", Colonel Hadfield speaks about when he first flew in space, in a 1995 shuttle mission. The odds of dying in a shuttle launch at the time were about 1 in 38; he woke up that morning knowing that by the end of that day he would either be in space or dead.
Later, clad in his spacesuit and crawling into the spaceship on his hands and knees, he realised that the dream he had had when he was nine years old was now about to come true.
"You have taken the dreams of that nine-year-old boy, which were impossible and dauntingly scary, and figured out a way to reprogram your primal fear," he says. "That enabled me to come back with a set of experiences and a level of inspiration for other people that never could have been possible otherwise."
Colonel Hadfield has inspired thousands of children and adults, and his attitude to science education is optimistic. "Our level of worldwide scientific literacy has never been higher," he says. "When you look at the number of people who have access to education and access to the internet, it is tremendously enabling; anybody who has any curiosity can look up any fact they want to pursue. It really bodes well."
And, he adds, he will never forget his own inspiring teachers.
"Every single one of us is for ever indebted to the people who have taught us," he says. "Sometimes the lessons came in a formalised setting and sometimes not, but we are all in debt to the people who took the time to teach us the skills that we have.
"I very much feel that way towards all the teachers that have taught me. And I also think that if someone has taken the time to teach you something, you now have a debt and you really owe it to make sure that someone else gets an education as least as good as your own.
"It is the only way that we can have the quality of life that really enables people to succeed."
Questions that are out of this world
Chris Hadfield called on schoolchildren in the UK and Ireland to ask him questions on Twitter and Instagram, using the hashtag #personalrocketscientist
Oisin, aged 6, asked: "What does space smell like?"
Answer: "A bit like gunpowder or brimstone, like a witch has just been there."
Liam, aged 9, asked: "How did you have enough oxygen to stay in space so long?"
Answer: "The space station is sort of like a big metal bubble and slowly we use up the oxygen, so every ship that visits us brings a little bit more oxygen. That's how we stay alive in space."
Sam asked: "How many asteroids did you see from the ISS?"
Answer: "The Earth gets hit by 100 tonnes of meteorites a day but you don't see them very often. I only saw one, so even though asteroids are flashing by the space station all the time I only saw one in six months in space."
More questions and answers at personalrocketscientist.com