“If she says they’re good,” Johnson recalled the astronaut saying, “then I’m ready to go.” That is how Katherine Johnson remembered John Glenn’s request, decades later.

The “she” was Johnson herself. The numbers were the flight path for the mission that would make Glenn the first American to circle the planet.

What strikes me about that line is what it quietly asserts. A man about to be strapped to a rocket trusted a person with a mechanical calculator to verify a room-sized electronic computer. And the person he trusted was a Black woman who had begun her Langley career in a segregated computing unit.

The flight path for Glenn’s Friendship 7 flight was worked out through NASA’s new network of IBM computers. They were fast for their day, and new enough that people didn’t yet fully trust them.

As author Margot Lee Shetterly put it in NASA’s official biography of Johnson, the astronauts were “wary of putting their lives in the care of the electronic calculating machines, which were prone to hiccups and blackouts.” Of course, that is her read of the mood, not a survey, so I’d take it as the reported feeling rather than gospel.

Glenn’s fix was blunt. In the days before launch, according to Shetterly, he asked engineers to “get the girl,” meaning Johnson, to run the same numbers through the same equations by hand. The same phrasing turns up in her Associated Press obituary, where a computer-skeptical Glenn is said to have insisted, “Get the girl to check the numbers.” 

The gist is consistent across the sources: he wanted a person to verify the result.

Who the girl actually was

Calling Katherine Johnson “the girl” undersells her by a wide margin. She worked at Langley for 33 years, retiring in 1986.

She understood the math of orbits well enough to reproduce the computer’s work herself. In 1960 she coauthored a report with Ted Skopinski, the first time a woman in the Flight Research Division got author credit.

Johnson described the job without false modesty. “Our office computed all the (rocket) trajectories,” she told The Virginian-Pilot in 2012. “You tell me when and where you want it to come down, and I will tell you where and when and how to launch it.” That is the confidence of someone who knows the math is hers, not the machine’s.

A day and a half of tiny digits

The check itself was not glamorous. Johnson sat down at her desktop calculating machine and worked the same equations the electronic computers had run, step by step. Shetterly wrote that it took “a day and a half of watching the tiny digits pile up: eye-numbing, disorienting work.” Take that as her description from the book, not a stopwatch reading.

The numbers matched. Glenn flew. On February 20, 1962, Friendship 7 circled Earth three times in 4 hours, 55 minutes and 23 seconds before splashing down in the ocean.

The mission is remembered as a triumph of rockets and engineering, which it was. It was also, in a small and human way, a triumph of one person’s arithmetic being used to verify the electronic system NASA was relying on.

What the moment quietly tells us

I keep coming back to the logic of Glenn’s request. The computer was faster. Nobody disputed that. What it lacked, that week, was a track record a person was willing to bet his life on. So the electronic computer system got checked by a woman with a mechanical calculator, and her yes was the one Glenn wanted. Speed is not the same as confidence, and confidence tends to attach to people before it attaches to tools.

Johnson’s later career reads like a list of everything that came after that day. She worked on Apollo and the Space Shuttle, and in 2015, at 97, President Obama gave her the Presidential Medal of Freedom. She died in 2020 at 101. For most of those years, almost nobody outside the flight-research offices knew her name, until Shetterly’s book and the film pulled her into public view.