Solar Arrays for LILT and High-Radiation Environments

We propose an ultra-high efficiency lightweight scalable solar array technology that meets all the goals set by the Appendix. This technology relies on solar cells having an advanced device architecture with proven high-efficiency capability, and featuring a modified design that enables optimal performance in low irradiance, low temperature and high-radiation (LILT/Rad) environments. In combination with lightweight blanket-array technology, these cells significantly advance the array performance in extreme environments, offering six times higher specific power and packaging density than the current state-of-art (SoA). Our strategy stems from recognizing that cell efficiency is the single most leveraging parameter on the overall array performance. We are therefore making LILT/Rad cell efficiency advancement the top priority for the development effort. The proposed cell is based on SolAero's IMM4 (inverted metamorphic 4-junction) product, which currently holds the efficiency record at 1AU. The current IMM4 design, which is optimized for Earth orbit, is expected to suffer from performance degradation under LILT/Rad conditions. The project will investigate, identify, and eliminate from the design the root causes for any such degradation mechanisms. The resulting new, modified cell design will have optimal efficiency at LILT/Rad. The modified IMM4 is predicted to meet the Appendix cell-efficiency goals with significant margin, in both flat-plate and concentrator systems. This cell technology will deliver 20% higher LILT/Rad efficiency and 30% lower mass at the CIC (coverglassed interconnected cell) level than the SoA. At the system level, the proposed array is a flat-plate concept as the baseline, with a concentrator concept also being considered as a backup. In principle concentrators promise a boost in power efficiency over flat-plate. However, real-world space concentrators have so far failed to deliver on that promise, as they suffer from a variety of shortcomings and risks, mainly due to increased system complexity. During the Base phase, a trade study will decide between the flat-plate and the concentrator system solutions. This study will include a risk assessment, informed by the early results of the cell development task. Following the system concept down-select, a competitive procurement process will choose an array partner, who will join the project for the Option I and Option II phases. For meeting the array-level specific power performance goal, we expect that little or no development will be necessary on the baseline array structure. Flat-plate scalable blanket-array technologies such as ATK MegaFlex and DSS MegaRosa have already been developed by NASA for solar-electric propulsion applications. In combination with LILT/Rad-optimized cells, such arrays are estimated to deliver 9W/kg of specific power at LILT end of life. Similarly, we expect that the packaging density, stowed launch, and high-voltage/plasma goals will be met by heritage 1AU array designs without need for modification beyond the cell level; these assumptions will be verified through test and analysis. Cell development will occur during the Base and Option I phases; during Option II, cell work will focus on qualification, manufacturability and integration. At the array level, a coupon representative of the proposed technology will be built and tested during Option I. Then, a scalable prototype panel representative of the array technology will be built and its performance will be validated during Option II. The proposed solar arrays are an enabling technology for solar electric propulsion to Jupiter and beyond. They are also enabling for the solar-powered exploration of deep-space targets at >10AU that would otherwise only be accessible with nuclear power sources. And, for missions traveling to 2-10AU destinations, this technology is strongly enhancing, offering significantly improved power capabilities over the SoA. More »