NASA's space shuttles have been an integral part of Canada's space program, and how Canadian astronauts will get into space after they retire is still up in the air.
"For Canada, our flight heritage rests with the shuttle," said former Canadian astronaut Steve MacLean, president of the Canadian Space Agency.
He has flown on Atlantis, the shuttle set to blast off on its final flight at 11:26 a.m. ET Friday.
Speaking to the media from Kennedy Space Centre in Florida on Thursday, the eve of the final launch of NASA's space shuttle program, Maclean said the space shuttles carried 14 Canadians on 14 separate space missions over the past 25 years.
The space shuttles also allowed Canadian scientists to conduct experiments in space and Canadian engineers to contribute to space safety and technology through the use of the Canadarm robots attached to each shuttle.
The end of the program will definitely affect Canada, MacLean acknowledged.
"I think what's going to change the most is our human access [to space] in Canada is going to be reduced," he said. But he noted that other nations will have the same problem.
Only 1 Canadian astronaut flight scheduled
So far, MacLean said, Canada has only one scheduled space flight after the end of the space shuttle program. Col. Chris Hadfield will head to the International Space Station aboard a Russian Soyuz spacecraft in 2012 and return in 2013 after serving as the space station's first Canadian commander.
The Canadian Space Agency is in the process of negotiating future flights, MacLean said.
It is also involved in discussions with NASA, Europe and Russia about the future of human space travel.
"With the termination of the shuttle, we are at a crossroads. There are some decisions to be made about where the world goes next with respect to space," he said. "This is a series of negotiations that Canada will be part of."
In the near future, Canada will likely depend on Russia to bring people, and Europe and Japan to bring equipment to the International Space Station, Maclean said. That may change the frequency of space flights by Canadian astronauts, he added.
But he said things could be different in four or five years, when NASA is expected to have built a new space vehicle.
NASA is also planning to change its focus to services provided in orbit and rely increasingly on the commercial sector to take humans and cargo into orbit.
"I think that provides an opportunity for Canadian industry to participate," MacLean said.
On Friday, MacLean was set to watch Atlantis's final launch, along with Industry Minister Christian Paradis and Gary Goodyear, Minister of State for Science and Technology.
He said he felt nostalgic when he saw the shuttle on the launch pad.
"I think that's the mood that's here today — it's one of celebrating these last moments of an amazing program."