WASHINGTON — In a move NASA is counting on to deflect criticism of its decision to pull out of the European ExoMars program, the U.S. space agency plans to use part of its downsized Mars budget to cobble together a cheaper set of missions that would meld science and human spaceflight goals.

NASA Administrator Charles Bolden said Feb. 13 he has tasked the Science Mission Directorate to work with the Human Exploration and Operation Mission Directorate and the agency’s chief technologist to craft an “integrated strategy to ensure that the next steps for Mars exploration will support science as well as human exploration goals, and potentially take advantage of the 2018-2020 exploration window.”

NASA had planned to join the European Space Agency in 2018 on the second of two robotic Mars missions designed to set the stage for returning samples from the red planet in the 2020s.

But with NASA’s Mars budget slated to drop nearly 40 percent next year, followed by further double-digit declines in 2014 and 2015, NASA can no longer afford to embark on a multibillion-dollar Mars sample-return campaign.

Part of the $226 million the White House is proposing to cut from the Mars budget in 2013 would be used to cover a $109 million increase for the massively overbudget James Webb Space Telescope and fund much more modest raises for Earth science and heliophysics.

“We’re a lower priority than some of the other things,” James Green, NASA’s director of planetary science, told Space News in a Feb. 15 interview.

NASA’s Planetary Science Division would use the $360 million the agency is seeking for Mars exploration in 2013 to fund the continued operation of several Mars spacecraft, including the $2.5 billion Mars Science Laboratory rover landing in August, and press ahead with the Mars Atmosphere and Volatile Evolution (MAVEN) orbiter launching late next year.

But the Mars mission manifest gets murkier after that. Mars InSight, one of three candidate Discovery missions currently under study, would launch in 2016 if it can beat out its competition in a final down select scheduled for June.

Whether NASA launches a spacecraft toward Mars in 2018 will depend on what comes out of the integrated planning effort, dubbed Mars Next Decade, that the agency plans to kick off this year with $4 million in funding that would grow to $62 million next year.

Former astronaut John Grunsfeld, who took over as NASA associate administrator for science in January, said the envisioned Mars missions would be cross-agency efforts supported by NASA’s science, human spaceflight and space technology divisions. Instead of a probe designed solely for studying atmospheric or geological phenomena, the mission might also track radiation levels in interplanetary space and on the martian surface — data needed to prepare for human exploration, Grunsfeld told reporters Feb. 13.

He said NASA will look at missions that could be done for roughly $700 million, the amount NASA spent on the 2005 Mars Reconnaissance Orbiter and expects to spend on MAVEN.

The team NASA is assembling for the Mars reboot is scheduled to meet here Feb. 27 with the Mars Exploration Program Analysis Group and send a delegation to the Lunar and Planetary Science Conference being held March 19-23 in Texas.

NASA’s backup plan did little to assuage the staunchest Mars exploration advocates.

“If this budget is allowed to stand, the United States will walk away from decades of greatness in space science and exploration,” Bill Nye, director of the Pasadena, Calif.-based Planetary Society, said.

Rep. Adam Schiff (D-Calif.), a member of the House Appropriations subcommittee that decides the NASA budget each year, also blasted the cuts, which would fall especially heavy on the Jet Propulsion Laboratory in his district.

“I intend to fight this misguided proposal tooth and nail,” Schiff said.

Meanwhile, Green said NASA will be ordering its contractors to stop work on five instruments the agency had been planning to contribute to the 2016 ExoMars Trace Gas Orbiter mission.

“The teams will now be ordered to cease work on those instruments, most of which are at or near the preliminary design review,” Green told Space News. He said the $45 million NASA has spent on its instruments need not go to waste; scientists could incorporate the designs, all but one of which has passed preliminary design review, for other missions.

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.