When Gordon Barnes joined the U.S. Air Force in 1956, he worked as a navigator on the tanker planes that refuel long-range bombers in midair. Coordinating a connection between two planes moving hundreds of miles an hour at 30,000 feet may sound exciting, but Barnes found the work routine. “It actually did get boring to me,” he says.

A few years later, he stumbled into a line of work he liked much better. The Air Force sent him back to school to get a master’s degree in geodesy—the science of defining the Earth’s size and shape and the fluctuations in its gravitational field.

At first, Barnes barely knew what geodesy was. But it grew on him. “It stimulated my mind like