PARIS - European Space Agency (ESA) leaders appear to be closing in on a solution for a Mars lander initiative that would reconcile technological and science goals with available budgets.

A key objective of the planned 1.2 billion euro ($1.7 billion) ExoMars mission is to expand Europe's orbiter expertise and allow it to master new technologies - a rover; entry, descent and landing system (EDLS); and a deep drill.

However, doing this without exceeding the 850 million euro budget envelope member nations say they are willing to provide has proven difficult. After pushing back the mission to 2016 and scaling back the lander science package, ESA struck a deal with NASA this summer that would give the U.S. agency a key role in ExoMars as part of a long-term Mars road map ultimately culminating in a sample return flight Aerospace DAILY, July 10). However, this proved insufficient and planners were forced to consider eliminating a proposed fixed exobiology payload from the lander and shifting some of the key technology items to NASA - prompting member states to threaten to scuttle the mission altogether.

Now, ESA appears to have found a way around the problem by stretching out the ExoMars timeline and upping contributions to 1 billion euros - the figure the agency has long said is necessary to meet mission objectives. Under a proposal hammered out at an ESA Council meeting Oct. 7-8, the undertaking would be split into two parts - a lander/orbiter mission in 2016 and a rover mission in 2018, each with a significant NASA role.

ESA would provide the EDLS, the lander and orbiter for the 2016 flight, and NASA would furnish launch on an Atlas V 411 booster. The EDLS would be designed for a soft landing and the lander would be big enough - 600 kilograms (1,300 pounds) - to house a large battery-powered science payload. The orbiter would carry a NASA payload and be equipped with data relays that would serve both the 2016 and 2018 missions.

For the 2018 flight, Europe would supply a rover equipped with a deep drilling system along with a fixed exobiology payload. NASA would furnish the EDLS - equipped with a sky-crane touchdown system developed for other Mars missions - launch on an Atlas V 551 rocket, and possibly a second rover as well.

Mockup of ExoMars rover