In Boldly Go: Reflections on a Life of Awe and Wonder (Atria, Oct.), Shatner recounts, among other experiences, his 2021 space flight.

You write that when you went to space, “there was no mystery, no majestic awe to behold... all I saw was death. I saw a cold, dark, black emptiness.” How surprised were you by that?

I was struck dumb. I was absolutely gobsmacked because I’ve been amazed by the miracles of space for a long time. And I saw none of that in that blackness. All I saw was what I described in that quote. And it came as a shock because I had just been looking at Earth as we were leaving it, and I was thinking, my God, look how beautiful it is.

How did you feel when you returned to Earth?

I couldn’t stop crying, and I wondered, what the hell’s the matter with me? I sat down in the cab of a truck and tried to think about what the weeping was saying. It took me time to realize that I was grieving for everything that’s been happening to the Earth. Millions of things, that took five billion years to evolve, are disappearing as you and I are talking, never to reappear. But then I went to thinking about the miracles of love and comfort and empathy and sympathy.

What do you think is the final frontier?

Amusing that you should ask that! I’ve been asked to give a talk to a group of surgeons, and I’ve entitled it “Space is not the Final Frontier.” And I’ll go on to say, “here’s a frontier, there’s another frontier here.” So the hook is that space is not the final frontier. And it isn’t. Apart from death, I don’t think that there is one.

With everything that you’ve accomplished, how do you feel about still being best known as Captain Kirk?

I’ve never felt badly about it. I mean, he was a leading man, masculine, fighting, getting the girl, going off on adventures. What could be more fun for an actor than to be doing that, until he gets into character roles? When I realized how important Star Trek had become to many people, it was clear that Captain Kirk left an impression. But then, people have come up to me to talk about the influence of my doing Rescue 911 and other programs. There are many things that I have done that were all brought about by the celebrity that was foisted on me by Captain Kirk. So I am in deep debt to him.