Although Russia and the United States agreed to split the costs of sending men and material to the space station, only Russian spacecraft have been used since last year's space shuttle disaster; space officials say that by carrying the sole burden, Russia has fulfilled its end of the agreement.
"If the Americans want to fly Soyuz (spacecraft) in 2005, they will have to compensate us the costs," space agency head Anatoly Perminov said, according to the ITAR-Tass news agency.
NASA aims to resume shuttle flights next spring, but efforts to enhance their safety may cause delays.
The European Space Agency is also working on a cargo ship to supplement the U.S. and Russian vessels that fly to the space station.
To prepare for its arrival more than a year from now, station crewmen Gennady Padalka of Russia and Mike Fincke of the U.S. replaced outdated laser reflectors with newer models Tuesday. The six old reflectors were built in the late 1990s and have been in orbit since 2000, and the new ones will make it easier for the unmanned ships to close in and pull up, NASA officials said.
The European cargo ship will supplement the U.S. and Russian vessels that fly to the space station. The grounding of NASA's shuttles following the highlighted the need for a more diversified fleet.