All NASA exploration systems operate in the extreme environments of space and require reliable electronics capable of handling a wide temperature range (-180ºC to +130ºC) and high radiation levels. To design low-temperature radiation-hardened (rad-hard) electronics and predict circuit and system characteristics, such as error rates, modeling tools are required at multiple levels. To determine the electrical responses of transistors and circuits to radiation events, physics-based Technology Computer Aided Design (TCAD) and mixed-level tools are required. This project will provide models and tools that will improve capabilities for prediction of technology-dependent responses to radiation in wide temperature range, which will lead to better design of rad-hard electronics, better anticipation of design margins, and reduction of testing cost and time. Future NASA missions will use nanometer-scale electronic technologies which call for a shift in how radiation effects in such devices and circuits are viewed. Nano-scale electronic device responses are strongly related to the microstructure of the radiation event. This requires a more detailed physics-based modeling approach, which will provide information for higher-level engineering models used in integrated circuit (IC) and system design. Hence, the proposed innovation: detailed high-energy-physics-based simulations of radiation events (using MRED/Geant4 software from Vanderbilt University) efficiently integrated with advanced device/circuit response computations by CFDRC NanoTCAD three-dimensional (3D) mixed-level simulator. This will also enable a large number of statistically meaningful runs on a massively parallel supercomputing cluster. The extreme low temperature physics models combined with radiation effects will be validated with the help of consultant, Dr. John Cressler (Georgia Tech), in collaboration with the NASA Extreme Environment Electronics program, and serving the NASA RHESE Program (led by NASA-MSFC).