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Running an alternative through an operational time

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Unformatted text preview: urther consideration in trade studies those alternatives that cannot meet the system's goals and objectives To provide insights to the system-level (and below) model builders, whose mathematical models will be used in trade studies to evaluate the alternatives. Several techniques are available to do functional analysis. The primary functional analysis technique is the Functional Flow Block Diagram (FFBD). These diagrams show the network of actions that lead to the fulfillment of a function. Although the FFBD network shows the logical sequence of “what" must happen, it does not ascribe a time duration to functions or between functions. To understand timecritical requirements, a Time Line Analysis (TLA) is used. A TLA can be applied to such diverse operational functions as spacecraft command sequencing and launch vehicle processing. A third 2 technique is the N diagram, which is a matrix display of functional interactions, or data flows, at a particular hierarchical level. Appendix B.7 provides further discussion and examples of each of these techniques. NASA Systems Engineering Handbook Systems Analysis and Modeling Issues costs less than x dollars (with some given probability), meets safety requirements, and possibly meets other political or schedule constraints. Defining the selection rule is essentially deciding how the selection is to be made. This step is independent from the actual measurement of system effectiveness, system performance or technical attributes, and system cost. Many different selection rules are possible. The selection rule in a particular trade study may depend on the context in which the trade study is being conducted—in particular, what level of system design resolution is being addressed. At each level of the system design, the selection rule generally should be chosen only after some guidance from the next higher level. The selection rule for trade studies at lower levels of the system design should be in consonance with the higher level selection rule. Defining plausi...
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