A concept of the European Space Agency's ExoMars Rover.

PARIS — The European Space Agency (ESA) has issued stop-work orders on contracts for its billion-dollar ExoMars program pending negotiations with NASA on how U.S. and European Mars rovers planned for launch in 2018 might be merged into one, ESA Science Director David Southwood said April 20.

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