The systems engineering process can be thought of as

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Unformatted text preview: alternatives are precisely enough defined and thoroughly enough understood to be well differentiated in the cost-effectiveness space, then the system manager can make choices among them with confidence. The systems engineering process can be thought of as the pursuit of definition and understanding of design alternatives to support those decisions, coupled with the overseeing of their implementation. To obtain assessments that are crisp enough to facilitate good decisions, it is often necessary to delve more deeply into the space of possible designs than has yet been done, as is illustrated in Figure 3. It should be realized, however, that this spiral represents neither the project life cycle, which encompasses the NASA Systems Engineering Handbook Fundamentals of Systems Engineering system from inception through disposal, nor the product development process by which the system design is developed and implemented, which occurs in Phases C and D (see Chapter 3) of the project life cycle. Rather, as the intellectual process of systems engineering, it is inevitably reflected in both of them. Figure 3 is really a double helix—each create concepts step at the level of design engineering initiates a caAs an Example of the Process of Successive Refinement, Consider the Choice of Altitude for a Space Station such as Alpha • The first issue is selection of the general location. Alternatives include Earth orbit, one of the Earth-Moon Lagrange points, or a solar orbit. At the current state of technology, cost and risk considerations made selection of Earth orbit an easy choice for Alpha. • Having chosen Earth orbit, it is necessary to select an orbit region. Alternatives include low Earth orbit (LEO), high Earth orbit and geosynchronous orbit; orbital inclination and eccentricity must also be chosen. One of many criteria considered in choosing LEO for Alpha was the design complexity associated with passage through the Van Allen radiation belts. • System design choices proceed to the selection of an altitude maintenance strategy—rules that implicitly determine when, where, and why to reboost, such as "maintain altitud...
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