chart provided as Figure E.1 diagrams the end-to-end effort as described by these principles and executed for this report.

•   Use multiple methods and databases regarding past space systems so that no one model or database biases the results.

•   Use analogy-based estimating that anchors cost and schedule estimates to NASA systems that have already been built with a known cost and schedule.

•   Use system-level estimates as well as a build-up to system-level estimates by appropriately summing subsystem data so as not to underestimate system cost and complexity.

•   Use cross-checking tools, such as Complexity Based Risk Assessment (CoBRA), to cross-check cost and schedule estimates for internal consistency and risk assessment.

•   In an integrated fashion, quantify the total threats to costs from schedule growth, the costs of maturing technology, and the threat to costs owing to mass growth resulting in the need for a larger, more costly launch vehicle.

The general CATE methodology for cost assessment is presented in Figure E.2. As with most cost assessment approaches, the CATE process uses mission analogies, growth metrics, and other relevant criteria applied to each work breakdown structure element that are derived from measured cost and schedule performance on past NASA (and selected Department of Defense) missions. Probabilistic methods are then employed using a triangle distribution to calculate the reserves needed to move the sum of the most

image

FIGURE E.1 Flow chart for the CATE process. SOURCE: Provided by the Aerospace Corporation under contract with the National Research Council.

 



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