…worldwide communications network, linking tracking stations around the world to computers in Washington, Cape Canaveral, Florida, and Bermuda.
The computers had been programmed with orbital equations that would control the trajectory of the capsule in Glenn’s Friendship 7 mission, from blast off to splashdown, but the astronauts were wary of putting their lives in the care of the electronic calculating machines, which were prone to hiccups and blackouts.
As a part of the preflight checklist, Glenn asked engineers to “get the girl” — Johnson — to run the same numbers through the same equations that had been programmed into the computer, but by hand, on her desktop mechanical calculating machine.
“If she says they’re good,” Johnson remembers Glenn saying, “then I’m ready to go.” Glenn’s flight was a success, and marked a turning point in the competition between the U.S. and the Soviet Union in space.