On the morning John Glenn was about to ride a rocket into orbit, he looked at the IBM computers calculating his path around the Earth and said something no one expected.
“Get the girl to check the numbers.”
The girl was Katherine Johnson.
She was forty-three years old, a Black mathematician working in a segregated basement at NASA’s Langley Research Center in Virginia. She had spent her entire career being told she belonged in the back of the room, in the back of the bus, and in the back of history.
But on February 20, 1962, John Glenn refused to launch until she said the math was right.
Katherine Johnson was born Katherine Coleman on August 26, 1918, in White Sulphur Springs, West Virginia. She was a child prodigy who entered college at fifteen and graduated summa cum laude at eighteen. In 1939, she became one of the first three Black students allowed into the graduate program at West Virginia University. She joined NACA (NASA’s predecessor) in 1953, assigned to the West Area Computing unit — a segregated group of Black women who performed the complex calculations that powered the space race.
They were called “human computers.” They worked with pencils, slide rules, and mechanical adding machines because the electronic computers of the era were still unreliable and limited.
Katherine didn’t just calculate numbers. She understood them. She saw trajectories the way artists see light. When she moved to the Flight Research Division in 1958, male engineers told her trajectory briefings were “for men only.” She asked a simple question: “Is there a law against it?” There wasn’t. So she walked in and sat down.
In the days before Glenn’s flight, the brand-new IBM 7090 had run the orbital equations. But Glenn didn’t trust it. He had seen computers glitch before. This was not a drill. This was a man sitting on top of a rocket that would accelerate him to 17,500 miles per hour. One wrong decimal point in the re-entry angle and the capsule would either burn up or skip off the atmosphere into space forever.
So he made a direct request: Katherine Johnson must verify the numbers by hand.
She sat at her desk with a mechanical calculator and worked for a day and a half. She checked launch windows, orbital paths for three revolutions, re-entry angles, and every possible emergency return scenario. When she finished, her calculations matched the computer’s exactly.
She signed off.
Glenn read the report and gave the go-ahead.
On February 20, 1962, at 9:47 a.m., Friendship 7 lifted off. Glenn became the first American to orbit the Earth. During the flight, the capsule’s automatic control system failed. He had to fly manually using the emergency procedures Katherine had helped verify. He splashed down safely 800 miles southeast of Bermuda after nearly five hours in space.
That single verification was only one chapter.
Katherine Johnson calculated the trajectory for Alan Shepard’s first American spaceflight in 1961. She helped solve the complex rendezvous equations for Apollo 11 in 1969 — the math that determined whether Neil Armstrong and Buzz Aldrin could return from the Moon. She contributed to the Space Shuttle program and early concepts for Mars missions.
She worked at NASA for thirty-three years, retiring in 1986.
For most of that time, almost no one outside the agency knew her name.
Then, in 2015, President Barack Obama awarded her the Presidential Medal of Freedom. In 2016, she was portrayed by Taraji P. Henson in the film Hidden Figures. In 2017, NASA named a computational research facility after her. In 2019, at age 101, she received the Congressional Gold Medal.
She passed away on February 24, 2020, at 101 years old.
John Glenn had died three years earlier.
When asked late in life what she was most proud of, she didn’t mention the Moon, the missions, or the awards. She said something simpler:
“I loved the work. I loved the stars and the story we were part of. It was a joy to contribute to what would be written.”
That is what she was doing in February 1962 — sitting at a mechanical calculator in Hampton, Virginia, working for a day and a half while a man’s life depended on her numbers. She was helping write the story of space. She was speaking the only language she needed: mathematics — the language that governs objects moving through the vast, unforgiving geometry beyond Earth.
A man didn’t trust a machine. He trusted a person.
The person was right.
The rocket flew.
