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Later in phase b the effort shifts to establishing a

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Unformatted text preview: e NAR also seeks to evaluate the cost and schedule estimates, and the contingency reserve in these estimates. The timing of this review is often driven by the Federal budget cycle, which requires at least 16 months between NASA's budget preparation for submission to the President's Office of Management and Budget, and the Congressional funding for a new project start. (See Section 3.8.) There is thus a natural tension between the desire to have maturity in the project at the time of the NAR and the desire to progress efficiently to final design and development. Later in Phase B, the effort shifts to establishing a functionally complete design solution (i.e., a "design-to" baseline) that meets mission goals and objectives. Trade studies continue. Interfaces among the major end items are defined. Engineering test items may be developed and used to derive data for further design work, and project risks are reduced by successful technology developments and demonstrations. Phase B culminates in a series of preliminary design reviews (PDRs), containing the system-level PDR and PDRs for lower-level end items as appropriate. The PDRs reflect the successive refinement of requirements into designs. Design issues uncovered in the PDRs should be resolved so that final design can begin with unambiguous "design-to" specifications. From this point on, almost all changes to the baseline are expected to represent successive refinements, not fundamental changes. Prior to baselining, the system architecture, preliminary design, and operations concept must have been validated by enough technical analysis and design work to establish a credible, feasible design at a lower level of detail than was sufficient for Phase A. 3.4 Phase C—Design The purpose of this phase is to establish a complete design (“build-to" baseline) that is ready to fabricate (or code), integrate, and verify. Trade studies continue. Engineering test units more closely resembling actual hardware are built and tested so as to establish confidence that the design will function in the expected environments. Engineering specialty analysis results are inte...
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