"The work is under way and we are finishing up the coordination," ESA spokesman Rene Pischel said. "The final agreement should be signed after the ESA ministerial conference in November."
The ExoMars program to send an orbiter to Mars in 2016 and a robot rover two years later was originally a joint NASA and ESA project but NASA has reduced its participation in the project out of funding concerns and said it wouldn't provide its Atlas carrier rocket for the launch.
Roscosmos, the Russian space agency, expressed an interest and offered to provide Proton carrier rockets for the two planned launches in exchange for full project membership.
Russia's participation in the project has been approved by the space council of the Russian Academy of Sciences, RIA Novosti reported Friday.