We are developing CAD tools, models and methodologies for electronics design for circuit operation in extreme environments with a focus on very low temperature and radiation effects. These new tools will help enable NASA to design next generation electronics especially for planetary projects including the Europa Jupiter System Mission. The new models and tools will be directly incorporated into industry standard CAD products to ensure their usability and extend their applicability to extreme environments. Such capabilities will significantly improve reliability, performance and lifetime of electronics that are used for space missions. This will be achieved through the development of novel compact and distributed device modeling capabilities for radiation-hard and extreme temperature instrument design, as well as techniques for circuit design that help to predict the vulnerability of circuits to degradation and upset from radiation. Research and development is indicating that standard bulk silicon CMOS and SOI processes operate well under these extreme conditions so that there is little need for NASA to commit to large expenditures for exotic materials. Models and CAD tools are relatively inexpensive as compared to fabrication costs; thus the results of this project should provide a very large return on investment.