Box 1. Along for the ride?

NASA officials say that they don't want to go back to the Moon alone; they hope to get some help from international partners.

The space agency has already decided to take the lead in building the rockets, capsules and landers needed to get to the Moon's surface. But NASA hopes that it can get other contributions from foreign powers — perhaps a lunar rover or a module for the planned Moon base. "We're working with our international partners to figure out where they want to play in terms of exploration," says Shana Dale, the agency's deputy administrator.

Although NASA has started consulting with allies from around the world as part of its Global Exploration Strategy, not everyone is convinced by its overtures. "I personally feel a little bit disappointed," says Jean-Michel Desobeau of Arianespace, based in Paris. As an executive at Europe's largest commercial launch company, Desobeau thinks that NASA's decision to exclude foreign powers from its high-profile rocket- and capsule-development programmes may lead to resentment among these countries. "Europe, Russia and China want to be more than just a subcontractor," he says.

An even greater political obstacle orbits high above Earth. The International Space Station — the centrepiece of European, Russian and Japanese human spaceflight programmes — is still waiting for key modules to be delivered. NASA has committed to finishing the space station by 2010, but intends to bring its involvement to an end after 2016, allowing it to focus its resources on the Moon. Keeping the space station supplied and ferrying crews back and forth will be a significant challenge to the remaining partners, of which only Russia has the capacity to fly humans into space.

The prospective American withdrawal has led to some wringing their hands, and could make other countries hesitant to join yet another NASA-led project.

It will take a little diplomacy to move the vision, says Roger Blandford of Stanford University in California. Blandford believes that, just like modern particle accelerators and fusion machines, a programme as ambitious as the vision requires collaboration. "Everybody has to band together," he says. "The only way that any of this makes sense economically is as a global enterprise."