When your job involves flying rocket ships that blow up on a regular basis, the answer is plenty.

On his first shuttle mission in 1995 the Canadian astronaut's odds of death were one in 38. As the pilot of the Soyuz rocket in 2012 he knew he had a four-second window between system failure and death.

But back on Earth, as Hadfield sits in Sydney Observatory's east dome, it's clear he's still in survival mode, assessing every variable.

"Imagine if we were locked inside this observatory, just us and a camera crew for the next six months, and our little group had to deal with anything that might come up," he says.

"If you got appendicitis I would have to take your appendix out. If one of us goes blind, if the power goes off, no matter what happens our little group of people have to be able to solve the problems."

The situation does not need to be as dire as life or death for his training to kick in. It could be the risks of speaking to a reporter, or preparing for his sold-out show at the State Theatre in Sydney on Tuesday night.

"I always look everywhere and think: what is the next imminent threat? If there's not, you sort of relax. That's what astronauts are trained to do."

After more than 20 years as an astronaut Hadfield says the most common question he gets asked when back on Earth is how he goes to the toilet in space.

Hadfield decided he would become an astronaut after watching the Apollo 11 moon landing when he was nine years old and living on his family's farm in Ontario. The fact that Canada had no space program at the time was a minor detail.

"I started moulding himself into what I thought an astronaut ought to be," he said.

Hadfield studied engineering before becoming a fighter pilot and test pilot in the Royal Canadian Air Force.

He learnt several languages, including Russian to be able to communicate with the Russian cosmonauts, and in 1992 when Canada's new space program posted a "wanted, astronauts" job advertisement in the local papers, Hadfield was one of just four successful candidates. There were 5330 applicants.

So it seemed fitting that Hadfield should visit Australia, a country with no space program, as the world stands on the precipice of the next stage of space exploration: the search for extraterrestrial life.

"In history we are just at the point where we are starting to explore the third dimension and it's wonderful to be a part of that," he says.

"[But] right now if you're an Australian and you're interested in space travel you have to leave this country.

"What an awful situation within Australia, because either the kids that are really bright and motivated leave Australia, which is bad for the country and the economy, or they never pursue their potential and they stay, which is a stagnation that is incredibly destructive."

He acknowledges that many, now more than ever, question whether spending billions on space exploration is the wisest investment.

"[But] to me you have to, within the balance of society, you have to spend a preponderance of the money on the problems of today, but you have to spend some of it on exploring and on motivating things that are barely possible, and the real question is where do you draw your balance," he says.

Hadfield has embarked on three space missions, two spacewalks and a five-month stint on the International Space Station, including three months as commander.

And he has become as adept at social media as he was behind the Soyuz controls.

In fact, the Canadian astronaut has been credited with reinvigorating the public's interest in space travel.

Unlike Neil Armstrong, who became a recluse after images of his first steps on the moon were beamed into millions of homes around the world, Hadfield goes out of his way to share his life in microgravity with millions via his YouTube videos, Twitter and other online forums.

His cover of David Bowie's Space Oddity, recorded aboard the ISS, has been watched more than 26 million times.

He delighted fans when he had a Twitter conversation with Star Trek actors Leonard Nimoy and William Shatner, and his 2013 Reddit AMA was one of the most read threads to date on YouTube.

"I've seen thousands of sunrises that I wouldn't have if I hadn't flown in space … It's like someone is pouring a liquid rainbow on the edge of the world as it explodes into life and it happens every 92 minutes and it's gorgeous.

"It would be hugely selfish of me not to describe it and show people and not let them see the world for what it truly is."

Quick facts

• Three space flights
• Two space walks
• Orbited the Earth 2600 times
• 4,000 hours in space

Chris Hadfield is appearing at the State Theatre on Tuesday night in conversation with Ray Martin.