WASHINGTON — The ruling council of the 18-nation European Space Agency (ESA) is expected to meet Oct. 7-8 in Paris to hear ESA Director-General Jean-Jacques Dordain make the case that a long-term cooperation on Mars exploration with NASA is worth the sacrifice in European autonomy.

Dordain and ESA Science Director David Southwood specifically will propose that the agency’s ExoMars lander and rover project, which ESA governments have had difficulty funding, be divided into two or more missions conducted in partnership with NASA.

NASA officials say the forthcoming decision is a pivotal one for the joint effort, which would span launch opportunities slated for 2016, 2018 and 2020, with landers and orbiters conducting astrobiological, geological, geophysical and other high-priority investigations and leading to the return of samples from Mars in the 2020s.

“October is going to be critical for us in terms of whether or not we’re really on track,” said Michael Meyer, NASA chief scientist for Mars exploration. “By the end of this year, we should know whether we have a viable joint mission, or not.”

Discussions between NASA and ESA began in December 2008, driven by the ESA Ministerial Council’s recommendation to seek international cooperation to complete the ExoMars mission and to prepare further Mars robotic exploration missions. At the same time, NASA was reassessing its Mars Exploration Program portfolio after the launch of its $2 billion-plus Mars Science Laboratory mission was delayed from 2009 to 2011.

NASA officials are confident Europe will move forward with plans to further a cooperative ESA-NASA Mars program. During a Sept. 25 luncheon in Washington, Ed Weiler, NASA associate administrator for science, said a conversation with Southwood the previous day had yielded positive results.

“[B]ottom line is we are looking at a Mars program starting in 2016 that every single mission will be joint ESA/NASA,” Weiler said. “I think the trend is more and more collaboration … we’re talking about getting extra value by getting more value out of a mission.”

But ESA managers have already met resistance to the plan from Italy, the putative ExoMars lead investor, and from other ESA nations that say ExoMars no longer bears any relation to what they thought they agreed to build.

ExoMars has gone through several iterations. The latest was a mission to be launched in 2016 that would allow ESA to prove its capability in entry, landing and descent technology in addition to carrying a rover and a drill-equipped lander.

Meyer said ESA would provide a telecommunications relay capability on a Mars orbiter for a NASA-launched mission in 2016. NASA would launch a second mission in 2018 that would carry the ExoMars rover, and possibly a lander. Meyer said launch vehicles for the 2018 mission are under discussion. One possibility is a United Launch Alliance Atlas 5 with two solid-rocket boosters and a Centaur upper stage. Meyer said launch aboard Europe’s Ariane 5 is also being considered.

“It’s a good enough opportunity in 2018 that it could be launched on an Ariane 5,” he said. In the meantime, ESA would need to scrap, for now, its goal of testing entry, descent and landing technology with ExoMars, although Meyer said a demonstration of this capability will be part of the 2016 mission, according to ESA officials.

European government and industry officials say that, even if the ESA-NASA scenario is not approved, it is not clear that ExoMars will be launched at all because of its ongoing budget difficulties.

ESA governments had agreed in November 2008 to give ExoMars managers until the end of 2009 to craft a mission that could meet the original technology goals and include a substantial science package — all for 850 million euros, or $1.2 billion at current exchange rates.

To that figure would be added about 150 million euros to be financed by individual nations’ laboratories, which would furnish the science experiments.

ESA had trouble fitting the mission as approved into the budget ceiling, and set off on a search for a partner — NASA and Russia were approached — willing to make a big contribution in kind. That search led to the current proposal. But if ESA opts to scrap ExoMars, NASA is likely to push ahead on its own.

“We think we can do a trace-gas mission on the Scout level if this whole thing falls through,” Meyer said, referring to NASA’s program of cost-capped, competitively selected Mars Scout missions. “We don’t think it will; it looks like ESA and NASA have similar goals, which is always a great way to start a relationship.”

Jim Green, NASA planetary science division director, said a Mars sample return mission is a natural venue for international collaboration. “What we really are talking about is a program where we both work together … and there are tremendous opportunities in science that we can gain from that,” Green said. “Even if we had the finances, we’d still like to do it as an international endeavor.”


Peter B. de Selding contributed to this article from Paris.