In an article for the New York Times he said: "I’ve no complaints. I’m very grateful for the experiences I’ve had on this planet.

"As an astronaut I spacewalked 220 miles above the Earth. Floating alongside the International Space Station, I watched hurricanes cartwheel across oceans, the Amazon snake its way to the sea through a brilliant green carpet of forest, and gigantic nighttime thunderstorms flash and flare for hundreds of miles along the Equator.

"From this God’s-eye-view, I saw how fragile and infinitely precious the Earth is. I’m hopeful for its future."