Congratulations are due to the European Space Agency (ESA) and Thales Alenia Space for finally getting the ExoMars mission under full-fledged contract.

For five years, ESA and the company have somehow kept development of the mission, featuring launches to the red planet in 2016 and 2018, on track using minimal, incremental funding tranches. Thales Alenia Space deserves special recognition for forging ahead despite the contractual uncertainty: Missing the first window — due to solar system dynamics, Mars launch opportunities come only once every two years — would badly disrupt the program since the 2018 mission will rely on a data-relay orbiter slated to launch in 2016.

ExoMars has already experienced its share of challenges, including opposition from key ESA members and the partial withdrawal of NASA, which originally was supposed to launch both missions. NASA has been replaced in that capacity by Russia, which is supplying Proton rockets and also is building a lander and nuclear battery for the 2018 mission. Just last year, even with Russia on board, ExoMars supporters were giving the mission a fifty-fifty chance of survival.

The newly signed contract, valued at 230 million euros ($300 million), or less than half of what ESA has spent on the program to date, does not guarantee the 2016 launch date for the first mission, which in addition to the orbiter also will feature Europe’s first Mars entry, landing and descent package. Plenty can go wrong on program of this complexity. But the contract finally puts the 2016 mission on a stable financial footing, allowing ESA to focus on putting together the elements of the 2018 mission, including finding the 150 million euros needed to complete the necessary financing package. That’s a big relief to a planetary science community that in recent years has had more than enough to worry about.