February 1962: John Glenn is strapped into Friendship 7, about to become the first American to orbit the Earth, and he refuses to launch. NASA's brand-new IBM computers have produced his trajectory, but Glenn does not trust the black box. "Get the girl to check the numbers," he says. "If she says they are good, I'm ready to go." The girl was Katherine Johnson, and it took her a day and a half of nonstop hand calculation to verify what the machine spat out in minutes. This episode traces how a Black woman from the segregated South became the ultimate safety net for the American space race.

Born in 1918 in White Sulphur Springs, West Virginia, where public education for Black students simply stopped after eighth grade, she counted everything, started high school at 10, and graduated college summa cum laude at 18 with a professor inventing new ...