On my second space walk, I was riding the Canadarm, heading down toward the payload bay of the space shuttle, and I could see the space shuttle highlighted against the Earth in the background, and there was this black, infinite, hostile void of space. I remember looking down at the Earth and thinking, "Beneath me is a 4½-billion-year-old planet, upon which the entire history of the human species has taken place." That was an incredibly humbling moment, and I had a bit of an epiphany.

One of the things that's really exciting from my perspective is that Canada is one of the major spacefaring nations. The list of our achievements is profound and significant, and it's not just in robotics, it's also in the life-sciences research experiments that take place on board and other space-science experiments. I'd love to see Canada go from being a major spacefaring nation in low-Earth-orbit missions to those beyond, making sure we're part of those missions to Mars - not just from a technology perspective, but sending humans into beyond-Earth orbit.

When I was at McGill medical school, there was a writer, Ted Rosenthal, who used to write for the New York Times - tragically he died of leukemia at a very young age. He talked about how we can have an opportunity to live a lifetime in a moment, in a day, in a month, in a year - when you're confronted with the finite reality of your own existence, all these moments become lifetimes.

The first space walk, it's really got your attention. You know you're travelling eight times faster than a rifle bullet, and you're outside. Second space walk, you're a lot more relaxed, you're looking over your shoulder, admiring the view of Earth. What was funny about the third space walk was that mission control in Houston called and said, "Take a moment and enjoy the view".

On my second space walk, I was riding the Canadarm, heading down toward the payload bay of the space shuttle, and I could see the space shuttle highlighted against the Earth in the background, and there was this black, infinite, hostile void of space. I remember looking down at the Earth and thinking, "Beneath me is a 4½-billion-year-old planet, upon which the entire history of the human species has taken place." That was an incredibly humbling moment, and I had a bit of an epiphany.

What space brings to you is that global perspective, that planetary perspective, that we're all in this together, and no matter where you're living on Earth, we're all part of this amazing journey.

What an incredibly proud moment as a Canadian to have the Canadian flag on the left shoulder of your space suit, looking at the Canadian logos on the robotic arm in the payload bay of the space shuttle, and there's the Orbiter Boom Sensor System, which was an extension of the Canadarm to inspect the tiles underneath the orbiter. It struck me that there were more Canadian logos in space than any other country's I saw.