When the history of human space flight in the 20th century is finally, fully written, it will not be the triumphant lunar landing of Apollo 11 or the survival drama of Apollo 13, that emerges as the most significant of them all. It will be Apollo 8, the first lunar orbital mission — the moment human beings became a two-world species, wrenching ourselves away from the gravitational hold of Earth and sailing across the deep waters of deep space. That the mission occurred in 1968—the bloodiest year in modern history—and redeemed that year with the iconic Earthrise photo and the historic reading of Genesis from lunar orbit on Christmas Eve, was not part of its original objectives but was among its greatest achievements.

In the 1990s, I wrote the story o…