G rowth in NASA’s science spending is expected to slow as the U.S. space agency strives to keep its human space exploration efforts on track in an increasingly constrained federal budget environment.

Until NASA’s 2007 budget request is released Feb. 6, only a select few inside NASA and the White House know the full extent of the agency’s plan for balancing the competing demands of building a new human reusable spacecraft, getting the space shuttle back in service to complete the international space station and maintaining robust programs in science and aeronautics.

But NASA officials made clear to the 3,100 astronomers gathered here Jan. 8-12 at the American Astronomical Society’s annual meeting that science spending will fall short of the growth targets NASA set around this time last year.

NASA Administrator Mike Griffin, in his keynote address, said the 5 percent to 7 percent annual growth in science spending in recent years cannot be sustained given the fiscal challenges facing by the United States.

“We are in a budget environment where that level of growth can’t be maintained, although science at NASA will still have growth,” Griffin said. “But we are all hurting.”

If the actual growth in NASA’s science spending has been good, the forecasted growth has been even better. The five-year budget NASA released last February showed science spending growing at a rate of 8 percent to 9 percent annually through the end of the decade.

NASA’s science stakeholders are quickly realizing that those sunny forecasts could soon give way to cloudy skies and cooler temperatures.

Joseph Alexander, who stepped down as president of the National Research Council’s Space Studies Board late last year, said keeping pace with inflation might be the best the NASA science community can expect in light of the pressure being brought to bear on discretionary spending throughout the federal budget.

“It’s hard to expect a growing budget,” Alexander said. “The best they might be able to expect is one that is continuous.”

Demands on NASA’s roughly $5.5 billion annual science budget have only been growing even as prospects for outside relief diminish in light of mounting space shuttle bills and the financial demands of building a new human-rated spacecraft and launchers.

As Griffin put it in his speech, “Our plate is not big enough to contain everything that was on it when I took office.”

The problem is especially acute in the NASA Science Mission Directorate’s astrophysics division, which has 14 astronomy missions in operation today and the agency’s most expensive satellite development effort — the James Webb Space Telescope.

In the past year, NASA realized it had underestimated by $1 billion the cost of designing and building Webb, prompting a restructuring of the program that has pushed the telescope’s launch date out to no earlier than 2013. NASA’s astrophysics division also is paying $10 million a month to keep a team in place to support a Hubble Space Telescope servicing mission targeted for late 2007, assuming NASA’s next space shuttle flight goes well.

Griffin told the astronomers gathered in Washington last week that Webb’s budget troubles would keep NASA from getting started on the planet-hunting Space Interferometry Mission. “We will delay it more than we would like because of the extra money we need for JWST,” he said referring to the Webb telescope by it initials.

Anne Kinney, director of the Science Mission Directorate’s astrophysics division, in a presentation the day before, showed a room full of restive astronomers a chart illustrating that the total projected cost of her current mission portfolio exceeded the most recent public budget forecasts for her division by as much as $500 million in some years.

“There’s just no doubt there are budgetary challenges,” Kinney told the group. “It’s a tough equation and it’s a tough thing to solve.”

Part of NASA’s solution appears to entail pushing the start of big, new, complicated astronomy missions out beyond the agency’s five-year budget horizon. Projected launch dates for both Space Interferometry Mission (SIM) and the black hole-hunting Laser Interferometer Space Antenna (LISA) have slipped to no earlier than 2015. Constellation-X, a proposed constellation of X-ray satellites, has been “pushed off into the indefinite future,” as Alexander put it. NASA has assigned that mission a launch date of no earlier than 2018.

“Everybody is nervous about what the 2007 budget will hold but that’s just the short-term worry,” said Kevin Marvel, the American Astronomical Society’s deputy executive director. “The realization that we are not going to be able to accomplish everything we set out to do in the decadal survey is only now really starting to sink in with people.”

Constellation-X and LISA ranked highly in the National Research Council’s decadal survey of astronomy priorities for 2000-2010. While SIM did not make the list, the mission was mentioned in the 2000 decadal survey as an important precursor to Terrestrial Planet Finder, a mission that ranked in the top five space astronomy initiatives but was nowhere to be seen on Kinney’s planning calendar.

Of the nine or so space astronomy mission included on the 2000 list, only two –the Gamma-ray Large Area Telescope and the Solar Dynamics Observatory — are expected to launch before the end of the decade.

Marvel said part of the problem with the 2000 decadal survey is that the astronomy community overestimated what NASA would be willing and able to spend and underestimated what the set of proposed missions would cost.

NASA officials heard from many astronomers at the meeting who expressed an interest in revisiting the stated priorities.

“Things have kind of changed on us,” incoming American Astronomical Society President Craig Wheeler told Griffin during a question and answer session following the administrator’s talk.

Marvel said the astronomy community has been discussing getting started on its next decadal survey in 2007, one year earlier than planned. Even with the head start, the new report would not be completed until 2009, Marvel said, in time, perhaps, to influence NASA’s 2011 budget decisions.

In the meantime, NASA officials said they intended to continue to look to the 2000 decadal survey for guidance and listen to input from advisory panels and the broader science community as spending priorities are set.

Comments: bberger@space.com