BORDEAUX, France — Europe’s ExoMars mission to deliver a telecommunications orbiter, a short-duration descent and landing module and a rover to Mars on Russia-provided launches in 2016 and 2018 has cleared a key hurdle with the completion of the heat shields for the 2016 mission.

The shields, ranging from 8 to 14 millimeters in thickness and made up of 180 cork-resin composite tiles, were scheduled to leave Airbus Defence and Space’s plant here for delivery to the ExoMars prime contractor, Thales Alenia Space.

Airbus and Thales Alenia Space officials said during a July 7 briefing here that the ExoMars 2016 mission, with a planned launch in January 2016, remains a challenge for industry, but that the development status of the principal mission components is consistent with a launch in less than 18 months.

ExoMars began as a U.S.-European joint program, but NASA pulled out most of its involvement, including two Atlas rockets, pleading budget pressures. The U.S. agency remains involved with its communications payload.

ESA sought assistance from the Russian space agency, Roscosmos, which has agreed to provide two Proton heavy-lift vehicles and has become a full partner in the ExoMars science mission.

Airbus officials here said the delivery of the ExoMars shields leaves them without a re-entry program. After the 1998 Atmospheric Reentry Demonstrator test flight, the 2008 shields for the ill-fated Beagle 2 Mars lander and the 2005 landing on Saturn’s moon, Titan, company officials said the next logical step is a sample-return mission.

No such mission is currently on the schedule of the European Space Agency, however, leaving Airbus to continue research and development through small programs funded by the European Commission.

Thales Alenia Space is building the Trace Gas Orbiter for the 2016 mission as well as the payload components for the entry, descent and landing module with the Airbus heat shields. Because of the start-and-stop nature of early ExoMars funding following intermittent support from ESA governments, it has always been the 2016 mission that has been the most difficult.

At one point, several ESA governments expressed doubt about whether the Thales Alenia Space-led consortium could complete the work to make the 2016 launch date. ESA Director-General Jean-Jacques Dordain was able to keep the program alive through small funding increments in part by arguing that without ExoMars, ESA does not have an exploration program.

The critical design review for the mission was completed in April. An interim system qualification review is scheduled for mid-2015. Assembly, integration and test of the orbiter and the descent module are underway.

By September 2015, the flight acceptance review should be completed, followed by the final flight readiness review late that year and a shipment to Russia’s Baikonur Cosmodrome spaceport in Kazakhstan for a four-week campaign ending in a January launch.

The landing module is scheduled to be released from the orbiter three days before the package arrives in Mars orbit. Without nuclear power — an agreement with the Russians to provide nuclear heaters fell through owing to technology-export restrictions — the lander is expected to survive only two days.

The 80-kilogram, 2.4-meter-diameter front shield is built to permit experiments inside the lander to remain operational even as outside temperatures on the shield reach 1,800 degrees Celsius as it enters the Mars atmosphere at a speed of 21,000 kilometers per hour, said Bart Reijnen, Airbus’ senior vice president for orbital systems and space exploration.

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