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

What's clear for now is that no Canadians will be heading up to the space station before 2017 — at the earliest.

Bob Behnken, the chief of NASA's astronaut office in Houston, says our astronauts will have to wait their turn because all flights have been booked through to the end of 2016.

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The Canadian Space Agency's current astronauts are Jeremy Hansen, left, and David St-Jacques. They have completed their training, which began in 2009, but have never flown in space. (Sean Kilpatrick/Canadian Press)

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

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

He says Canadian astronauts will have another opportunity to visit the space station — but not until the 2019-2020 time frame.

Back in April, Canadian Space Agency head Walt Natynczyk said he was working on the next opportunity to get one or both of our astronauts into space.

When the space agency was contacted recently, it had nothing new to add to those comments.