Washington - The US should abandon its "flexible approach" to human missions beyond Earth, set Mars as its ultimate goal and open the door to China among other potential partners, a review of the human space flight programme said on Wednesday.The National Research Council report, commissioned by the US space agency Nasa, recommends a stepping stone approach toward Mars that builds technological know-how through a series of well-defined preliminary missions.All options begin with the International Space Station, a $100bn research complex flying 400km above Earth, the 286-page report released in Washington DC, said.One path includes Nasa's current plan to robotically capture an asteroid, redirect it into a high orbit around the moon and send astronauts there to explore. The report suggests that path continue with missions to the moons of Mars, then on to Martian orbit and finally to the surface of the planet.But two other paths would be less technologically daunting, NRC panel co-chair Jonathan Lunine of Cornell University told reporters during a webcast press conference.Technological riskNasa could follow the International Space Station programme, which currently costs the US about $3bn a year, with a series of lunar sorties, an outpost on the moon and then to Mars, the report said.The last path has the most stops en route to Mars, but poses the least technological risk since milestones have to be met along the way. That option would follow the space station with human missions to an orbit beyond the moon, then to an asteroid in its native orbit, then to the lunar surface, the moons of Mars, Martian orbit and then to Mars itself.Nasa said it supports the panel's findings."There is a consensus that our horizon goal should be a human mission to Mars," the agency said in a statement. "The pathways thrust of the report complements Nasa's ongoing approach."All options will depend heavily on international, private sector and other partnerships, according to the report titled Pathways to Exploration - Rationales and Approaches for a US Program of Human Space Exploration."We're really talking about international collaboration of a different scale than what has been conducted in the past," Lunine said.China co-operationIn particular, the United States' current relationship with China, which is not a member of the 15-nation space station partnership, needs to be reassessed, the report said."Given the rapid development of China's capabilities in space, it is in the best interests of the United States to be open to its inclusion in future international partnerships."The panel gave no specific estimate of what a Mars mission would cost. But based on past space initiatives, the public would support the endeavour."There is a temptation to rush to the question of dollars," panel co-chair and former Indiana Governor Mitch Daniels said. "Dollars is the secondary question."The pathways approach to Mars is "a very different way of doing business", Lunine said.