Improvements to solar cell efficiency that is consistent with low cost, high volume fabrication techniques are critical for future NASA space missions. In this project, we propose a novel, ultra-thin (UT), Si photovoltaic cell technology that combines enhanced light trapping (LT) and absorption due to nanostructured surfaces, separation of photogenerated carriers by carrier selective contacts (CSC), and increased carrier density due to multiple exciton generation (MEG). Such solar cells have a potential to achieve the efficiencies of 40+%, while being rad-hard, lightweight, flexible, and lowcost, due to use of Si high volume techniques. CFDRC will partner with the QESST ERC center at Arizona State University (ASU) to develop and demonstrate a novel, ultra-thin, nanostructured Si photovoltaic cell technology. Phase I project will include modeling and experimental design, for a UT flexible Si based solar cell, that can achieve >25% AM0 conversion efficiency. Additionally, several approaches will be investigated to improve Si solar cell radiation hardness/tolerance. In Phase II, the physical mechanisms currently limiting light trapping, open-circuit voltage (Voc), and MEG will be identified, and addressed. The UT rad-hard cell design will be optimized (for > 36% efficiency) and a solar cell will be fabricated and presented for testing.