Mark Carreau Houston and Amy Svitak Paris

Lacking the ability to finance costly manned space missions on its own, Europe has long had ambitions to serve as a junior partner in a collaborative campaign that would send astronauts beyond low-Earth orbit.

In January, the European Space Agency (ESA) found the right partner in NASA when the U.S. space agency announced plans to put Europe on the critical path for early development of its Orion/Multi-Purpose Crew Vehicle, a vessel designed for mission to cislunar space, near-Earth asteroids and perhaps Mars.

Under the agreement announced Jan. 16, ESA will leverage its International Space Station experience with the Automated Transfer Vehicle (ATV) into a critical-path responsibility: an ATV-derived service module for one and possibly two test flights of the Orion atop the new Space Launch System (SLS) that NASA is developing for manned exploration of the moon and beyond.

Top officials at both agencies credit their long-standing partnership in the 15-nation International Space Station (ISS) as the basis of a budding alliance that could place European astronauts aboard future U.S.-led deep-space missions. Specifically, ESA's pledge to provide five ATV cargo resupply missions to the six-person orbiting space lab between 2008-14, a barter agreement that covers Europe's share of the ISS common operating costs through 2017.

Instead of continuing ATV production, elements of the EADS-Astrium ATV will be adapted for NASA's Exploration Space Mission-1, an unpiloted 2017 test flight of the Orion capsule and an initial version of the SLS on a flight to the lunar environs, says William Gerstenmaier, NASA associate administrator for human exploration and operations. Spare service module components developed under the new agreement, if available, could be rededicated to the service module portion of Exploration Space Mission-2, a 2021 piloted test of the Orion and SLS on a similar trajectory.

The preliminaries, including hardware responsibilities and contractor roles, have been in the works for months. ESA ministers pledged a 60% commitment of their cost—about €455 million ($600 million) in late 2012. The balance could come in mid-2014 if ESA's 20 member states commit the remaining money in a new multi-year spending plan, says Thomas Reiter, a former astronaut who heads ESA's human spaceflight and operations division.

“This is the normal process,” Reiter says. “There is a clear path forward and a clear commitment on a basic programmatic ground for the time until the end of this decade.”