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Mars 2020
The decadal survey process, which has recommended missions like Mars 2020 (above), may not be well-suited to human spaceflight. (credit: NASA/JPL-Caltech)

Would a decadal survey work for human space exploration?

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The National Research Council decadal science strategy surveys—or more colloquially known as the decadal surveys or just the decadals—are signature products of the National Academies.[1] There is probably no other space science advisory product that has earned the attention and reputation, year after year, or had an impact to rival that of the decadals. If these strategy studies have been so successful for the space sciences, one might logically ask whether the same process could and should be applied to the area of human spaceflight. This article explores the questions of what constitutes a decadal survey and what makes them effective, all in order to consider whether the process is transferable to other areas such as human space exploration.

The origins of the decadals

In 1962, the National Academy of Sciences Committee on Science and Public Policy (COSPUP) formed the Panel on Astronomical Facilities to assess the status and future needs for new ground-based astronomical facilities in the US. The committee’s 1964 report considered the state of observing facilities and as well as trends in graduate student enrollment in astronomy and the implications for demand for astronomy facilities in the US. Five years later, COSPUP formed a new Astronomy Survey Committee that had a substantially broader and more ambitious charge: namely, to review the state of US astronomy, identify the most important scientific problems in the field, and recommend priorities for both ground-based and space astronomy for the coming decade. The scope of the new study—reviewing progress over the past decade and recommending priorities for the next decade—led to the study’s popular name of decadal survey.

Subsequent astronomy and astrophysics decadal surveys were completed about every ten years through 2010, and a new survey—“Astro 2020”—is currently under way (see “Selecting the next great space observatory”, The Space Review, January 21, 2019). All of the surveys share the following attributes:

  • Broad disciplinary scope covering an entire scientific field,
  • A long time horizon that examines accomplishments and advances over the previous decade and scientific priorities for the next decade,
  • Inclusive participation by a large fraction of the relevant scientific community,
  • Explicit priorities for new projects and facilities, including consideration of their estimated costs and recommended schedules, and
  • Enabling capabilities such as workforce and training, computation and data handling, institutional factors, and various dimensions of balance.

In 2000, NASA requested two new surveys—one for Solar and Space Physics (also known as heliophysics) and one for Solar System Exploration. These first decadal surveys to reach beyond the field of astronomy were published in 2003. Like their astronomical predecessors, the new decadals enjoyed administration and congressional attention, and NASA worked to follow their recommendations to the extent that agency budgets permitted.

The decadal science strategy surveys have enjoyed remarkable acceptance, respect, and staying power.

In 2003, NASA and NOAA asked the National Academies to further expand the use of decadal surveys to the field of Earth observations and applications from space. This survey was different from its predecessors in several ways. First, it encompassed a field that has a large applied science dimension that builds on and extends beyond the basic research aspects of the Earth sciences. Second, the Earth science community was considered to be significantly more diverse, both topically and culturally, than the space science disciplines that were considered in the prior surveys. Furthermore, the community was initially hesitant to embrace the idea of a decadal survey for the field and also was demoralized by recent budget cuts from a Bush Administration that was not especially supportive of the Earth sciences. One of the survey’s eventual successes was the fact that the undertaking did help bring the community together and get its members to take a more integrated view of their field and to encourage Congress to support the endeavor.

In 2010, the National Academies conducted the first decadal survey covering the scientific aspects of human spaceflight, and that survey report was completed in 2011.[2] The NASA office responsible for managing life and physical science in the microgravity environment of laboratories on the International Space Station appeared to be striving to respond to the survey recommendations as positively as limited budgets would permit.

As of early 2019 there have been six decadals in astronomy (most recently published in 2010), two in solar system exploration (most recently published in 2011), two in solar and space physics (most recently published in 2013), and two in Earth observations from space (most recently published in 2018.) And as noted above, the National Academies published the first decadal survey for life and physical microgravity sciences in 2011.[3]

Why the decadals work

The decadal science strategy surveys have enjoyed remarkable acceptance, respect, and staying power. Even though their recommendations have often been overly optimistic and their execution has taken longer than the decade for which they have been framed, both NASA and Congress have tended to view them as the best advice available. Nearly all spaceflight program initiatives recommended by the surveys in the 1990s or beyond have been adopted or carried on for study and later selection.

The more a decadal survey is directed at a relatively contained ensemble of sub-disciplines and communities, the easier and more tractable the effort is likely to be.

This record of success can be ascribed to several key aspects of the surveys. First, the broad participation by a substantial fraction of the relevant research community and the intense deliberations that lead to the surveys’ conclusions provide a kind of heft that makes them very difficult to discount or disregard. A survey committee’s membership is drawn from a broad cross section of the relevant research community—including not only scientists but also engineers and experts with management and policy experience—so that there are ample opportunities to correct for persons who might be pushing a single agenda or who might not be expert in all the dimensions of the work at hand. Policy-makers recognize that the results of the surveys represent about as good a community-wide consensus as can be obtained. And just as importantly, the broad participation generates buy-in across the community so that researchers feel a sense of ownership in the survey results and are usually likely to stand behind the results.

Second, the recommendations in the survey reports are derived from a fundamental scientific assessment that first defines a set of scientific goals from which implementation priorities are derived. The surveys don’t first ask “What do we want to build?” or “How much money do we expect?” and then build a program around those estimates. Of course, in the cold light of day it’s hard to imagine that such considerations don’t enter into committee members’ thinking, but the logic for the survey conclusions is built first on the science. And the more carefully and coherently that train of scientific arguments is built, the more successful the final result will be. So the survey committees first ask their colleagues, “What have been the major scientific developments over the past decade; what are the most pressing scientific problems to be tackled in the coming decade; and what do we need to do to make progress in answering those questions?” Having filled in the scientific outline, they then proceed to translate the scientific strategy into an implementation strategy.

The third powerful attribute of the surveys is that they do recommend specific priorities and recommend implementation actions in priority order. To do so requires the committees to make difficult choices from which there are inevitably winners and losers. Recent surveys have also proposed decision rules, which recommend how NASA should weigh decisions when unforeseen implementation problems arise or other issues force managers to make tradeoffs or choose between alternative paths. Thus, the surveys demonstrate a sense of seriousness about the recommendations and a willingness on the part of the scientific community to take ownership of their recommendations. And of course, having such an explicit recommended strategy certainly gives decision makers and managers a basis from which to work if they so choose. They also appreciate the fact that having such a solid outside set of recommendations often provides excellent cover that permits them to point to a decadal survey when justifying a decision.

Will a decadal survey work for human spaceflight?

The more a decadal survey is directed at a relatively contained ensemble of sub-disciplines and communities, the easier and more tractable the effort is likely to be. A relatively homogeneous agency mission and stakeholder community should be a ready candidate for a decadal survey if it will have the attributes noted above.[4] However, as mission and stakeholder diversity increases—for example, by combining scientific research with service or operational or regulatory or geopolitical roles—the endeavor can become increasingly complex. This kind if diversity especially impacts the outreach and consensus-building aspects of a survey.

The community for human spaceflight is probably too narrow for a decadal survey. No larger community exists in the way that it does for the space sciences where scientists, technologists, and students pursue their work in many academic, private sector, and government laboratories.

The discussion above would suggest that the decadal survey process is not applicable to the area of human spaceflight for at least two reasons. First, the mission of human spaceflight is not at all narrowly defined or distinct, and one might argue that the mission is not well defined at all. Ever since the end of the Apollo program, efforts to define a clear set of goals or a singular rationale for human spaceflight[5] have struggled and have usually ended up with diverse purposes that include national security, technology, international relations, science, education, and others. That is a lot for a decadal survey to get its arms around. In contrast, all of the successful surveys described above have had a single mission focus—science.

Second, the community for human spaceflight is probably too narrow. One might even argue that there is no human spaceflight community outside of certain elements of NASA—notably Johnson Space Center, Marshall Space Flight Center, and Kennedy Space Center—and the aerospace firms that support those centers and build the necessary hardware. No larger community exists in the way that it does for the space sciences where scientists, technologists, and students pursue their work in many academic, private sector, and government laboratories. To put it another way, in the sciences there is an extramural community of participants who feel a sense of ownership for the endeavor and who embrace the opportunity to debate priorities and recommend strategies to an agency that they view as delivering a program on their behalf. There is no comparable community, outside of NASA and its contractors, that feels an ownership of human space exploration. Instead, the developers, providers, and users are the same, and there is no broader outside user community.

This is by no means an argument that science is better than human exploration; it is just different from the perspective of its community of participants. Consequently, the great diversity of purposes for human exploration plus the narrowness of its major participants lead me to conclude that trying to accomplish a classical decadal survey for human spaceflight would be an enormous, and probably intractable, challenge.


  1. The National Academies of Sciences, Engineering, and Medicine refer collectively to themselves and their operating units through which they develop advice to the government as the National Academies. The operating units were formerly known as the National Research Council.
  2. National Research Council, “Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era,” Washington, DC, The National Academies Press, 2011.
  3. Information about all the decadal surveys is available on the Space Studies Board website.
  4. There have been decadal surveys in other areas, e.g. ocean sciences, materials research, and civil aeronautics, but like the space science surveys they have all focused on specific research and technology topics.
  5. For example, see National Research Council, “Pathways to Exploration: Rationales and Approaches for a U.S. Program of Human Space Exploration” (The National Academies Press, Washington, DC, 2014); National Research Council, “NASA’s Strategic Direction and the Need for a National Consensus” (The National Academies Press Washington, DC, 2012); and National Research Council, “America's Future in Space: Aligning the Civil Space Program with National Needs” (The National Academies Press, Washington, DC, 2009).

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