In a 1988 interview with The New York Times, he voiced disapproval of proposals to send humans to Mars, saying: "It's just as wrong as can be. It's wrong because it guarantees there won't be any space science. We know how NASA treats science as a second-class citizen when it competes with man-in-space programs."
I'm inclined to believe that.
But I must say, when I saw the headline about a 90-year-old "Explorer of Mars," an idea that occurred to me was having a one-way mission, sending some quite old persons to Mars, with no way to bring them back. I was assuming he'd be in favor of sending a man to Mars and imagined him saying I'm 90, send me! I'm going to die pretty soon anyway. I'd like to have a shot at making it to Mars. And you can just leave me there!
Would it be wrong to have a mission like that? Why is it that young people take the most risks with their lives? Shouldn't the oldest people take the most daring risks, since they've lived the greater part of their lives and therefore risk less of it?
But Horowitz what not that kind of Mars explorer, not the physical adventurer, but a man who did his explorations intellectually.