The US and European space agencies have announced a new partnership pairing a European cargo module with Nasa's Orion space capsule, which aims to take astronauts into deep space.
The agreement covers Orion's first planned mission, set for 2017, which will take the space-craft on an unmanned fly-by around the moon.
But Nasa has bigger goals for Orion, hoping it will one day take humans beyond low-earth orbit - for the first time since Eugene Cernan left the last footprints on the moon in 1972 - and ultimately to an asteroid and to Mars.
The US space agency said Orion's development may have started in the US but that its final shape will be determined by an international effort.
"Today you get to see the first step of a co-operation as we look beyond lower orbit," said William Gerstenmaier, Nasa's deputy director for manned exploration. "Space exploration has to be international," he emphasised during a news conference on Wednesday at the Johnson Space Centre.
The US, European and other space agencies already co-operate extensively at the International Space Station, while more ambitious missions further into space have remained national affairs. But a recent report by the US National Academy of Sciences concluded that Nasa's US$18 billion-a-year budget would not cover all its missions.