WASHINGTON — NASA’s $5 billion funding request for science missions and related activities next year is $231 million less than what was projected at this time last year, but still represents a $500 million increase over 2010 driven in large part by the agency’s Earth science program, according to budget documents.

Ed Weiler, associate administrator for NASA’s Science Mission Directorate, said the 2012 spending plan demonstrates U.S. President Barack Obama’s commitment to Earth and space science even as the administration comes under increasing pressure to reduce federal spending.

“I believe this reflects a real vote of confidence by the administration in NASA science programs in these very austere times,” Weiler said during a Feb. 14 conference call with reporters. But the status and schedule of many of these programs remains uncertain due to Congress’ failure to rule on Obama’s budget request for 2011, which has left NASA and the rest of the federal government operating at 2010 spending levels under a continuing resolution that expires March 4.

Weiler warned that unless Congress approves the $5 billion request for NASA’s science programs in 2011, the 2012 spending plan could fall short of what is needed to continue operating the agency’s current missions while starting work on new ones that support the science community’s top priorities.

NASA’s $1.8 billion request for Earth science in 2012 is on par with what the agency had requested for 2011, representing a roughly $360 million increase over 2010. The budget would support ongoing development of missions including the Landsat Data Continuity Mission and U.S.-Japan Global Precipitation Measurement mission, both targeted for launch in 2013, while ramping up design work on others identified as key scientific priorities.

These priorities include the Icesat-2 ice-monitoring mission, whose budget would nearly triple, to $113.4 million; and the Soil Moisture Active-Passive (SMAP) soil moisture mapping mission, whose budget would nearly double, to $137.3 million. SMAP and Icesat-2 are slated to launch in 2014 and 2016, respectively.

The budget plan also supports early definition and design work on the two-satellite Desdyni vegetation and ice mapping mission, and on the Clarreo solar irradiance monitoring mission. However, because NASA cannot count on the 2011 funding increase it was hoping for in Earth science, the launch of both missions has pushed beyond the previously targeted 2017 date, budget documents show.

The Earth science budget also dramatically increases funding for a new series of low-cost Venture-class missions, from $6 million to $62 million, budget documents show.

NASA’s Planetary Science Division, meanwhile, would get $1.5 billion in 2012, about the same as projected at this time last year but $175 million more than was appropriated for 2010. However, that funding line would steadily decline through 2016, to just $1.25 billion, in the absence of major new development initiatives.

Weiler said NASA has known for some time that it does not have the money to fund robust programs that address each of the Planetary Science Division’s mission priorities. However, he said the division is eagerly awaiting the March 7 release of a new planetary science decadal survey that will help prioritize mission goals.

NASA is on track to launch three planetary missions this year, including the flagship-class Mars Science Laboratory, a $2.47 billion rover that exhausted funding reserves last year, leading to an $82 million funding shortfall between 2010 and 2012. Weiler said NASA shifted funds from within the Planetary Sciences Division to shore up the Mars rover mission’s reserves and “didn’t have to cancel or delay any programs to pick up that money.”

NASA’s astronomy and astrophysics budget is about $50 million less in 2012 than projected in last year’s funding request, which called for spending $1.1 billion this year on the James Webb Space Telescope (JWST) and other astronomy projects.

Under the new proposal, NASA would spend $683 million for astrophysics initiatives in 2012 while a separate funding line created last year for JWST would provide $375 million to continue development of the over-budget flagship astronomy mission.

“We have a smaller budget,” Jon Morse, director of NASA’s Astrophysics Division, told a Feb. 16 meeting of the NASA Advisory Council’s astrophysics subcommittee. He added that the division cannot afford to support all of its current on-orbit missions while embarking on new development efforts prioritized in the science community’s most recent astrophysics decadal survey released last year.

“The idea here is the missions in extended phase will be closed down in favor of getting the next ones going,” Morse said.

However, NASA is canceling its participation in the Joint Dark Energy Mission, a collaborative mission with the U.S. Department of Energy to investigate dark energy in the universe. NASA’s 2012 budget request instead allocates an unspecified level of funding for early studies of the Wide-Field Infrared Survey Telescope (WFIRST) mission, the top priority in the flagship-class category detailed in the decadal survey.

Morse said specific funding projections for WFIRST would be included in the president’s 2013 budget request.

NASA’s sun-science programs in the Heliophysics Division would see a modest increase over the next five years, starting with $622 million in 2012 and rising to $659 million by 2016, driven in part by a new Explorer-class mission to be selected in 2012.

The division will continue primary operations of its Solar Dynamics Observatory next year and work toward launch of the Radiation Belt Probes and Magnetospheric Multiscale missions in 2012 and 2015, respectively.

The request includes $52 million to continue formulating the division’s highest-priority large mission, Solar Probe Plus, which is slated to launch in 2018. It also continues work on the Solar Orbiter Collaboration mission, a NASA-European Space Agency project that will provide close-up views of the sun’s polar regions and its far side.