BAIKONUR, Kazakhstan - Canadian astronaut Bob Thirsk is on his way to a six-month stint aboard the International Space Station.

A Russian Soyuz space capsule carrying Thirsk, Russian cosmonaut Roman Romanenko and Belgium's Frank De Winne soared into the hot afternoon skies over Kazakhstan's northern steppe Wednesday.

The landmark mission will both double the crew of the space station, and mark Canada's first long-duration mission in space.

The three will join the three crew members already on board the space station, giving the station six permanent members for the first time.

Scores of reporters, dignitaries and relatives watched from a viewing stand about 1.5 kilometres away, applauding as the rocket 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 for the camera.

Thirsk's brother-in-law Emmanuel Triassi watched the lift-off from the Canadian Space Agency, south of Montreal, on a giant screen.

He was among about 100 guests who included family and friends of the Canadian astronaut.

Triassi, a 57-year-old construction engineer, says it was an emotional moment.

"I'm extremely excited, it's almost undescribable," he said.

At age 55, Thirsk is one of Canada's longest serving astronauts. He made made his first 16-day space flight aboard the U.S. space shuttle Colombia in 1996.

His mission will include a visit from fellow Canadian space traveller Julie Payette, whose own 16-day mission will begin June 13 aboard the space shuttle Endeavour.

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.

In an interview last week, Thirsk acknowledged that most North Americans are more familiar with the space shuttle program than they are with the Soyuz, a staple of Russian space travel for nearly four decades.

"The Soyuz is an older technology," he said. "It's been around since the late '60s or early '70s and not a lot of refinements were made to it."

Still, the Soyuz has carried more people into space than any American vehicle, he added.

In addition, the U.S. space shuttle program is tentatively scheduled to end in 2010 and for at least four years after that, the Americans will rely entirely on the Soyuz for space-station missions.

Fellow Canadian astronaut Chris Hadfield was standing by in Kazakhstan to serve as Thirsk's back up in the event he fell ill.

The Soyuz will remain parked outside the space station until November when Thirsk will use it to return to Earth.

When he and his colleagues arrive, they will join three others who are already on the space station. And when Payette and her crew of six arrive, there will be a record 13 aboard.

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