NAPLES, Italy — The 20-nation European Space Agency (ESA) approved a cooperation arrangement with Russia Nov. 19 under which the Russian space agency, Roscosmos, will provide two Proton rockets to launch what has become the Euro-Russian ExoMars mission in 2016 and 2018, according to ESA officials.

Frederic Nordlund, ESA’s director of international relations, said the agreement would be finalized in the coming days and that its principal characteristics are already known and accepted by both sides.

ESA’s ruling council approved the Russian partnership here in advance of a two-day meeting of ESA government ministers during which other pieces of ExoMars’ financing were likely to be discussed.

ESA is depending on Russia to save the life of ExoMars, on which ESA governments have already spent more than 400 million euros ($520 million).

Comprising a telecommunications orbiter with a NASA-provided antenna, and an entry, descent and landing module in 2016, plus an ESA-built rover for launch in 2018, ExoMars is now expected to cost ESA about 1.2 billion euros after accounting for the two Roscosmos-provided Proton launches of the two missions.

Russia will provide an instrument for the 2016 telecommunications orbiter and will have principal responsibility for a landing module for the 2018 mission, in addition to providing an experiment aboard the ESA rover.

The agency is about 350 million euros short of what it needs for ExoMars.

Among several potential sources of cash for the mission, ESA has said that a portion of the ESA dues paid by new members Poland and Romania might be spent on ExoMars.

The agency has also said Russia’s Proton might be used to launch Europe’s Juice mission to Jupiter in 2022, saving ESA’s science program some 170 million euros. A portion of these savings would be used to take part in Russia’s Ganymede mission to Jupiter’s largest moon, with the major share covering the current ExoMars shortfall.

ESA managers are also counting on their science program — which is run independently and is not subject to ESA executive edict on mission choice — to contribute 50 million euros to ExoMars in consideration of ExoMars’ scientific merit.

Europe’s Science Program Committee was given an update on what ESA needs for ExoMars the week of Nov. 12 and will decide at its next meeting, in February, whether to accept the request.

One problem, according to a European science official, is that the science program under normal circumstances would not need to finance the launch of Juice until 2020. If a free Proton launch is secured as part of a Euro-Russian cooperative program on exploration of the Jupiter system, and the savings are used to fund ExoMars, these monies would need to be furnished in 2016, if not earlier.

Nordlund said the agreement on a third Proton rocket as part of a collaborative exploration of Juice is a separate undertaking and not part of the ExoMars package agreed to by the two sides up to now.

The European science official said ESA has decided to line up all the unconfirmed contributions it can work on its own before presenting the Science Program Committee with a final request. At that point, the committee could be in the position — with the accompanying pressure — of saving or scuttling ExoMars.

Peter B. de Selding was the Paris Bureau Chief for SpaceNews.