The women computers of JPL, in 1953NASA / JPL-Caltech

In 1939, the National Academy of Sciences awarded a grant to the Suicide Squad, a group of three students experimenting with rockets at Caltech, now more formally known as the GALCIT (Guggenheim Aeronautical Laboratory at the California Institute of Technology) Rocket Research Project.

It came just in time.

Until then, the group, comprised of Frank Malina, Jack Parsons, and Ed Forman, had no way to fund the rockets they were working on, and was on the verge of disbanding. That first award, $1,000, rescued the group, bringing them back together. When they were awarded a second grant the next year for ten times as much, it was life-changing. It was the U.S. government’s first investment in rocket research. In deference to the Army Air Corps, which had proposed the funding, they changed their name to the Air Corps Jet Propulsion Research Project. Their goal was clear: Develop a rocket plane. The risky project was the beginning of what would become the Jet Propulsion Laboratory.

Knowing they would need skilled mathematicians, Frank approached his two friends, Barbara (Barby) and Richard Canright. Barby knew the job would be far from a sure thing. She wondered if she could depend on the longevity of the reckless group. She and Richard would be leaving good jobs to work for men who were not known for their reliability. Yet the offer was tempting.

If she accepted, Barby would once again be the only woman in a group of men. It was a job she hadn’t expected, yet one she was eminently qualified for. Math was a comfortable second skin. She would always feel more at home with a pencil in her hand than at a typewriter. In addition, the position held prestige, allowed her to work alongside her husband, and paid twice what she made as a typist. More than the money, it offered her the opportunity to use her neglected math skills.

It wasn’t just the rocket research group that Barby was becoming a member of. She was joining an exclusive group whose contributions spanned centuries. Before Apple, before IBM, and before our modern definition of a central processing unit partnered with memory, the word computer referred simply to a person who computes. Using only paper, a pencil, and their minds, these computers tackled complex mathematical equations.

Early astronomers needed computers in the 1700s to predict the return of Halley’s Comet. During World War I, groups of men and women worked as “ballistic computers,” calculating the range of rifles, machine guns, and mortars on the battlefield. During the Depression era, 450 people worked for the U.S. government as computers, 76 of them women. These computers, meagerly paid as part of the Works Progress Administration, created something special. They filled twenty-eight volumes with rows and rows of numbers, eventually published by the Columbia University Press as the plainly named Mathematical Tables Project series. What they couldn’t know was that these books, filled to the brim with logarithms, exponential functions, and trigonometry, would one day be critical to our first steps into space.

The dream of space exploration was what initially tugged at the Suicide Squad. They worked on engines during the day, but at night they talked about the limits of the universe.

At the time, rockets were considered fringe science, and the people who worked on them weren’t taken seriously. When Frank asked one of his professors at Caltech, Fritz Zwicky, for his help on a problem, the teacher told him, “You’re a bloody fool. You’re trying to do something impossible. Rockets can’t work in space.” In fact, the word rocket was in such bad repute that the group purposely omitted it when they formed their institute, the Jet Propulsion Laboratory. Some scientists at the sister Guggenheim Aeronautical Laboratory at the Massachusetts Institute of Technology snickered at them, while Vannevar Bush, an engineering professor at MIT, derisively said, “I don’t understand how a serious scientist or engineer can play around with rockets.”

* * *

The Canrights were enjoying a quiet Sunday afternoon on December 7, 1941. Barby was in the kitchen, cooking and listening to the radio, when the announcer interrupted the program with breaking news. The Japanese had attacked Pearl Harbor. Barby fell to the kitchen floor, tears streaming down her cheeks. The war had hit home. Hawaii suddenly seemed very close to California. Barby and Richard were glued to the radio for the rest of the evening. Barby knew that their work would now take on a new importance. Going in to the lab the next day, they might have been talking about Pearl Harbor, but they were thinking about the rocket plane. The army needed to lift a fourteen-thousand-pound bomber into the air.

In one month, Barby filled more than twenty notebooks with rows of neatly printed numbers. Each column represented a value from the experiment, plugged into lines of exquisitely complex equations. One of the key computations Barby was responsible for was the thrust-to-weight ratio, an equation that allowed the group to compare the performance of the engines under different conditions. She repeated the calculation many times, sliding the numbers into the equation with the ease of slipping on a pair of shoes.

It was all building to one singular achievement.

It took just a year for the JPL rockets to boost the Douglas A-20A bomber into the air. They experimentally fired the JATO units on the heavy bomber forty-four times, the rockets needing only minor fixes. The project was a success.

All JPL needed now was more employees. Barby was excited when Frank told her he was hiring two more computers, a man and a woman, Freeman Kincaid and Melba Nead. Until then, Barby and Frank’s secretary had been the only two women at the institute. Barby, who didn’t spend much time with the secretary, had felt the lack of female companionship.

Barby’s husband was promoted to engineer. It was what Richard had always hoped for. Although Barby’s experience was similar to his, she was not promoted and hadn’t expected to be. It was simply one of the limits of being female. Although she loved her work, with Richard’s promotion and subsequent added income, she was thinking about starting a family.

Not long after Richard’s promotion, JPL hired two more women, Virginia Prettyman and Macie Roberts, rounding out the computer room to a team of five: four women and one man. The new recruits didn’t seem promising at first. Virginia and Macie, or Ginny and Bobby, as they soon became known, had never heard of a computer before. They answered the want ad with little idea of what they were getting themselves into. Despite the newcomers’ naïveté, the computers immediately became good friends. They spent every day working together, sweating over their calculations, observing experiments in the test pits, and chatting with the engineers.

Macie Roberts's computing group circa 1955. Roberts is standing on the far right of the image, conferring with one of the other women. Barbara Paulson is on the telephone (standing, back left). Helen Ling is at the second desk in the left row. (NASA / JPL-Caltech)

The computer room worked as seamlessly as a machine, notebooks passed from desk to desk as the five colleagues spent their days transforming raw numbers into meaningful data. Their prize possession was a single Friden calculator. It looked nothing like the modern, sleek devices we’re used to today that can perform hundreds of functions and sit in the palm of our hand. Instead, the calculator was the size of a bread box and heavy. When they first received the Friden, Barby was excited to be in command of a machine that so few people knew how to use. It was the latest technology and much faster than a slide rule, though it could only add, subtract, multiply, and divide. It was a dull gray and looked like a typewriter, but instead of letters, the keyboard held rows of repeating numbers, from 0 to 9.

Melba, Macie, Virginia, Freeman, and Barby were responsible for calculating the potential of rocket propellants. During a conversation one day, Barby noted, “I hear Jack has an idea for a new one. …You’re not going to believe what it’s made of—asphalt.”

As crazy as it sounded to use the heavy asphalt that paved roads, no one knew what would best make rockets fly, so everything was fair game. At JPL, the team tested a wide range of solid, liquid, and gas options. They loaded the fuel and oxidizers into rocket motors that were housed in the test pits in a dirt field. These were directly adjacent to a handful of permanent buildings and the row of tarpaper shacks that made up the lab. Then they fired them.

The calculation the engineers and computers were most interested in was the specific impulse, the change in force that accumulates as a rocket uses fuel. Specific impulse indicates roughly how much momentum builds up as the propellant is being thrown out the back of the rocket. The faster the propellant is thrown, the faster the rocket can travel. Having a high specific impulse means less fuel is needed to go farther. This calculation is the simplest way to compare the effectiveness of different propellants. It took four different equations for the computers to get to the specific-impulse equation. They had to compute thrust and velocity first. They would then plug these numbers into a formula that calculated the thrust per unit mass flow of each propellant.

These calculations could not be done quickly, since they were all done by hand. It took only seconds for a rocket engine to be fired, but analyzing that one experiment could take a week or more for the human computers. Notebooks quickly accumulated, often six to eight of them for each experiment. Barby liked to stack them on her desk, forming a wall of paper. As the notebooks piled up, so did her feeling of accomplishment. Then, at the end of the experiment, after the final report was written up, she’d clear the notebooks off her desk.

The new propellant that Barby and Macie were excited about was a unique mixture of liquefied asphalt with a potassium perchlorate oxidizer. The computers still had to figure out what proportions of fuel and oxidizer were needed to work in a rocket. The best mixture, they calculated, was 70 percent Texaco No. 18 asphalt combined with 30 percent Union Oil lubricating oil. The technicians liquefied the asphalt-oil combination by heating it to 275 degrees Fahrenheit and then added crushed potassium perchlorate. The propellant was mixed and allowed to cool, becoming a solid round block, a cake of rocket-blasting power. They called it Jack’s cake..

The computers found that Jack’s unusual propellant had a specific impulse of 186 and an exhaust velocity of 5,900 feet per second. It delivered a formidable 200 pounds of thrust. It was exactly the kind of fuel the military needed, because it was powerful yet used common (and cheap) ingredients that could be stored at a wide range of temperatures. Almost immediately Barby saw her work finding its way into rockets owned by the U.S. Navy.

Over time, as Macie was rose in the ranks of JPL, Barby saw her future at the institute faltering. She was pregnant. It was getting harder and harder to conceal her growing belly at work, and she knew that soon she’d have to quit. There was no such thing as maternity leave. She was thrilled to be having a baby but sad to say good-bye to the group she’d been a part of since its birth.

Macie would go on to lead a team of young women who were about to leave the lives expected of them. Each would go from being an oddity in school, one of only a few girls who flourished in calculus and chemistry classes, to joining a unique group of women at JPL. The careers they were about to launch would be unlike any other.

This article has been adapted from Nathalia Holt’s book, Rise of the Rocket Girls: The Women Who Propelled Us, from Missiles to the Moon to Mars.

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