A second and major problem is that an expression or

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Unformatted text preview: outside, independent corroboration. Responsiveness of a model is a measure of its power to distinguish among the different alternatives being considered in a trade study. A responsive lunar base cost model, for example, should be able to distinguish the costs associated with different system architectures or designs, operations concepts, or logistics strategies. Another desirable model characteristic is transparency, which occurs when the model's mathematical relationships, algorithms, parameters, supporting data, and inner workings are open to the user. The benefit of this visibility is in the traceability of the model's results. Not everyone may agree with the results, but at least they know how they were derived. Transparency also aids in the acceptance process. It is easier for a model to be accepted when its documentation is complete and open for comment. Proprietary models often suffer from a lack of acceptance because of a lack of transparency. Upfront user friendliness is related to the ease with which the system engineer can learn to use the model and prepare the inputs to it. Backend user friendliness is related to the effort needed to interpret the model's results and to prepare trade study reports for the tentative selection using the selection rule. 5.1.3 Selecting the Selection Rule The analytical portion of the trade study process serves to produce specific information on system effectiveness, its underlying performance or technical attributes, and cost (along with uncertainty ranges) for a few alternative system architectures (and later, system designs). These data need to be brought together so that one alternative may be selected. This step is accomplished by applying the selection rule to the data so that the alternatives may be ranked in order of preference. The structure and complexity of real world decisions in systems engineering often make this ranking a difficult task. For one, securing higher effectiveness almost always means incurring higher costs and/or facing greater uncertainties. In order to choose among alternatives with different levels of effectiveness and costs, the system engineer must understand how much of one is worth in terms of...
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