LONGUEUIL, Que. - Canada's landmark mission to the International Space Station could be the last visit by its astronauts to the orbiting laboratory for five years.

A Russian Soyuz space capsule blasted off on Wednesday from the Baikonur cosmodrome in Kazakhstan, carrying veteran Canadian astronaut Bob Thirsk and two crewmates.

But once Thirsk returns to Earth in November, it will be a while before a Canadian returns to space.

"It'll be five years from now," said Pierre Jean, Canada's space station program manager. "And the next one (after that) will be five years later."

The next "for-sure" flight to the space station by a Canadian will also be on board a Soyuz.

Jean says Canada's next space travellers should be its two newest recruits - Jeremy Hansen and David St-Jacques, who joined the Canadian astronaut corps earlier this month.

The 55-year-old Thirsk, Russian cosmonaut Roman Romanenko and Belgium's Frank De Winne, are due to arrive at the giant space station on Friday for a six-month stay.

The landmark mission will be Canada's first long-duration mission in space.

Thirsk's sojourn will also include a visit from fellow Canadian space traveller Julie Payette, whose 16-day mission starts June 13 aboard the space shuttle Endeavour.

In an interview just days before his space flight, Thirsk acknowleged he won't be the person who goes to the moon for Canada.

"But I do think that the work I'll be doing during the six-month expedition aboard the space station is pioneering work. I think that, in a sense, I'll be contributing and paving the way for newer astronauts to make that voyage."

Thirsk is one of Canada's longest-serving astronauts. He made his first space flight aboard the U.S. space shuttle Columbia in 1996.

The U.S. space shuttles are tentatively scheduled to stop flying in 2010 and if that happens, the only way up and down to the space lab will be with the Russian Soyuz spacecraft.

Jean said that if the mothballing of the American shuttles is extended, there's a chance Canadian astronaut Chris Hadfield will make his third space flight on one of them.

Hadfield was standing by in Kazakhstan to serve as Thirsk's backup in the event he fell ill.

Scores of reporters, dignitaries and relatives who watched Wednesday from a viewing stand about 1.5 kilometres away from the launchpad applauded as the rocket carrying the Soyuz roared into the sky.

Among them were Thirsk's three children and his 81-year-old mother Eva.

"He's doing what he's wants to do," she said. "And he's so happy about it. And I'm so happy for him."

Footage broadcast by NASA TV from inside the Soyuz showed the three astronauts waving and giving the thumbs-up.

Thirsk's brother-in-law Emmanuel Triassi got up early to watch the lift-off from the Canadian Space Agency in Longueuil, south of Montreal, on a giant screen.

The 57-year-old construction engineer says it was an emotional moment.

"I'm extremely excited, it's almost undescribable," he said, standing in front of a life-size cardboard cutout of Thirsk.

Retired Canadian astronaut Bjarni Tryggvason, who was also at the agency, admitted he was feeling a bit envious.

"I know Bob is just absolutely thrilled now," Tryggvason said in an interview.

"He's realized his second space flight. Now he's going to be up there for six months. I'm jealous as hell of him."

Three different space shuttles are scheduled to visit the station during Thirsk's mission, as well as three cargo vehicles - two from Russia and one from Japan.

As the permanent crew of six settles in and Payette and her space shuttle crew of six arrive in a couple of weeks, there will be 13 people aboard - a record number for the space station.

Thirsk, who was born in New Westminster, B.C., will also be celebrating his birthday in space on Aug. 17.

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