I had never heard of a cavitating venturi valve until Neil Armstrong told me about it. A few years ago, when I was preparing to teach a space history course for NASA engineers, I asked Armstrong to name the engineering contributions to Apollo he most admired. The little valve with the obscure name was at the top of his list. After a bit of digging and a long conversation with a rocket propulsion expert, I came to understand why. Two of those valves, devised by engineers at TRW, were deep within the machinery of the lunar module’s descent engine. They allowed the proportions of fuel and oxidizer entering the combustion chamber to be regulated so precisely that the lunar module could vary its thrust, even hover, without busting its stringent fuel budget. The fact that Armstrong remembered those valves decades later was typical. He had always been driven by a desire to understand the machines he flew; at his core was the essence of the engineering test pilot. And after all, those little valves had allowed him to guide his lunar module Eagle to the first landing on the alien ground of another world.

That landing, and the “one small step” that followed, changed our world forever. But it didn’t change Neil Armstrong. When I sat down with him in 1988 to talk about Apollo 11, he told me his satisfactions came not from having made history’s first lunar landing, but from the many small technical advances he had helped to achieve over the course of his career. “They’re very little things,” he said, like figuring out how to do a quick and easy check of the lunar module’s navigation system by sighting on the sun shortly before beginning the powered descent to the Moon. Or, early in the descent burn, checking the accuracy of the craft’s trajectory by tracking landmarks on the surface. (And there was one not-so-little thing he didn’t mention: helping to develop the Lunar Landing Research Vehicle that allowed him to realistically simulate flying in the Moon’s one-sixth gravity. It was a singularly unforgiving machine to fly, and in 1968 it almost cost Armstrong his life — but he insisted it was essential preparation for a flying task unlike any other.)

“You take great joy,” Armstrong told me, “out of the time when you come up with some new gimmick or procedure or gadget or approach that allows you to get a little further than you ever were before. Get to a new plateau to look from.”

There is a painting by Georgia O’Keefe called “Ladder to the Moon”; I first saw it in the office of Caltech geologist Lee Silver, who helped train the Apollo astronauts to explore the Moon. In it, a wooden ladder hangs in midair above the New Mexico desert, not quite reaching the first quarter Moon. Silver pointed out that it’s up to us to extend it with the power of our imaginations.

Neil Armstrong never saw himself as anything other than one of the 400,000 people — mostly anonymous — who helped make the ladder reach all the way. His humility, his self-deprecating sense of humor and his appreciation of history were some of the qualities we cherished in him. But he was also a supremely competent professional who brought his extraordinary intelligence to bear on making an impossible dream come true. We won’t be able to look at the Moon now without thinking of him. And we wouldn’t want to.

Andrew Chaikin is a science journalist, space historian and the author of several books on space, including “A Man on the Moon: The Voyages of the Apollo Astronauts.”

Andrew Chaikin is a science journalist, space historian and the author of several books on space, including “A Man on the Moon: The Voyages of the Apollo Astronauts.”