this step begins the analytical portion of the trade

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Unformatted text preview: y process in simplest terms, beginning with the step of defining the system's NASA Systems Engineering Handbook Systems Analysis and Modeling Issues goals and objectives, and identifying the constraints it must meet. In the early phases of the project life cycle, the goals, objectives, and constraints are usually stated in general operational terms. In later phases of the project life cycle, when the architecture and, perhaps, some aspects of the design have already been decided, the goals and objectives may be stated as performance requirements that a segment or subsystem must meet. At each level of system resolution, the system engineer needs to understand the full implications of the goals, objectives, and constraints in order to formulate an appropriate system solution. This step is accomplished by performing a functional analysis. Functional analysis is the systematic process of identifying, describing, and relating the functions a system must perform in order to fulfil1 its goals and objectives. In the early phases of the project life cycle, the functional analysis deals with the top-level functions that need to be performed by the system, where they need to be performed, how often, under what operational concept and environmental conditions, and so on. The functional analysis needs only to proceed to a level of decomposition that enables the trade study to define the system architecture. In later phases of the project life cycle, the functional analysis proceeds to whatever level of decomposition is needed to fully define the system design and interfaces. (See sidebar on functional analysis techniques.) Closely related to defining the goals and objectives, and performing a functional analysis, is the step of defining the measures and measurement methods for system effectiveness (when this is practical), system performance or technical attributes, and system cost. (These variables are collectively called outcome variables, in keeping with the discussion in Section 2.3. Some systems engineering books refer to these variables as decision criteria, but this term should not be confused with selection rule, described below. Sections 5.2 and 5.3 discuss the concepts of system cost and system effectiveness, respectively, in greater detail.) This step begins the analytical portion of the trade study process, since it suggests the...
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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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