Plans for Gulf war II were first rolled out on the boardroom table of a neo-conservative thinktank in Washington a couple of years before George W Bush was elected. That much we already know. What has been overlooked is that the same group of Republican party strategists proposed another target for military occupation - space.

"For US armed forces to continue to assert military pre-eminence, control of space ... must be an essential element of our military strategy," wrote the authors of Rebuilding America's Defenses.

Defense secretary Donald Rumsfeld later chaired a high-level space commission, which concluded that military control of space was the only way for America to avoid a "space Pearl Harbor". Paul Wolfowitz, his deputy, now suggests that space can provide "higher leverage" for US Defense spending: "It truly is the ultimate high ground," he argues.

If Bush wins a second term, the weaponization of space is expected to get under way, finally realizing Ronald Reagan's "Star Wars" dream. The 1967 Outer Space Treaty, which outlaws the use of weapons in orbit, will go the same way as the anti-ballistic missile treaty - another strand of global governance unraveled in pursuit of the war on terror.

Given all this, what are we to make of President Bush's sudden enthusiasm for sending astronauts to Mars? Six weeks ago, the panoramic shots of the Martian landscape taken by Nasa's Spirit probe provided the perfect backdrop for an election-year speech. Bush explicitly laid claim to JFK's Apollo legacy, by emphasizing America's destiny to explore the final frontier: "We do not know where this journey will end, yet we know this: human beings are headed into the cosmos."

Yet it seems likely that darker motives lurk behind Bush's firm-jawed pose. Against the backdrop of the biggest increase in US Defense spending for over 20 years - reaching $399bn in 2004 - there is already a discernable shift in relations between the US Department of Defense and Nasa. America's civilian and military space programs are converging, and the extra funding which Bush has proposed in order to reach Mars is likely to accelerate this convergence. Nasa boss Sean O'Keefe is now widely tipped to be Defense secretary in Bush's second term.

Bush's vision of Americans on Mars comes with a hefty price tag attached, and it remains to be seen whether the electorate will be willing to pay. But with China now aggressively pursuing its own space program and aiming to send an astronaut to the moon by 2010, space is moving up America's foreign policy agenda.

A new chapter in the space race is starting to unfold. The announcement of a Mars mission may be little more than a curtain raiser for increased spending on military space.

Jean-Jacques Dordain, head of the European Space Agency, says: "For the United States, space is an instrument of domination. Europe should be proposing a different model: space as a public good."

Dordain sums up the way in which US and European ambitions for space have diverged. This gulf became apparent over plans for Galileo, the European satellite positioning system, which finally received a green light last week - despite frequent US attempts to kill the project.

Until now, the US-run GPS system has enjoyed a global monopoly, giving the Pentagon ultimate control of every satellite navigation system - right down to the route planners in cars. When Galileo goes live in 2008, it will not only be a superior system in technological terms, but the US military will no longer have its finger on the on-off switch. Galileo will be a civilian-controlled system, the product of collaboration between scientists and industrialists from 18 countries, including China.

This approach can be traced back to the founding charter of the European Space Agency, which commits each of its 15 members to use space for peaceful purposes. The European partners are now gearing up for Aurora, a 25-year program of scientific missions to Mars and beyond.

And what of Britain's role? As with Iraq, it seems unlikely that Britain will be able to restrain a US administration intent on strategic control of space.

In the new space race, the real battle will be to define what space is for: collaboration or control; weapons or probes; ultimately, war or peace? Britain must decide which vision it prefers.

· James Wilsdon is head of strategy at Demos and co-author of 'Masters of the Universe: Science, politics, and the new space race' www.demos.co.uk

© Guardian Newspapers Limited 2004

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