Advanced optical coating technology used in the development of concentrator arrays for solar space power applications

Since 1990 thin film optical coatings have taken a prominent role in the development of highly efficient solar power concentrators for future space applications. During the initial development of this coating technology, the Boeing High Technology Center explored various ways of protecting ENTECH's DC93-500 silicone Fresnel lenses from the harsh space environment. ENTECH's mini-dome lenses focused solar energy onto small high-efficiency solar cells for generating electrical power. To protect the silicone lenses from solar UV darkening, one early approach involved a cerium-doped glass cover cemented over the lens. Unfortunately, during launch simulation shock testing the glass lens covers cracked. We next explored the deposition of a UV blocking thin film coating directly to the silicone lens surface. This was a problem of immense proportions analogous to pouring concrete on to the surface of a reservoir filled with "Jell-O." Differential in coefficient of thermal expansion between the DC93-500 silicone and the deposited dielectric optical coating had to be balanced with intrinsic stress of the optical coating materials. Ion Beam Optics' work has culminated, some fifteen years later, in the current coating technology that is being incorporated in the Stretched Lens Array SquareRigger (SLASR). SLASR is designed to replace classic flat panel solar arrays with a lighter, lower cost, and more efficient (30%) concentrator arrays for future space applications. This paper will describe the coating technology and show its performance and benefits for SLASR space power systems. Results from both ground tests and space flight tests will be presented.