The ultimate goal of human space exploration is to discover if life exists on other worlds, to understand the genesis and evolution of the universe and to learn to live on other planets. Mars offers the closest opportunity to pursue these goals realistically. The capabilities to define, design, develop, build, test, contract out, manufacture and operate new technologies are the means to achieve this set of goals. The purpose of this set of criteria is to evaluate mission design and exploration technology proposals to ensure that the means support the goals and do no obstruct them.This paper presents a comprehensive approach to evaluating complete Mars mission designs and partial designs. It begins from current theory and methodology of design problem definition. It proposes a method of evaluating if the mission design solution answers the problem definition. A process diagram encapsulates this process as passing through two evaluation gateways: Is the problem sufficiently well-defined to allow solution seeking? And, is the solution sufficiently well -defined to begin manufacturing?From this foundation, the paper proceeds to examine a series of cross-cutting issues that affect mission design reasoning, including the mass to orbit fallacy and the comparison of exploration modes. Technical credibility is a key to mission success, consisting of completeness, consistency, new technology development, temporal design logic and cost-effectiveness. System integration places particular demands upon the design logic, leading to performance measure for every significant aspect of the design and the technology. Operational practicality is another key parameter, encompassing the ever-present cost-effectiveness issue, plus protecting human health and safety, human productivity, sustainable operational capabilities, growth path to completion and a clear stopping point. All these factors contribute to establishing meaningful life cycle cost analyses, and the understanding of how to obtain the best value for the expenditure. The paper concludes with an appraisal of participatory design process as a means to integrate the stakeholders in a complex mission, and how the program management should approach handling all these factors.