The process of finding the most cost effective design

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Unformatted text preview: effectiveness for another at the same cost, the decisions become harder. Figure 2--Estimates of Outcomes to be Obtained from Several Design Concepts Including Uncertainty. The process of finding the most cost-effective design is further complicated by uncertainty, which is shown in Figure 2 as a modification of Figure 1. Exactly what outcomes will be realized by a particular system design cannot be known in advance with certainty, so the projected cost and effectiveness of a design are better described by a probability distribution than by a point. This distribution can be thought of as a cloud which is thickest at the most likely value and thinner farther away from the most likely point, as is shown for design concept A in the figure. Distributions resulting from designs which have little uncertainty are dense and highly compact, as is shown for concept B. Distributions associated with risky designs may have significant probabilities of producing highly undesirable outcomes, as is suggested by the presence of an additional low effectiveness/high cost cloud for concept C. (Of course, the envelope of such clouds cannot be a sharp line such as is shown in the figures, but must itself be rather fuzzy. The line can now be thought of as representing the envelope at some fixed confidence level -- that is, a probability of x of achieving that effectiveness.) Both effectiveness and cost may require several descriptors. Even the Echo balloons obtained scientific data on the electromagnetic environment and atmospheric drag, in addition to their primary mission as communications satellites. Furthermore, Echo was the first satellite visible to the naked eye, an unquantified -but not unrecognized —aspect of its effectiveness. Costs, the expenditure of limited resources, may be measured in the several dimensions of funding, personnel, use of facilities, and so on. Schedule may appear as an attribute of effectiveness or cost, or as a constraint. Sputnik, for example, drew much NASA Systems Engineering Handbook Fundamentals of Systems Engineering of its effe...
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