir filled with "Jell-O." Differential between the coefficient of thermal expansion of the DC93-500 silicone and the deposited dielectric optical coating had to be balanced with intrinsic stress of the optical coating materials. This work culminated, some fifteen years later, in the coating technology developed for the Stretched Lens Array Square Rigger (SLASR). SLASR was designed to replace classic flat panel solar arrays with a lighter, lower cost, and more efficient (30%) concentrator arrays for future space applications. Currently, there are several space power development programs that rely on the use of polymeric materials to protect and provide flexibility to the solar array. Even though this coating technology was first developed for concentrators, it is now being successfully applied to a new class of polymers, providing UV protection while maintaining optical performance after deformation due to flexing.