But astronauts weren't keen on "putting their lives in the care of the electronic calculating machines, which were prone to hiccups and blackouts," according to NASA. So Glenn asked engineers to "get the girl," referring to Johnson, to run the computer equations by hand. "If she says they're good,'" Johnson remembered Glenn saying, "then I'm ready to go."
https://www.nbcnews.com/news/us-news/katherine-johnson-nasa-mathematician-depicted-hidden-figures-dead-101-n1141566