In 1982 Sally Ride became the first American woman and the third woman in history to fly to space. But Ride and the other women in her 1978 astronaut class were not the first female astronaut trainees: That distinction went to the “Mercury 13,” though they’re only now getting the recognition they deserve. Those 13 women underwent extreme physical tests developed as part of NASA’s astronaut selection process in 1961 but never made it to space. NASA, according to an upcoming Netflix documentary, wasn’t interested in female candidates. Even if they had the “right stuff,” they were the wrong gender.

Directed by David Sington and Heather Walsh, Mercury 13 tells the story of the 13 women and the uphill battle they faced in becoming part of Project Mercury, the first U.S. spaceflight program. They were part of a short-lived, privately funded project called Lovelace’s Women in Space Program, an Air Force project meant to determine whether women, on average smaller and lighter than men, were better equipped to go to space. This program wasn’t publicized in its time, much like the incredible women that served as “human computers” profiled in the hit 2016 film Hidden Figures.

Mercury 13 documentary
The poster for "Mercury 13."

At its start, Brigadier General Donald Flickinger and Dr. William Lovelace II, who also served as the head of NASA’s Special Committee on Bioastronautics, invited top-notch pilot Jerrie Cobb to undergo the same intense physical training Lovelace was developing for NASA’s male candidates. Cobb passed the tests, and they went on to recruit other first-class female pilots. Ultimately, 13 women passed the examinations, eight of whom are alive today and are profiled in the documentary.

Ultimately NASA shut down the secret program and focused on the now-famous Mercury 7, the male astronauts that became the first Americans in space. Cobb, a certifiable badass, few to Washington, D.C. and lobbied for her team before the Subcommittee of the House Committee on Science and Astronautics — hearings that investigated sex discrimination two years before the 1964 Civil Rights Act outlawed that bias.

John Glenn, who was portrayed as a very woke man in Hidden Figures, was actually not that cool about women becoming astronauts. He and astronaut Scott Carpenter testified that women couldn’t qualify as astronaut candidates, saying that they needed to be graduates of military jet test pilot programs, which wasn’t available to women in the early 1960s.

In interviews at the time, Cobb was asked whether there was a need for women in space. She turned it around: “If we’re going to send a human being into space, then we should send the one most qualified.” With Mercury 13, which premieres April 20, Cobb and her peers get the definitive word, even if it’s long overdue.