A unique ultra-light solar concentrator has recently been developed for space power applications. The concentrator comprises a flexible, 140-micron-thick, line-focus Fresnel lens, made in a continuous process from space-qualified transparent silicone rubber material. For deployment and support in space, end arches are used to tension the lens material in a lengthwise fashion, forming a cylindrical stressed membrane structure. The resultant lens provides high optical efficiency, outstanding tolerance for real-world errors and aberrations, and excellent focusing performance. The stretched lens is used to collect and focus sunlight at 8X concentration onto high-efficiency multi-junction photovoltaic cells, which directly convert the incident solar energy to electricity. The Stretched Lens Array (<i>SLA</i>) has been measured at over 27% net solar-to-electric conversion efficiency for space sunlight, and over 30% net solar-to-electric conversion efficiency for terrestrial sunlight. More importantly, the SLA provides over 180 W/kg specific power at a greatly reduced cost compared to conventional planar photovoltaic arrays in space. The cost savings are due to the use of 85% less of the expensive solar cell material per unit of power produced. SLA is a direct descendent of the award-winning <i>SCARLET</i> array which performed flawlessly on the NASA/JPL Deep Space 1 spacecraft from 1998-2001.
Silicone lens materials, baselined for space power applications, were exposed to various components of a Geosynchronous Earth Orbit (GEO) radiation environment to determine the suitability of the material for long-term missions. Sample materials were exposed to electrons, protons, Near Ultraviolet (NUV), and Vacuum Ultraviolet (VUV) radiation. The samples were exposed to individual and to various combinations of these space environmental components. The electron and proton exposure levels were determined from radiation measurements performed in GEO. NUV and VUV radiation exposures were based on solar emissions at zero air mass (AM0). Lens material degradation was determined by the change in optical spectral transmission of the silicone materials. A reduction in the transmittance of the material will reduce the power generating potential of solar cells. The spectral transmission was measured at Marshall Space Flight Center (MSFC), after exposure to space environmental elements including electrons, protons, VUV and NUV. Entech, Inc. conducted performance tests on samples exposed to short duration proton and electron radiation. Results of these tests will be discussed. Minor degradation was witnessed on samples exposed to NUV and VUV light. The largest transmission spectral degradation occurred in the wavelength range below the quantum efficiency of space qualified solar cells. Transmission degradation in the wavelength range of maximum solar cell quantum efficiency was small.