are the humans that go into space "heroes"

[Middle-aged Europe]

Yes, they risked their lives almost purely for the advancement of science and mankind.

And for trying to prove the technological and scientific superiority of the United States' system over the Communist system during the Cold War, which was at least 50% of the effort.

Not sure I'd call them heroes, since I define term as "someone who saves or helps other people" and that is what astronauts usually don't do. But they certainly were brave men.