In the early 1960s, 13 trailblazing American women participated in a secret program to become America’s first female astronaut. Although the skilled pilots passed the same physiological screening tests given to the Mercury Seven astronauts, NASA abruptly shuttered the little-known Woman in Space Program before its participants could ever leave the ground. The “Mercury 13” may have had the right stuff, but for NASA they were the wrong gender.

When NASA introduced its first astronaut corps in 1959, it was strictly a men’s-only club. Although women weren’t explicitly barred from the “Mercury Seven,” NASA’s requirement that astronauts be experienced military jet test pilots—a job open only to men—effectively prevented their selection.

However, space medicine experts such as Air Force Brigadier General Donald Flickinger and Dr. Randy Lovelace, a NASA contractor who conducted the official physical examinations of the Project Mercury candidates, believed that women could be preferable to men as astronauts because on average they are lighter, shorter and consume less food and oxygen—an advantage when every pound is critical to the cost and feasibility of space flight. In addition, tests have found women more resistant to radiation and less prone to cardiovascular issues.

After a chance encounter, Flickinger and Lovelace found their perfect candidate for testing an aspiring female astronaut. Like many young pilots at the dawn of the Space Age, Jerrie Cobb had stars in her eyes. A licensed commercial pilot at the age of 18, Cobb was flying routes from California to Paraguay by the time the Associated Press profiled the 24-year-old “girl pilot” in 1955. Five years later, Cobb had logged a total of 10,000 hours in the cockpit, twice that of Mercury astronaut John Glenn.

In February 1960, the 29-year-old Cobb traveled to Lovelace’s private clinic in Albuquerque, New Mexico, as the first participant in his secret Woman in Space Program, which was not sanctioned by NASA. She underwent the same grueling tests given to the Mercury Seven. Researchers poured ice water into her ears to simulate vertigo and jammed a 3-foot rubber hose down her throat to test stomach acid. She was poked and prodded with needles and submerged in water and darkness to simulate sensory isolation.

Cobb not only passed all three phases of the screening program, she even surpassed the male astronauts on some tests. When Lovelace announced the test results in August 1960, Cobb became a media sensation. She appeared in Life magazine, and newspapers debated whether to call the would-be space traveler an “astronautrix,” “astronette” or “lady astronaut.”

To see if Cobb’s results could be replicated, Lovelace recruited another two-dozen skilled female pilots—ranging from 21-year-old flight instructor Wally Funk to 39-year-old Janey Hart, a mother of eight and wife of Senator Philip Hart—to come to New Mexico. Famed aviatrix Jackie Cochran, the first woman to break the sound barrier, used some of the money from her successful cosmetics business to bankroll the privately run program. As with Cobb, the women outperformed the men on numerous medical and screening tests. Funk, who grew up playing with planes instead of dolls, spent more than 10 hours in the isolation tank—better than any other astronaut trainee, male or female.

A dozen women, whom Cobb called Fellow Lady Astronaut Trainees (FLATs), passed the screening. Later dubbed the “Mercury 13,” the aspiring astronauts prepared to undergo space flight simulation at a Navy facility in Pensacola, Florida. Just days before leaving, however, Lovelace sent word that the testing had been abruptly cancelled once the Navy learned that his program was not sponsored by NASA.

After NASA shuttered the Woman in Space Program, Cobb and Hart met in person with Vice President Lyndon Johnson in March 1962 to lobby for its resumption. According to Stephanie Nolen’s book “Promised the Moon: The Untold Story of the First Women in the Space Race,” Johnson aide Liz Carpenter drafted a letter to NASA asking why women couldn’t be astronauts. After meeting with Cobb and Hart, Johnson picked up his pen, but instead of signing the letter, he scrawled, “Let’s stop this now!”

Cobb and Hart fared no better on Capitol Hill when they testified before a congressional subcommittee in July 1962. “We seek, only, a place in our nation’s space future without discrimination,” said Cobb, who was referred to in United Press International reports as “an attractive 31-year-old astronaut aspirant.” “There were women on the Mayflower and on the first wagon trains west, working alongside the men to forge new trails to new vistas. We ask that opportunity in the pioneering of space.”

“I think that our society should cease to frown on the woman who seeks to combine family life with a career,” Hart told lawmakers. “Let’s face it: For many women the PTA just is not enough.”

Still being showered with adulation five months after becoming the first American to orbit the Earth, Glenn backed NASA’s position that a new training program for women would jeopardize the goal of landing an American on the moon before the end of the decade. Glenn told lawmakers that although he believed women had the capabilities to become astronauts, “I think this gets back to the way our social order is organized, really. It is just a fact. The men go off and fight the wars and fly the airplanes and come back and help design and build and test them.”

The Mercury 13 found no more support in Congress than they had in the White House for women becoming astronauts or military test pilots. NASA hired Cobb as a consultant on women’s issues, but then gave her little to do. “I’m the most unconsulted consultant in any government agency,” she groused after a year on the job. Her frustration only grew when Soviet cosmonaut Valentina Tereshkova became the first woman in space in 1963. By the time Cobb resigned her position with NASA, the closest she had ever come to outer space was posing with a Mercury spaceship capsule for newspaper photographers.

When Neil Armstrong took one small step for a man—not a woman—after landing on the moon in July 1969, Cobb was deep in the jungles of the Amazon using her piloting skills to deliver food, medicine and humanitarian aid packages to villages, work for which she would later be nominated for a Nobel Peace Prize. Not until 1983 did an American woman, Sally Ride, blast off into space. In 1995, eight of the 11 surviving FLATs, including Cobb, gathered together to watch as Eileen Collins roared into space as the first female space shuttle commander, a dream denied to the trailblazers but made possible for Collins by their efforts.