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Unformatted text preview: quot;wrapped" (multiplied by a factor greater than one) to cover the costs of integration and test, program management systems engineering, etc. These additional costs are NASA Systems Engineering Handbook Systems Analysis and Modeling Issues called system-level costs, and are often calculated as percentages of the direct costs. Using Parametric Cost Models. A number of parametric cost models are available for costing NASA systems. Some of these are shown in Table 5. Unfortunately, none alone is sufficient to estimate life-cycle cost. Assembling an estimate of life-cycle cost often requires that several different models (along with the other two techniques) be used together. To integrate the costs being estimated by these different models, the system engineer should ensure that the inputs to and assumptions of the models are consistent, that all relevant life-cycle cost components are covered, and that the timing of costs is correct. The system engineer may sometimes find it necessary to make some adjustments to model results to achieve Learning Curve Theory The learning curve (also known as the progress or experience curve) is the time-honored way of dealing with the empirical observation that the unit of fabricating multiple units of complex systems like aircraft and spacecraft tends to decline as the number increases. In its usual form, the theory states that as the total quantity produced doubles, the cost per unit decreases by a constant percentage. The cost per unit may be either the average cost over the number produced, or the cost of the last unit produced. In the first case, the curve is generally known as the cumulative average learning curve; in the second case, it is known as the unit learning curve. Both formulations have essentially the same rate of learning. Let C(1) be the unit cost of the first production unit, and C(Q) be the unit cost of the Qth production unit, then learning curve theory states there is a number, b, such that C(Q) = C(1) Qb The number b is specified by the rate of learning. A 90 percent learning rate means that the unit cost of t...
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