PARIS — With assembly of the international space station nearing completion, the major investors – the United States, Russia, the European Space Agency (ESA), Japan and Canada – are discussing ways to ensure that neither the U.S. Vision for Space Exploration nor the ostensible 15-year design life of some early station hardware forces an early retirement of the multibillion-dollar facility.

At a meeting of the station partners here this week, a big topic was the engineering and financial measures that will need to be taken to keep the station operating until around 2020 and perhaps beyond.

NASA officials in recent months have sought to reassure their partners that the end of operations of the space shuttle in 2010, and the increasing budget focus of NASA on lunar and Mars exploration, will not cause the United States to withdraw from the station and leave the partners with the costs of operating the facility.

The station partners began meeting here July 10-11 as part of what is known as a Multilateral Coordination Board, where agency officials with first-hand knowledge of the station hash out issues. The heads of the participating agencies then are scheduled to meet at ESA headquarters here July 17 to discuss station operations, the transition to full-time station crews of six astronauts, compared to three at present, and the longevity of the facility.

Station partners spoke here July 10 as part of a symposium organized by the International Astronautical Federation celebrating 10 years of station operations.

Alexey B. Krasnov, head of piloted programs at ‘s Roskosmos space agency, said the design life of the FGB Zarya module, the first element of the station, is 15 years. Zarya was launched in November 1998, which in theory would mean de orbiting it in 2013.

But Krasnov said here July 10 that ‘s Mir space station, which was operated in the 1980s and 1990s, was designed to function for five years and ended up lasting 15 years. Roskosmos has similar hopes for the Zarya module and its other hardware on the international space station, Krasnov said.

Krasnov noted that intends to add electrical-supply and other hardware to the station beyond 2010 and is intent on using the facility for many years to come.

ESA and the Japan Aerospace Exploration Agency (JAXA), whose habitable station modules have only been launched in recent months, have said they are focusing their full attention on maximizing their use of the station.

“Some may say it is too soon, but we want to start discussing the extension of the life of the station,” said SimonettaDiPippo, head of human spaceflight programs at ESA. “And as part of a general exploration strategy we need to see how to enlarge the number of potential partners” in future space station use.

NASA Administrator Michael Griffin, in in early June to discuss space policy, said he could not imagine the United States walking away from the station before some date beyond 2016.

Yoshiyuki Hasegawa, JAXA’s ISS program manager, said Japan’s goal is to complete the installation of its Kibo module, whose habitable laboratory element has just arrived at the station, and then to ensure “stable operations for some time to come.”

Martin Zell, head of research operations at ESA’s directorate of human spaceflight, microgravity and exploration, gave a summary of each partner’s research projects at the station and said the research agenda is “a little light” because of policy favoring experiments tied to the Vision for Space Exploration.

But Jeff Bingham, senior advisor to Republican staff of the U.S. Senate Commerce, Science and Transportation Committee, said the U.S. Congress is intent on making sure that NASA’s Moon and Mars programs do not force a premature drawdown of resources devoted to the space station.

Bingham said the U.S. National Laboratory Initiative, which makes the U.S. segment of the space station – and those other segments allocated for U.S. use – a national laboratory, is one way of signaling congressional support for extending the station’s service life.

“Congress is saying that NASA should be preparing to use [the station] at least to Bingham said. “It’s an important statement: We have 20/20 vision when it comes to the station. Some of you may have been hoping you would get back that U.S.-allocated portion of your facilities because NASA doesn’t want to use it. But we are intent on ensuring that this investment we have made is used to the maximum.”