On November 24, 2015, President Barack Obama awarded the Presidential Medal of Freedom, considered the nation’s highest civilian honor, to 17 men and women. Among them was 97-year-old retired African-American NASA mathematician Katherine G. Johnson, selected for her contributions to the space program, starting with the Mercury missions in the ‘50s and early ‘60s, through the Apollo moon missions in the late ’60s and early ‘70s, and ending with the space shuttle missions in the mid '80s. Among other things, she calculated the trajectories of America's first manned mission into orbit and the first Moon landing.

Awarding Johnson this well-deserved honor doesn't just shine a spotlight on a single black female STEM pioneer. It also illuminates an obscure but important piece of history. Johnson was just one of dozens of mathematically talented black women recruited to work as “human computers” at the Langley Memorial Research Laboratory in the ‘40s and ‘50s. (Many of whom, including Johnson, are the subject of Theodore Melfi's Oscar-nominated film, Hidden Figures.)

They were so named because before machines came along, they crunched the numbers necessary for figuring out everything from wind tunnel resistance to rocket trajectories to safe reentry angles.

In fact, all of Langley’s hundreds of “human computers,” whether black or white, were women. It was an era when, as Johnson put it, “the computer wore a skirt.”

Considering society’s longheld prejudices about women and math, it may surprise some that NASA (then NACA, or the National Advisory Committee on Aeronautics) would allow these "skirts" to work there in the first place. But the same man shortage that handed Rosie her rivets when the U.S. entered WWII in 1941 handed the human computers their slide rules.

That year, FDR signed an order to hire more African-American workers, and two years later, in 1943, Langley started hiring college-educated black women with a background in math and chemistry.

Though the job (at $2000 a year) was far better paid than most available for educated women at the time, such as nursing or teaching, the black mathematicians, or computers, faced segregation in Hampton, Virginia, where NACA set up its research lab. They worked in a separate facility from the white computers, had to use separate washrooms, and had to sit at a colored table in the cafeteria. A few years into the program, the unmarried white computers were housed in a fancy dorm. Meanwhile, the unmarried black computers had to find lodging in town, which wasn’t always easy. The lab was even on the site of a former plantation.

Despite the systematic discrimination, these mathematicians kept calculating.

“They’re more resilient than I could imagine,” said Duchess Harris, an American Studies professor at Macalester College in Minnesota who is part of the “Human Computer Project,” which launched last year. It's a collaboration between Harris, recent Macalester grad Lucy Short, and Margot Lee Shetterly, researcher and author of Hidden Figures: The Untold Story of the African American Women Who Helped the United States Win the Space Race.

As part of the project, the three women toured the lab and saw where the black mathematicians worked, in a building a mile away from the white ones. The building had no restroom facilities, Harris said.

Such details are personal to Harris, because her grandmother, Miriam Daniel Mann, was one of the first black computers at Langley. A former math teacher, Mann worked for the lab until 1966, when illness forced her to retire. She died in 1967, two years before the lunar landing. Among other things, she worked on the Mercury program along with Johnson, crunching numbers for Alan Shepard and John Glenn’s flights.

Unlike Mann, Johnson did not have to work in a separate building for long. Hired in 1953, she was first put in the computer pool, but in just weeks was working more closely with engineers, a promotion she credited to her asking them incessant questions about the material. One such question was: Why weren’t women allowed to attend meetings and briefings? Was there a law?

There wasn’t. In five years, Johnson became the only non-white, non-male member of the Space Task Force, charged with getting American astronauts into space as soon as possible. When that happened for the first time three years later, in 1961, Johnson's calculations for Alan Shepard’s capsule trajectory played a crucial role.

"The early trajectory was a parabola, and it was easy to predict where it would be at any point," Johnson told Langley’s in-house newsletter, Researcher News, in 2008. "Early on, when they said they wanted the capsule to come down at a certain place, they were trying to compute when it should start. I said, 'Let me do it. You tell me when you want it and where you want it to land, and I'll do it backwards and tell you when to take off.' That was my forte."

When it was John Glenn’s turn to go up, NASA had started using machines for such calculations. But Glenn, who mistrusted this new technology, insisted that Johnson double-check the results.

"You could do much more, much faster on a [machine] computer," Johnson told Researcher News. "But when they went to [machine] computers, they called over and said, 'Tell her to check and see if the computer trajectory they had calculated was correct.' So I checked it and it was correct." Glenn subsequently became the first American to orbit the Earth.

Johnson would go on to make her mark on future missions, including calculating the trajectory for Apollo 11 and then lending her expertise to the space shuttle program. And while today's ceremony honors only her, the other women should not be forgotten, including Mann, Mary Jackson, Dorothy Vaughan, and Kathryn Peddrew, to name only a few. All broke professional barriers for black women—and played key roles in getting us all closer to the stars.

This story originally ran in 2015.