Astronaut Dave Williams retired from active duty Saturday, ending an illustrious 16-year career that included two space shuttle missions and the record for longest total spacewalks by a Canadian, the Canadian Space Agency announced.

Retiring Canadian astronaut Dave Williams, right, and astronaut Rick Mastracchio are shown on the space shuttle Endeavour in 2007.
(NASA/Canadian Press/Associated Press)

The Saskatoon-born emergency medicine specialist, who was first selected as an astronaut by the Canadian Space Agency in 1992, spent a total of 28 days, 15 hours in space during his missions.

His first flight was in 1998 aboard the space shuttle Columbia. He spent 16 days on experiments focusing on the effect of weightlessness on the brain. He acted as scientist and subject in 26 experiments.

Williams completed his second space flight as a mission specialist in August 2007 to assist in construction of the International Space Station. During the mission, he established a Canadian record of 17 hours and 47 minutes in three spacewalks.

"I was seven years old when I dreamed of becoming an astronaut and I never thought it was going to be possible," Williams said in an interview late Friday with the Canadian Press following the space agency's announcement.

Jim Prentice, federal minister responsible for the space agency, said Williams's accomplishments in the past decade helped position Canada as a space-faring nation.

Williams inspired "young people across our country to take their place as members of Canada's next space generation," Prentice said in a statement.

His retirement leaves just three active Canadian astronauts: Julie Payette, Chris Hadfield and Robert Thirsk.

Speaking from Houston, Texas, Williams said it wasn't hard for him to recall his best moment in space. That was during his last flight.

"I was riding on the end of the Canadian arm, with the Canadian flag on my shoulder," said Williams, who also worked for NASA as director of the space and sciences directorate.  

Eyes on 'next generation'

He said he thinks it's an exciting time for the space program and he'd love to see a Canadian on the moon and beyond.

"Somewhere out there in Canada right now could be the next generation of astronaut that could be participating in missions to the moon," he said.

"Somewhere out there in Canada right now there might be a seven-year-old that might be participating in those first missions to Mars."

Williams's departure comes as NASA enters the final phase of the shuttle program. NASA plans about a dozen more flights, with the final mission due in 2010.

As honoured as he is to have been part of the program, he acknowledged that the "magnitude of the commitment" and time away from family for training and missions was tough.

"It was a great opportunity," he said. "My family was very, very supportive and I just really enjoyed being able to fly. But in many cases, when we're out in space — wouldn't it be great to be able to share this experience with our families firsthand?"

Williams and his family will be moving to Ontario where he will be exploring "various career options," the Canadian space agency said.

With files from the Canadian Press