NASA-Systems Engineering

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Unformatted text preview: Once it is understood what the system is to accomplish, it is possible to devise a variety of ways that those goals can be met. Sometimes, that comes about as a consequence of considering alternative functional allocations and integrating available subsystem design options. Ideally, as wide a range of plausible alternatives as is consistent with the design organization's charter should be defined, keeping in mind the current stage in the process of successive refinement. When the bottom-up process is operating, a problem for the system engineer is that the designers tend to become fond of the designs they create, so they lose their objectivity; the system engineer often must stay an "outsider" so that there is more objectivity. On the first turn of the spiral in Figure 3, the subject is often general approaches or strategies, sometimes architectural concepts. On the next, it is likely to be functional design, then detailed design, and so on. The reason for avoiding a premature focus on a single design is to permit discovery of the truly best design. Part of the system engineer's job is to ensure that the design concepts to be compared take into account all interface requirements. "Did you include the cabling?" is a characteristic question. When possible, each design concept should be described in terms of controllable design parameters so that each represents as wide a class of designs as is reasonable. In doing so, the system engineer should keep in mind that the potentials for change may include organizational structure, schedules, procedures, and any of the other things that make up a system. When possible, constraints should also be described by parameters. Owen Morris, former Manager of the Apollo Spacecraft Program and Manager of Space Shuttle Systems and Engineering, has pointed out that it is often useful to define design reference missions which stress all of the system's capabilities to a significant extent and which al1 designs will have to be able to accomplish. The purpose of such missions is to keep the design space open. Consequently, it can be very da...
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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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