Seated in Mission Control, Chris Kraft neared the end of a tedious Friday afternoon as he monitored a seemingly interminable ground test of the Apollo 1 spacecraft. It was January 1967, and communications between frustrated astronauts inside the capsule on its Florida launch pad and the test conductors in Houston sputtered periodically through his headset. His mind drifted.

Sudden shouts snapped him to attention. In frantic calls coming from the Apollo cockpit, fear had replaced frustration. Amid the cacophony, Kraft heard the Apollo program’s most capable astronaut, Gus Grissom, exclaim a single word...

By the summer of 1968, a sense of deep unease had engulfed the American republic. Early in the year, the Tet Offensive smashed any lingering illusions of a quick victory in the increasingly bloody Vietnam conflict. Race relations boiled over in April when a single rifle bullet took the life of Martin Luther King, Jr. Two months later, as Bobby Kennedy walked through a hotel kitchen, he was shot in the head. The red, white, and blue threads that had bound America for nearly two centuries were faded and fraying.

Amid this national turmoil, senior planners at the country's space agency were also having a difficult year. Late that summer they quietly faced their most consequential decision to date. If NASA was going to meet the challenge laid out by President John F. Kennedy, its astronauts would soon have to take an unprecedented leap by leaving low-Earth orbit and entering the gravity well of another world — the Moon. Should they do it?

A vast, gray expanse loomed just a few hundred meters below as Neil Armstrong peered out his tiny window. From inside the spidery lunar lander, a fragile cocoon with walls only about as thick as construction paper, the Apollo 11 commander finally had a clear view of where the on-board computer had directed him to land.

He did not like what he saw there. A big crater. Boulders strewn all around. A death trap...

As inevitably happens in August, a sweltering heat with the tactility of dog's breath had come over Houston when Raja Chari reported to the Johnson Space Center. Just shy of his 40th birthday, the decorated combat veteran and test pilot had been born too late to see humans walking on the Moon. No matter, he was in awe of the new office...

As Apollo 13 astronaut Fred Haise floated in the tunnel snaking between the Lunar Module and Command Module, he heard — and felt — a loud bang. Around him, the two vehicles began to contort. Then, the metal walls of the tunnel crinkled as the spacecraft shuddered...

And then it was all over.

After the drama of Apollo 13, the final four human missions to the Moon in 1971 and 1972 flew smoothly. With each successive, increasingly routine landing, astronauts made longer forays out onto the dusty lunar terrain and delved deeper into the scientific secrets hidden there...