pearing later in the queue have some assurance that the mission will indeed be implemented and remain an integral part of Earth system science. Retention of and investment in such long-term priorities are thus crucial to enabling a balanced program and reaffirming NASA’s commitment to the entire suite of missions. To maintain the survey’s long-term vision for a balanced Earth system science and applications program, this fixed and predictable queue would be complemented by a steady stream of opportunities to facilitate the demonstration of innovative ideas and higher-risk technologies to provide a mechanism to support new discoveries and add an element of flexibility to the program.
The science priorities identified by the 2007 decadal survey have provided the foundation for advancing Earth system science with the recommended set of missions. In its assessment of NASA’s implementation of the survey, the committee discussed at length whether specific mission recommendations were a necessary part of science priority setting, and presenters to the committee over the course of the study did not always favor one approach over the other. Finding balance between prioritizing science objectives and constraining how those objectives are accomplished will no doubt be one of the major tasks for any future study aimed at creating a new mission queue and set of scientific objectives for NASA’s Earth science program. However, the committee concluded that establishing at least notional mission concepts that can accomplish the prioritized objectives is essential to ensuring that the priorities are indeed reasonable and achievable. Similarly, development of mission recommendations allows for a sense of scope and scale to be conveyed that is lacking from a simple listing of target areas for investment. The committee thought that establishing science priorities devoid of implementation recommendations could easily be misconstrued as endorsements for one discipline over another.
In the course of this midterm assessment of the 2007 decadal survey’s implementation, it became apparent to the committee that large cost growth in missions early in the queue presents a real danger to programmatic balance. It also tends to encourage commensurate growth in later missions, effectively stretching program implementation and pushing later missions inexorably toward future dates, thus discouraging entire segments of the Earth science community and threatening the Earth system science goals set forth by the survey.
However, future community prioritization exercises should avoid pursuing the path of ever-more-detailed cost estimates at the expense of attention to scientific priority setting—the latter being the primary goal of any such review. Even in a cost-constrained environment, some mission cost growth is likely, if not inevitable. The committee does not discourage rigorous cost estimation at the appropriate time during formulation, a practice that serves an important purpose—but equally important is setting up clear budgetary decision rules that will help decision makers adjust to a changing fiscal environment and maintain the overall goals laid out in the vision put forth in any suggested future program.2 To supplement such budgetary decision rules, consideration should be given to the use of mission cost caps that would help prevent
2 Consideration should be given to establishing relative investment levels for recommended missions rather than leaving the cost of recommended missions unconstrained. Individual missions, then, would not claim enduring priority over other missions regardless of ultimate implementation cost, thus facilitating maintenance of programmatic balance across Earth system science. NASA would set an appropriate cost cap once more detailed implementation studies, guided by the recommended investment level, have been completed. The 2007 decadal survey attempted to convey a sense of scale through its rough cost estimates, but it stopped short of establishing or recommending a cost cap approach.