Trade study reports should be maintained as part of

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Unformatted text preview: ove the measures and measurement methods (e.g., models) used in evaluating the alternatives, and then to repeat the analytical portion of the trade study process. 5.1.1 Controlling the Trade Study Process There are a number of mechanisms for controlling the trade study process. The most important one is the Systems Engineering Management Plan (SEMP). The SEMP specifies the major trade studies that are to be performed during each phase of the project life cycle. It An Example of a Trade Tree for a Mars Rover The figure below shows part of a trade tree for a robotic Mars rover system, whose goal is to find a suitable manned landing site. Each layer represents some aspect of the system that needs to be treated in a trade study to determine the best alternative. Some alternatives have been eliminated a priori because of technical feasibility, launch vehicle constraints, etc. The total number of alternatives is given by the number of end points of the tree. Even with just a few layers, the number of alternatives can increase quickly. (This tree has already been pruned to eliminate low-autonomy, large rovers.) As the systems engineering process proceeds, branches of the tree with unfavorable trade study outcomes are discarded. The remaining branches are further developed by identifying more detailed trade studies that need to be made. A whole family of (implicit) alternatives can be represented in a trade tree by a continuous variable. In this example, rover speed or range might be so represented. By treating a variable this way, mathematical optimization techniques can be applied. Note that a trade tree is, in essence, a decision tree without chance nodes. (See the sidebar on decision trees.) NASA Systems Engineering Handbook System Analysis and Modeling Issues Trade Study Reports Trade study reports should be prepared for each trade study. At a minimum, each trade study report should identify: • • • • • • • • The system issue under analysis System goals and objectives (or requirements, as appropriate to the leve...
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