I’ve always been a musician. I think we all are, it’s just that only some of us learn to play instruments.

I grew up with music; it’s how I meditated, how I learned about life.

With the jobs I’ve been in—military pilot, engineer, astronaut—I’ve lost many friends and colleagues. But the first, and the toughest, was Captain Tristan de Koninck. We were both CF-18 pilots, defending Canada during the Cold War, scrambling out to inter- cept Soviet bombers practicing dry-run attacks on North America. We were in our late twenties, we’d both been through military college and got married; he had two girls and Helene and I had two boys. We flew together, we were going to be lifelong friends. He was a very good guy, physically fit, and a great pilot; a better pilot than I.

Then in May 1986, after an air show on Prince Edward Island, Tristan crashed his CF-18. He had taken off, pulled up hard into low-lying clouds, then flown straight down into Malpeque Bay at 700 miles an hour. Nobody knew why. Maybe he got disoriented as he pulled up, or maybe it was a technical malfunction. Either way, it was a horrible, horribly short end to a vibrant life.

I was flying down in Bermuda when I got the news. His wife, Sue, asked if I would come back and speak at his memorial. Of course I said yes, and in no time I was in my CF-18 on the 1,000-mile flight back to CFB Bagotville. It was a very sombre flight home, trying to digest what all this meant. He had a lot of plans. We had a lot of plans.

As soon as I landed I went to see Sue, who gave me Tristan’s twelve-string guitar and said, “I’d really love it if you could play a song with this.” I had a six-string, and she’d put up with so many evenings of us jamming together in their living room over the years.

Again I said yes, but this time I didn’t know if I was up to it. I was angry, at the vehicle for killing him and the sheer injustice of the accident. And sad. But I took the twelve-string back to my place and started going through our songbook. And the song that made sense was “This Old Guitar” by John Denver.

We’d had played it together, harmonizing our voices, so many times. I had always loved the lyrics, but now they packed an extra punch: Denver sang that his guitar taught him to sing love songs, how to laugh and to cry; it brightened his days and was his friend on cold, lonely nights.

The problem was, once I sat down to practice the song, I didn’t make it through once. I probably tried two hundred times, but it was just too raw; it brought the memory of him too cruelly alive. I couldn’t reconcile that with the fact I’d never see him again.

Then the moment of the memorial came. There was a big picture of Tristan, and his wife and all our friends were there. I went up and played the song.

I made it through, mostly by imagining Tristan was playing beside me. Music gave me a way to deal with the most harrowing thing I had yet faced in my life, a way to say the kind of things I would have said if I’d known how, instead of keeping them bottled up inside.

That was thirty-three years ago. When I play or hear “This Old Guitar” today I’m exactly there, in Tristan’s living room, or at the memorial. That song is both a moment in time and a treasured thing that keeps my friend alive in my mind. It allows me to invite Tristan over to play.

People often ask me, “Do you miss walking in space?” It seems like an odd question; that’s just one thing of so many I’ve done, and I usually say, no, I don’t miss it. What I do miss are people, and one of the people I miss the most is Tristan. I wish he was here, beside me in our late fifties, to enjoy life with me.

That’s a big part of music. It can help remind you of a person or a time or a place that meant a lot to you. “This Old Guitar” is not one of John Denver’s biggest songs, but when I play it, I’m much more liable to smile than to cry.

Chris Hadfield is a retired engineer, military pilot, and astronaut. During three space flights he was the first Canadian to walk in space and the first to command a spaceship. Hadfield is an author and professor, and his cover of the David Bowie song “Space Oddity,” the first music video ever recorded in space, has had more than forty million views on YouTube.