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Design capability indices provide a metric to assess the capability of a family of designs, represented by a range of top-level design specifications, to satisfy a ranged set of design requirements. Design capability indices can be used to manage design freedom in the early stages of the design process when design requirements for a system may be uncertain. To illustrate the use of design capability indices, the design of a family of General Aviation aircraft is presented: design capability indices are used to simultaneously design a family of three aircraft around a two, a four, and a six seater configuration. The results are compared against two of our previous studies.

We believe that the efficiency and effectiveness of human designers can be improved by making available tools that can be used to help negotiate solutions to open or unstructured parts of the process of designing. We assert that the efficiency and effectiveness of a designer can be increased by increasing the speed with which the design iteration is accomplished and reducing of the number of iterations. An increment in the iteration speed can be achieved if at least some parts of a design process are known and can be modelled on a computer. One way of reducing the number of iterations in design is by avoiding this corrective redesign. This provides the stimulus for developing approaches to design that include Concurrent Engineering considerations. Thus, in our opinion, a necessary ingredient in increasing efficiency and effectiveness of human designers is the modeling of design processes in a manner that they can be analyzed, manipulated and implemented.

A computer-based design system has been developed for conceptual design of spacecraft active thermal control systems (ATCS). Its purpose is to aid the thermal systems engineer in selection of a working fluid and thermal cycle for a given set of requirements. It allows the user to specify the desired relative importance of several criteria, including system mass, pumping power, and fluid toxicity. The design problem is formulated as a coupled selection-compromise Decision Support Problem, and solved concurrently using DSIDES, a design software package developed at the University of Houston. By using this system, a designer is able to analyze both vapor compression and pumped two-phase thermal cycles, and up to four working fluids simultaneously. A case study based on Space Station Freedom thermal control requirements has been implemented. The fluids considered are Water, R-11, R-114, and Ammonia.