A number of statistical cers have been developed to

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Unformatted text preview: mplexity of integrating life-cycle cost considerations into the design and development process should not be underestimated, but neither should the benefits, which can be measured in terms of greater cost-effectiveness. The existence of a rich set of potential life-cycle cost trades makes this complexity even greater. The Space Station Alpha Program provides many examples of such potential trades. As one example, consider the life-cycle cost effect of increasing the mean time between failures (MTBF) of Alpha's Orbital Replacement Units (ORUs). This is likely to increase the acquisition cost, and may increase the mass of the station. However, annual maintenance hours and the weight of annual replacement spares will decline. The same station availability may be achieved with fewer on-orbit spares, thus saving precious internal volume used for spares storage. For ORUs external to the station, the amount of extravehicular activity, with its associated logistics support, will also decline. With such complex interactions, it is difficult to know what the optimum point is. At a minimum, the system engineer must have the capability to assess the life-cycle cost of each alternative. (See Appendix B.8 on the operations and operations cost effects of ORU MTBF and Section 6.5 on Integrated Logistics Support.) 5.2.3 Cost Estimating The techniques used to estimate each life-cycle cost component usually change as the project life cycle proceeds. Methods and tools used to support budget estimates and life-cycle cost trades in Phase A may not be sufficiently detailed to support those activities during Phase C/D. Further, as the project life cycle proceeds, the requirements and the system design mature as well, revealing greater detail in the Work Breakdown Structure (WBS). This should enable the application of cost estimating techniques at a greater resolution. Three techniques are described below -parametric cost models, analogy, and grass-roots. Typically, the choice of technique depends on the state of information available...
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