Systems Engineering

Optimization and selection is done at all levels of engineering design. In the Systems Engineering process it is first applied at a high level to concepts before detailed design is performed. Optimization is varying parameters within a single concept or element in order to find the best values for those parameters. Trade Studies compare different concepts in order to select the best one. Different parameters like weight, cost, and risk cannot be directly compared. So they are scored by measures of effectiveness (see page 1). The concept or optimized parameters that yield the highest score is the "best option". In the early stages of design, there will be larger uncertainties in parameters like weight and performance. Finding how much effect variations in such parameters have is called Sensitivity Analysis. Knowing those will guide which areas to work on to reduce uncertainties.

If the difference in evaluation score between two concepts is sufficiently more than their uncertainties, the lower scoring one may safely be discarded. If the scores are within the range of uncertainties, both should be worked on in more detail until a clear winner emerges. If the effort to reduce uncertainty is judged more than the uncertainty reduction is worth, then one of the competing choices can be selected arbitrarily. Note that optimization of a system as a whole may not mean optimization of each individual part, since the parts can interact in a complex way. Once the optimization and selection is completed, the results are recorded and used to update the system concept and current design configuration.