STAR CITY, Russia (AP) -- The next crew members of the International Space Station said Tuesday they were proud of their mission, which involves the U.S. space shuttle's return to flight.

The Discovery space shuttle is set to be launched and dock at the station in mid-May in the first mission since shuttle Columbia burned up on re-entry in February 2003, killing seven people. Since then, Russian spacecraft have been the only link to the international space station.

Russian cosmonaut Sergei Krikalev, NASA astronaut John Phillips and Italian Roberto Vittori of the European Space Agency are set to blast off to the station on board a Russian Soyuz ship on April 15.

Vittori is set to return to Earth in another Soyuz after a 10-day stint on the station together with the station's current crew, Russian Salizhan Sharipov and American Leroy Chiao. Krikalev and Phillips will stay on the station.

"It's a very important flight for NASA and for our international partnership, because we will be returning the shuttles to flight during our expedition," Phillips said.

He said Krikalev and he would be taking up pictures of Discovery during its approach, surveying it with long-lens cameras for any sign of damage on its surface - part of NASA's efforts to enhance the shuttle flights' safety.

"This can be a very tense moment for us, but it's the one I'm proud to take part in," Phillips said at a news conference in Star City, the cosmonauts' training center outside Moscow. "For me, having flown on the space shuttle and knowing what a wonderful vehicle it can be, it will be a really exciting moment."

NASA has devoted the past two years coming up with ways to keep foam insulation from coming off the fuel tank during liftoff, as it did on Columbia. But if a big piece did fall off and hit the shuttle, and the damage could not be fixed, Discovery's crew of seven would have to remain at the space station until another shuttle, Atlantis could be sent to the rescue.

Krikalev has warned recently that it would be difficult for the space station to accommodate seven extra people. He said Tuesday that the break in shuttle flights have led to the station being cluttered with excessive scientific equipment, leaving less space for the crew.

Krikalev voiced hope that the shuttles' return to flight would help to expand the station.

The station's crew is set to conduct several dozen scientific experiments, including medical and biological research, studies in plasma crystals and space navigation.

Roberto Vittori said his Eneide scientific program included studies on possible links between space radiation and earthquakes.

Just as the station's next crew was wrapping up its training, Russia's space agency reminded NASA that it would start charging money for U.S. astronaut rides on Soyuz ships starting next year. The agency has sent a letter to NASA asking it to quickly solve the issue, according to its spokesman, Vyacheslav Mikhailichenko.

Krikalev has spent nearly two years in orbit, over five missions dating back to 1988, making him one of the world's most experienced space travelers. Phillips flew a 2001 shuttle mission, while Vittori spent 10 days on the international space station in 2002.

Each had mascots to take along.

For Vittori, it's a toy rabbit given to him by his wife 18 years ago. "It has flown with me when I was a test pilot, it has been to space three years ago, and it will fly again in April," he said.

         Complete Coverage: ISS Expedition 11