NASA-Systems Engineering

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Unformatted text preview: th the trouble to develop a mathematical expression, called an objective function, that expresses the values of combinations of possible outcomes as a single measure of cost-effectiveness, as is illustrated in Figure 4, even if both cost and effectiveness must be described by more than one measure. When achievement of the goals can be quantitatively expressed by such an objective function, designs can be compared in terms of their value. Risks associated with design concepts can cause these evaluations to be somewhat nebulous (because they are uncertain and are best described by probability distributions). In this illustration, the risks are relatively high for design concept A. There is little risk in either effectiveness or cost for concept B. while the risk of an expensive failure is high for concept C, as is shown by the cloud of probability near the x axis with a high cost and essentially no effectiveness. Schedule factors may affect the effectiveness values, the cost values, and the risk distributions. The mission success criteria for systems differ significantly. In some cases, effectiveness goals may be much more important than all others. Other projects may demand low costs, have an immutable schedule, or require minimization of some kinds of risks. Rarely (if ever) is it possible to produce a combined quantitative measure that relates all of the important factors, even if it is expressed as a vector with several components. Even when that can be done, it is essential that the underlying factors and relationships be thoroughly revealed to and understood by the system manager. The system manager must weigh the importance of the unquantifiable factors along with the quantitative data provided by the system engineer. Technical reviews of the data and analyses are an important part of the decision support packages prepared for the system manager. The decisions that are made are generally entered into the configuration management system as changes to (or elaborations of) the system baseline. The supporting...
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This document was uploaded on 02/26/2014 for the course E 515 at University of Louisiana at Lafayette.

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