How Margaret Hamilton Wrote the Computer Code That Helped Save the Apollo Moon Landing Mission

From a distance of half a century, we look back on the moon landing as a thoroughly analog affair, an old-school engineering project of the kind seldom even proposed anymore in this digital age. But the Apollo 11 mission could never have happened without computers and the people who program them, a fact that has become better-known in recent years thanks to public interest in the work of Margaret Hamilton, director of the Software Engineering Division of MIT's Instrumentation Laboratory when it developed on-board flight software for NASA's Apollo space program. You can learn more about Hamilton, whom we've previously featured here on Open Culture, from the short MAKERS profile video above.

Today we consider software engineering a perfectly viable field, but back in the mid-1960s, when Hamilton first joined the Apollo project, it didn't even have a name. "I came up with the term 'software engineering,' and it was considered a joke," says Hamilton, who remembers her colleagues making remarks like, "What, software is engineering?"




But her own experience went some way toward proving that working in code had become as important as working in steel. Only by watching her young daughter play at the same controls the astronauts would later use did she realize that just one human error could potentially bring the mission into ruin — and that she could minimize the possibility by taking it into account when designing its software. Hamilton's proposal met with resistance, NASA's official line at the time being that "astronauts are trained never to make a mistake."

But Hamilton persisted, prevailed, and was vindicated during the moon landing itself, when an astronaut did make a mistake, one that caused an overloading of the flight computer. The whole landing might have been aborted if not for Hamilton's foresight in implementing an "asynchronous executive" function capable, in the event of an overload, of setting less important tasks aside and prioritizing more important ones. "The software worked just the way it should have," Hamilton says in the Christie's video on the incident above, describing what she felt afterward as "a combination of excitement and relief." Engineers of software, hardware, and everything else know that feeling when they see a complicated project work — but surely few know it as well as Hamilton and her Apollo collaborators do.

Related Content:

Margaret Hamilton, Lead Software Engineer of the Apollo Project, Stands Next to Her Code That Took Us to the Moon (1969)

How 1940s Film Star Hedy Lamarr Helped Invent the Technology Behind Wi-Fi & Bluetooth During WWII

Meet Grace Hopper, the Pioneering Computer Scientist Who Helped Invent COBOL and Build the Historic Mark I Computer (1906-1992)

How Ada Lovelace, Daughter of Lord Byron, Wrote the First Computer Program in 1842–a Century Before the First Computer

Based in Seoul, Colin Marshall writes and broadcasts on cities, language, and culture. His projects include the book The Stateless City: a Walk through 21st-Century Los Angeles and the video series The City in Cinema. Follow him on Twitter at @colinmarshall, on Facebook, or on Instagram.


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