— The partners in the international space station say they are united in wanting to make maximum use of the orbiting facility in the next seven years but acknowledge different, possibly contradictory priorities will put stresses on station management once the space shuttle fleet is retired in 2010.

Meeting July 17 at the European Space Agency (ESA) headquarters here, the heads of the , Russian, Japanese, Canadian and European space agencies said each would try to win backing from their respective budget authorities to maximize use of the station, whose assembly is scheduled largely to be completed by early 2010. NASA has scheduled the retirement of the shuttle for that year, leaving the station’s crew – which is scheduled to increase from three to six in 2009 – with Russian spacecraft as their sole means of transport to and from the station for an undetermined period of time.

NASA Administrator Michael D. Griffin said the space agency would do its utmost to ease regulatory restrictions, contained in the Iran Non-Proliferation Act, on NASA’s purchase of Russian Soyuz capsules to maintain NASA’s role in the station after the shuttle is retired. also conceded that the U.S. Commercial Orbital Transportation Services (COTS) program, which is encouraging private industry to prode station cargo supply, could face delays that would force NASA to purchase ‘s Automated Transfer Vehicle, an unmanned cargo carrier; or ‘s H-2 Transfer Vehicle; or ‘s unmanned Progress cargo spacecraft.

The European vehicle has flown once; the Japanese vessel is scheduled to fly starting in late 2009. ‘s Progress is a veteran system but has smaller capacity than the European and Japanese vehicles. Beyond the mid-term logistical issues related to maintaining an operational facility with a crew of six astronauts and no shuttle, the partner nations also must figure out what they want to do next.

said NASA policy goes from the station to a lunar outpost and then to Mars. None of the other agencies seconded this scenario.

Anatoly Perminov, director- general of ‘s Roskosmos agency, said remains unclear about whether NASA will stay financially involved with the station beyond 2015. Depending on what NASA does, he said, will pursue plans to develop new infrastructure for the station, or invest in some other endeavor.

has three more small modules it is adding to the station between 2009 and 2011. “For other launches [of station hardware] between 2013 and 2015, it depends on how we agree, and whether the station will be operated beyond 2015. This has to be discussed.”

Perminov said hopes to have a clear idea by early 2009 about whether the partners agree to continue investing in the station or elect to focus on other space exploration programs in 2015.

reiterated that NASA is not fixed on a date for stopping its investment in the station. The day will come, said, “when sustaining the station costs more than the value of the research generated from it. But that will be a utility-driven decision, not a date-driven decision.”

ESA Director-General Jean- Jacques Dordain in recent months has made clear he does not want to hear talk of abandoning a facility that ESA has only just started to use. ‘s laboratory arrived at the station in February.

Dordain told the other station partners ESA would be asking its governments at a scheduled November conference to finance work to modify the Automated Transfer Vehicle to permit it to return payload from the station. As currently configured, the cargo vehicle is filled with garbage and burned up on a controlled re-entry into the Earth’s atmosphere.

SimonettaDiPippo, ESA’s director for human spaceflight and microgravity, said ESA has tentatively estimated that outfitting the vessel to return to Earth would cost about 250 million euros ($390 million) over three years.

ESA also is discussing with a possible collaboration on a future crew-transport system. But it is unclear whether this proposal will be ready for a final decision by ‘s governments in time for the November conference.

DiPippo said ESA also has not abandoned the idea of planning for a small orbital laboratory of its own in the event the international space station is abandoned.

DiPippo said NASA’s partners fully understand that the agency in the coming years will face increasing pressure to cut station-related costs as it pursues its lunar- and Mars-related exploration programs.

also is considering its exploration options but appears divided over whether a lunar-exploration effort should be undertaken instead of a program to prepare directly for a Mars sample return and eventual human presence there.