Often during Product Development, externalities or requirements change, forcing design change. This uncertainty adversely affects program outcome, adding to development time and cost, production cost, and can compromise system performance. We present a development approach that minimizes impacts, by proactively considering the possibility of changes in the externalities and mid-course design changes. The approach considers the set of alternative designs and the burdens of a mid-course change from one design to another in determining the relative value of a specific design through the set-based design methodology. The approach considers and plans parallel (redundant) development of alternative designs with progressive selection of options, including time-versus-cost tradeoffs and the impact change-costs. The approach includes a framework of the development process addressing design and integration lead-times, their relationship to the time-order of design decisions, and the time-dependent burden of design changes. We also compare set-based and single point design schemes.