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What it took to be a NASA computer

24 January 2017

Female computers, including those acclaimed in the hit film Hidden Figures, played a crucial role in developing the complex mathematical models that guided flight within and beyond Earth’s atmosphere in the mid 20th century.

NASA computers

Figure 1. Katherine Johnson sits at her desk with a calculating machine and a special globe known as a celestial training device. Credit: NASA

Hidden Figures, the period drama about African American women who worked as human computers at NASA, has now been nominated for three Academy Awards, including best picture. The movie, based on the real-life stories told in Margot Lee Shetterly’s book, has been a hit with audiences and critics (see the review in Physics Today).

Viewers particularly interested in physics and engineering may leave the film wondering how NASA came to employ so many women, as well as what tasks the computers performed. Although the women were initially hired to take “menial” work off the hands of male engineers, they quickly proved essential for achieving NASA’s soaring goals. Throughout World War II and the space race, the computers played a crucial role in everything from improving airplane stability to charting spacecraft trajectories.

Figure 2

Figure 2. These graphs show the pressure at different points on the wing of a test plane traveling at Mach 0.73 (901 km/h). Cp is a pressure coefficient; CNA is an airplane normal-force coefficient. Credit: NASA

Computers at NACA

The first human computers at the Langley Memorial Aeronautical Laboratory in Hampton, Virginia, were hired in 1935 by NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). As the aeronautical industry expanded and the defense industry sought to prepare for a possible war, NACA’s engineers “were getting pretty busy,” according to NASA historian Bill Barry. NACA sought to lighten their workload by bringing in people who could take experimental data from wind tunnels and test flights and perform the time-intensive calculations that the engineers needed to analyze the success of their designs.

Over the course of the 19th century, it had become more and more common for such calculating work to be assigned to women. Women with mathematical skill had fewer educational and professional opportunities than their male counterparts and therefore were usually cheaper to hire. Some at NACA initially balked at the idea of hiring women computers—but not because they were women. The concern was that the calculating machines that would have to be purchased for the computers were too expensive (see figure 1). That worry quickly vanished after the first five women began work at NACA. As one internal memo put it, “The engineers admit themselves that the girl computers do the work more rapidly and accurately than they could.”

In 1941 President Franklin D. Roosevelt signed Executive Order 8802, requiring federal agencies to hire workers without regard to “race, creed, color, or national origin.” The order came at a time when NACA was rapidly growing—it would triple in size by the end of World War II—and was struggling to find enough computers. NACA quickly began recruiting from a previously untapped talent pool: African American women.

One of the first black computers at Langley was Dorothy Vaughan, a math teacher who had been making ends meet as a laundress during summer breaks. Vaughan was offered a salary of $2000 per year (around $28 000 in today’s money), more than twice what she had been making as a teacher in segregated Virginia.

The daily work of a computer

At NACA, researchers were heavily engaged in analyzing aircraft design and performance. Figure 2, for example, shows four graphs from a 1958 NACA report on the aerodynamics of a research airplane called the D-558-II, the first aircraft to exceed Mach 2. The plots show changes in wing pressure distribution as the amount of lift changed.

Figure 3

Figure 3. This matrix, which appears in a 1967 NASA research report coauthored by Katherine Johnson, predicts the future location of a spacecraft based on current position. Credit: NASA 

Computers were involved at almost every stage of compiling and processing such data. Some would read the data recorded by pressure manometers, which printed pressure traces onto long strips of film. The women would use drafting tools and magnifying glasses to read and transcribe what the manometer had recorded during a test flight. Women in the computing pool would then process that data, performing hundreds of calculations of values such as lift, drag, and normal force coefficients and generating charts and graphs for the engineers to include in their reports. Those graphs and charts were copied by technical illustrators—usually men—before going to the printer.

The most skilled computers not only crunched numbers, but also collaborated with engineers and helped build the mathematical models that were used to correct engineering problems or plan spaceflights. Katherine Johnson (pictured in figure 1), one of the central characters in Hidden Figures, is an outstanding example of a computer who, as Barry put it, “pushed the engineers she was working with” and suggested alternate ways of tackling problems.

Johnson began working at NACA in 1953 and was temporarily assigned to the Flight Research Division. The division never returned her to the computing pool. After NACA became NASA, Johnson joined the Space Task Group, where she worked on techniques for predicting and directing the flight paths of satellites and, later, manned spacecraft.

In 1967, for example, Johnson coauthored the report Midcourse-Guidance Procedure with Single Position Fix Obtained from Onboard Optical Measurements with her colleagues Harold Hamer and W. Thomas Blackshear. The report detailed methods for manually determining the guidance of a manned spacecraft should automatic guidance fail somewhere between Earth and the Moon. The work required extensive knowledge of both analytical geometry, which was used to measure a spacecraft’s position based on its location relative to visible stars, and linear algebra for predicting the craft’s trajectory.

Figure 4

Figure 4. These 6×6 transition matrices in the 1967 report were used to predict nonlinear changes in flight positions at different distances from the Moon. Credit: NASA

Figure 3 shows the basic matrix mechanics used to predict a craft’s position at a future time T1 based on its position at time Tpf. The theoretical matrix would have been applicable only to relatively small, linear changes—not the types of changes astronauts or scientists should expect to observe in an actual flight, particularly as a craft approached an object with significant gravitational pull like the Moon. Later in the report, Johnson and her coauthors provided specific state-transition matrices that could be used for guidance calculations at different distances from the Moon (figure 4).

An essential part of the space race

Leaders at NACA and NASA regarded the computers as a crucial part of the agency’s research operations. Barry points to one particularly striking illustration of the computers’ importance: They were given the opportunity to take extended leave after giving birth and then return to NASA. That was a remarkable policy in an era when many women were expected to resign from their jobs after marriage; maternity leave was unheard of. Some research facilities even had day-care centers to enable talented computers to continue their work.

Despite the agency’s reliance on the female computing staff, Johnson was one of the few to get coauthor credit on engineers’ reports. Perhaps because of the thin paper trail, the NACA and NASA computers faded into the historical background—until, thankfully, their crucial role in 20th-century aeronautics and spaceflight was rediscovered by Shetterly and other writers.

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