The Kinsman Saga by Ben Bova

Hero or Killer?

In a startling future that's coming closer every year, Chet Kinsman is an astronaut ace who has done everything in space--including committying the first murder. It's a secret he can never escape, not even on the Moon, where he's head of the first U.S. lunar colony.

But suddenly, a series of shocking yet strangely inevitable circumstances forces Kinsman to confront his hidden past and decide Earth's destiny. In a desperate countdown to nuclear annihilation, Kinsman struggles against a deadly paradox: if he rescues the world, he may end up destroying himself.