The ability to perform these studies is enhanced by

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Unformatted text preview: ngerous to write them into the system specifications, as they can have just the opposite effect. Do Trade Studies. Trade studies begin with an assessment of how well each of the design alternatives meets the system goals (effectiveness, cost, schedule, and risk, both quantified and otherwise). The ability to perform these studies is enhanced by the development of system models that relate the design parameters to those assessments— but it does not depend upon them. Controlled modification and development of design concepts, together with such system models, often permits the use of formal optimization techniques to find regions of the design space that warrant further investigation— those that are closer to the optimum surface indicated in Figure 1. Whether system models are used or not, the design concepts are developed, modified, reassessed, and compared against competing alternatives in a closed-loop process that seeks the best choices for further development. System and subsystem sizes are often determined during the trade studies. The end result is the determination of NASA Systems Engineering Handbook Fundamentals of Systems Engineering bounds on the relative cost-effectivenesses of the design alternatives, measured in terms of the quantified system goals. (Only bounds, rather than final values, are possible because determination of the final details of the design is intentionally deferred. The bounds, in turn, may be derived from the probability density functions.) Increasing detail associated with the continually improving resolution reduces the spread between upper and lower bounds as the process proceeds. Select Concept. Selection among the alternative design concepts is a task for the system manager, who must take into account the subjective factors that the system engineer was unable to quantify, in addition to the estimates of how well the alternatives meet the quantified goals (and any effectiveness, cost, schedule, risk, or other constraints). When it is possible, it is usually well wor...
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