Sound design of complex, interactive, safety critical systems is very important, yet difficult. A particular challenge in the design of safety-critical systems is a typical lack of access to large numbers of testers and an inability to test early designs with traditional usability assessment tools. This inability leads to reduced information available to guide design, a phenomenon referred to as the Collingridge dilemma. Our research proposes to address parts of this problem with the development of tools and techniques for generating useful information and assessing developing designs early, to minimize the need for late change. More generally, we describe a set of three tools and techniques to support the process of ensuring fitness-for-purpose of complex interactive systems, helping designers focus on interaction across different functions of an overall system. These different tools and techniques support different parts of the overall design and evaluation process, but are focused on improving the coverage and effectiveness of evaluating interaction.