Unless Canada makes a lot more contributions to the International Space Station, it could be a while before another Canadian astronaut visits the giant orbiting space laboratory.

For the moment, what's clear is that no Canadians will be heading up to the space station before 2017 – at the earliest.

"We've kind of booked up the flights through the end of 2016," NASA's chief astronaut Bob Behnken said in an interview from Houston.

Story continues below advertisement

Right now, Canada is not even in a position to get a spot for one of its two active astronauts to take part in a mission.

Under a bartering system, it collects "credits" based on its contributions to the development of the space station, with the credits traded in for trips by astronauts.

But Mr. Behnken says Canada used up most of them for Chris Hadfield's five-month visit, which ended in May, 2013.

"They [Canadians] have another opportunity that's projected, but not out until the 2019-2020 time frame, just depending on how the balance of contributions works out." Mr. Behnken said.

"So if they wanted to fly more often, they unfortunately would have to contribute more to the space station."

When the Canadian Space Agency was contacted recently, it had nothing new to add to what CSA president Walt Natynczyk said in April about the next space trip by a Canadian.

"We're working with the international community or the partnership with the International Space Station to see when is the next opportunity that we can get one or both of our astronauts into space," Mr. Natynczyk said on April 20.

Story continues below advertisement

Right now, the only way for any international astronaut to get to the space station is by hitching a ride on a Russian Soyuz spacecraft.

But that could change as private U.S.-based companies continue to develop space capsules to ferry astronauts up to the space station.

Canada's two astronauts may even have a choice of their space bus when their turn finally comes.

"Our current plan is to continue to use the Soyuz until Boeing, Sierra Nevada or SpaceX – one of the three companies that we have on the U.S. side that are developing vehicles to visit the space station – are kind of ready to take us there instead," Mr. Behnken said.

"We don't yet have the contracts in place to specify what dates those vehicles would be out there, but it's in the 2017 time frame."