If you've watched Apollo 11's moon landing, you know Charlie Duke's voice. Officially known as General Charles Moss Duke, Jr., he was the southern drawl from mission control on the other end of Neil Armstrong's famous landing speech.

Duke, now 80, turns out to be about what you imagine from someone named Charlie Duke. He’s from Charlotte, North Carolina, an Eagle Scout, and an accomplished Air Force test pilot. He's walked on the Moon. And he knows that when you venture beyond the atmosphere, all the preparation on Earth can't make you ready for everything you'll face.

Three years after Duke met Armstrong's "The eagle has landed” with “Roger, twang—tranquility," he found himself on the other end of the radio, as the lunar module pilot on Apollo 16. And he faced a very different, unexpected challenge—one no astronaut had trained for.

On the second day of the 1972 11-day trip to the moon and back, command module pilot Ken Mattingly lost his wedding ring. “It just floated off somewhere, and none of us could find it,” Duke says. Mattingly, perhaps worried his wife would accuse him of some extraterrestrial impropriety, spent his free moments desperately searching for the ring.

Astronauts may be the most prepared humans doing anything, anywhere. They know the components and mechanics of their ships inside and out. They train for years. They develop and incessantly practice protocols and procedures for endless worst-case scenarios. But for all their contingency planning, for all their years of practice drills, they hadn’t prepared for this.

By the next day, they still hadn't found the ring. They orbited around the moon for a day and still, it eluded them. They landed on the moon and Charlie Duke and Commander John Young got out. “So Young and I spent three days on the moon, came back and rendezvoused," Duke says. "It's now the eighth day of the mission, and Mattingly is still looking for his ring.”

They started their journey home that day. Three of the nation’s most brilliant scientists, hurtling through space, defeated in their quest to locate a small, sentimentally important gold band.

On the ninth day, the team went out for a space walk. The hatch was open, and Mattingly was floating alongside the ship, tending to a biological experiment anchored on a 10-foot pole. Duke suited up and floated out to check on him.

“It was spectacular out there,” he says. “The moon was over my left shoulder about 50,000 miles away and it was huge. To the lower right was the earth, just a thin sliver of blue and white, and I was mesmerized.”

As he turned to head back in, something caught his eye, small, glistening in the sun, floating slowly out of the door. He reached his big gloved hand out to catch the ring and missed. “Well,” he thought, “lost in space.”

Duke, Mattingly, the ship, and the ring were flying through space together at 3,000 feet per second, but in the absence of wind resistance, as Duke puts it, things just “move along together.” So there they were, floating while really zooming along—Charlie watching the unrushed ring head to its fate in the vast darkness.

But as he watched, Duke realized the ring was headed right for the back of Mattingly’s head. The astronaut, unaware, was absorbed in his experiment when the ring hit him right on the back of the helmet, turned 180 degrees, and headed back for the hatch. About three minutes later, Charlie caught it in his big gloved hand.

This is still a common occurrence on spacecraft where the lack of gravity means things don’t simply stay put. It's a seemingly uncomplicated issue, but is today as intractable for NASA as it was for Mattingly in 1972. At least his ring came back.

It’s tempting to attribute the ring’s return to the power of love or fate or some higher power yet undiscovered. Maybe Charlie Duke would cast his vote for the laws of physics. Or maybe not. He did become a devout Christian upon return to Earth.

Whatever the case, there's consolation here: If not even the astronauts can truly plan anything, neither can we. As Duke put it, “you plan and plan and plan but the unexpected always jumps up and bites you”—or slowly floats right into your hand.