Vision and Voyages for Planetary Science in the - Solar System ...

thorough study of many objects, a balanced portfolio may contain a variety of mission categories,
depending on the level of investigation that has been conducted previously.
The workshop report mentioned above developed criteria by which a scientific program might be
assessed. Although written almost five years ago, the criteria, slightly rephrased, are still relevant:
• Capacity to make steady progress—Does the proposed program make reasonable progress
toward the scientific goals set forth in the decadal survey? Are the cadence of missions and the planning
process such that new scientific discoveries can be followed up rapidly with new missions, such as small
missions in the Discovery program? Does the program smoothly match and complement programs
initiated by prior decadal surveys?
• Stability—Can one construct an orderly sequence of missions, meeting overarching scientific
goals, developing advanced technology, sizing and nurturing the research and technical community and
providing for appropriate interactions with the international community? Is the program stable under the
inevitable budgetary perturbations as well as the occasional mission failures?
• Balance—Is the program structured to contain a mix of small, medium, and large missions
that together make the maximum progress toward the scientific goals envisioned by this decadal survey?
Can some of the scientific objectives be reached or approached via missions of opportunity and by means
of piggyback or secondary flights of experiments on other NASA missions?
• Robustness—Is the program robust in that it provides opportunities for the training and
development of the next generation of planetary scientists? Is it robust in that it lays the technological
foundation for a period longer than the present decade?
The criteria cited above are not orthogonal. “Balance” in various guises permeates the other three
criteria. For example, a balanced portfolio of missions enhances overall program stability; a balanced
portfolio of missions provides better assurance of a continuing stream of visible results. A balanced
portfolio also helps prevent large excursions in workforce demands and cost, therefore fitting more easily
into the relatively smooth year-to-year NASA budget.
Several factors can upset mission balance. Foremost among these is the lack of control and
predictability of mission costs. A 30 percent overrun in the cost of a mission costing several billion
dollars can distort the entire program of planetary science recommended in a given decadal survey. 6 Or,
as stated in stark language in a NRC report, An Assessment of Balance in NASA’s Science Programs:
“The major missions in space and Earth science are being executed at costs well in excess of the costs
estimated at the time when the missions were recommended in the National Research Council’s decadal
surveys for their disciplines. Consequently, the orderly planning process that has served the space and
Earth science communities well has been disrupted and the balance among large, medium and small
missions has been difficult to maintain.” 7 The report continues with the recommendation that NASA
should undertake independent, comprehensive and systematic evaluations of the costs to complete each of
its space and Earth science missions for the purpose of determining adequacy of budget and schedule.
NASA’s suite of planetary missions for the decade 2013-2022 should consist of a balanced
mix of Discovery, New Frontiers, and Flagship missions, enabling both a steady stream of new
discoveries and the capability to address larger challenges like sample return missions and outer
planet exploration. The program recommended below was designed to achieve an appropriate balance.
In order to prevent the balance among mission classes from becoming skewed, it is crucial that all
missions, particularly the most costly ones, be initiated with a good understanding of their probable costs.
The Cost and Technical Evaluation process used in this decadal survey was specifically designed to
address this issue by taking a realistic approach to cost estimation.
The cost containment record of AO-selected missions is relatively commendable, with a few
notable exceptions where the mission complexity or other factors was underestimated. The committee
endorses the recommendations in a recent NRC report that call on NASA to undertake the following
actions: 8
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