For those issues for which the process of successive

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Unformatted text preview: trade studies are archived for future use. An essential feature of the systems engineering process is that trade studies are performed before decisions are made. They can then be baselined with much more confidence. At this point in the systems engineering process, there is a logical branch point. For those issues for which the process of successive refinement has proceeded far Simple Interfaces are Preferred According to Morris, NASA's former Acting Administrator George Low, in a 1971 paper titled "What Made Apollo a Success," noted that only 100 wires were needed to link the Apollo spacecraft to the Saturn launch vehicle. He emphasized the point that a single person could fully understand the interface and cope with all the effects of a change on either side of the interface. Figure 4—A Quantitative Objective Function, De" pendent on Life-Cycle Cost and All Aspects of Effectiveness. enough, the next step is to implement the decisions at that level of resolution (that is, unwind the recursive process). For those issues that are still insufficiently resolved, the next step is to refine the development further. Increase the Resolution of the Design. One of the first issues to be addressed is how the system should be subdivided into subsystems. (Once that has been done, the focus changes and the subsystems become systems -- from the point of view of a system engineer. The partitioning process stops when the subsystems are simple enough to be managed holistically.) As noted by Morris, "the divi- NASA Systems Engineering Handbook Fundamentals of Systems Engineering be managed holistically.) As noted by Morris, "the division of program activities to minimize the number and complexity of interfaces has a strong influence on the overal1 program cost and the ability of the program to meet schedules." Charles Leising and Arnold Ruskin have (separately) pointed out that partitioning is more art than science, but that there are guidelines available: To make interfaces clean and simple, sim...
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