PARIS — European Space Agency (ESA) governments on Oct. 8 tentatively backed a proposal to join NASA in a two-step Mars exploration program that retains Europe’s goal of perfecting atmospheric entry, descent and landing technology, as well as developing a Mars lander and rover, ESA Director-General Jean-Jacques Dordain said.

Dordain said he told the 18-nation agency’s ruling council he expects to finalize an agreement with NASA by mid-November, by which time ESA should have a clearer idea of whether the new Mars-exploration scenario can be kept within the budget limits demanded of the old one.

“This agreement, once we get it signed with NASA, opens the door to new possibilities for us in planetary exploration,” Dordain said in an Oct. 9 interview. “The two missions we are working on with NASA permit us to retain all the goals for our ExoMars mission, while at the same time reducing the risk. Our member states indicated their support for the plan, and some even congratulated us on it.”

In addition to concluding the agreement with NASA, Dordain said ESA by mid-November will complete a review of whether the two missions — to be launched by NASA-provided Atlas 5 rockets in 2016 and 2018 — can be done within the budget ESA governments had set for the ExoMars mission.

ESA has had trouble securing sufficient funding for the ExoMars lander-rover mission. ESA member governments in late 2008 gave the agency a year to craft a mission that cost them less than 1 billion euros ($1.46 billion). These same governments had been able to secure no more than 850 million euros in commitments, which forced ESA to seek outside help and led to the current mission scenario.

The new program includes a 2016 launch of a 600-kilogram ESA lander that will include exobiology experiments and also permit ESA to test powered atmospheric descent and landing on the Mars surface.

The lander will not include nuclear batteries, which Dordain said would have added to mission cost and complexity. Instead, it will be powered by conventional batteries that will limit the lander’s operational life to “days, or perhaps a couple of weeks, but certainly not months,” Dordain said.

Adding the entry, descent and landing capability to the 2016 mission helped ESA overcome initial objections to the NASA deal by some European governments.

ESA also will provide a Mars telecommunications orbiter for the 2016 mission, with NASA supplying the electronics payload for the satellite.

The 2018 mission will feature ESA’s rover deployed to the Mars surface by the same Sky Crane system — with the rover, attached by chord to the descent module, gently lowered to the surface — that NASA plans to use for its large Mars Science Laboratory rover to be launched in 2011.

Dordain said ESA’s ExoMars mission would have combined three challenging elements — descent and landing, the lander package and the rover — all under ESA’s roof. The new program separates the lander from the rover and thereby reduces overall program risk, he said.

One industry official said Dordain apparently has succeeded in winning over the support of the agency’s major contributors — France, Germany, Italy and Britain — for the new Mars scenario. But this official said there are too many unknowns with respect to the final cost of the two-launch mission to be confident it will remain under a billion-euro price ceiling.

Because ESA is made up of 18 nations all looking out for the interest of their national industrial bases, ESA also has to make sure the Mars mission contracts are distributed to each nation in accordance with that nation’s contribution to the program.

At this point, Dordain said, he assumes that Italy will remain the biggest single contributor to the redesigned Mars effort, and that ESA will not need to abandon three years of design work on the rover and lander conducted under the earlier ExoMars program. 

Peter B. de Selding was the Paris bureau chief for SpaceNews.