MOSCOW (Interfax) -- A question mark is hanging over the continuation of Lance Bass' training for a flight to the International Space Station (ISS) as a tourist in a Russian-European crew, experts say.

Bass is undergoing the full-fledged training needed for a short-term trip to the ISS later in the year, but no preliminary payments from him have been forthcoming, a source in the Gagarin Cosmonaut Training Center told Interfax on Tuesday.

"The whole affair looks like a promotional stunt," an expert in Star City outside Moscow said.

Sources in the agency told Interfax that Bass and the Russian Aerospace Agency signed a preliminary contract in July. He will not, however, get clearance for the flight until foreign companies sponsoring the project make their payments.

Earlier this year, Hollywood's Destiny Production movie company expressed readiness to take part in the project.

It plans to turn Bass' training and the entire mission into a large for-profit project.

Mir Corp., a company specializing in making a commercial enterprise of Russia's space activities, also supports the mission.