WASHINGTON — The so-called decadal surveys that set priorities for NASA’s $5 billion-per-year science portfolio are the science community’s best chance to influence the internal White House budget negotiations affecting specific missions, NASA’s chief scientist told a National Research Council panel here Aug. 26.

Annual budget negotiations between the White House and NASA are conducted in secret, and the results released publicly — and to Congress — only after the tough calls have been made. Outsiders are not consulted, even when falling budgets precipitate major changes, as happened in 2012 when the White House took NASA off the international ExoMars sample-caching mission that addressed a top planetary science objective.

However dramatic the trades NASA is considering, “we can’t come back to you and be honest about the trade space we’re working with,” Ellen Stofan, NASA’s chief scientist, told the NRC-chartered Survey of Surveys Aug. 26. “We’re not allowed to, that’s the way it is.”

For that reason, Stoffan said, scientists need to “give NASA … a flexible path to use the decadals.” She offered the 2011 decadal survey of NASA’s planetary science program as an example. That document, “Visions and Voyages for Planetary Science 2013-2022,” provided guidance tailored to different budget scenarios, including a decline below anticipated levels.

The ad hoc Survey of Surveys committee was convened this year to consider lessons learned from recent decadal surveys, and whether any tweaks are required to either the survey process or the content of the final document produced by the community for NASA.

Each of NASA’s four science divisions — planetary, astrophysics, heliophysics and Earth — is guided by its own decadal survey, prepared by an NRC panel composed of scientists who are experts in the field. Stoffan, a planetary scientist by training, helped write the planetary science decadal.

All four divisions were represented on the 13-member Survey of Surveys committee, chaired by Alan Dressler, an astronomer at the Carnegie Institute for Science in Pasadena, California. The committee is scheduled to produce a report in June, about six months after its third and final meeting, which is scheduled for Dec. 8 in Irvine, California.

Not all of the presenters shared Stoffan’s view that decadal surveys must always prescribe specific options for different budgetary scenarios.

Joel Parriott, head of public policy for the Washington-based American Astronomical Society, told the NRC panel it is tempting for scientists to overshare in a decadal survey, especially because the congressional staffers who draft NASA’s annual spending bills want as much detail as possible.

However, “the downside to including everything is you give somebody with ulterior motives a recipe for cutting,” said Parriott, who previously served for 10 years at the White House Office of Management and Budget (OMB).

Parriott said there is something to be said for an “aspirational” survey that abandons any pretense of predicting what might happen with federal budgets, sets out big-picture science goals “and let the chips fall where they may.”

“When I was at OMB, agency program managers who were perceived by policymakers as being competent and spending taxpayer dollars well got a lot of latitude,” Parriott said.

One NASA manager invited to speak before the committee had trouble envisioning a purely aspirational decadal survey.

“I can’t imagine us not asking, as part of the charge, to recommend a program for the next decade that fits within the anticipated budgets,” said Paul Hertz, director of NASA’s Astrophysics Division.

Another senior NASA executive said it is inherently futile to worry too much about costs in a document intended to help the agency accomplish never-before-attempted science.

“We don’t know the costs of the missions, and we will not know them well until significant amounts of money are spent for each individual mission,” Michael Freilich, director of NASA’s Earth Science Division, told the NRC panel. “To think that somehow we can track that problem algorithmically or some other way by a really good group of people working on a decadal survey in their spare time … I think that that’s fanciful.”

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.