The Woman Whose Software Guided the Apollo Missions Has Died Margaret Hamilton, the first female programmer hired to work on the space project at M.I.T., was 90.
Margaret Hamilton, who led the 100-person team that wrote the onboard software for the Apollo missions, guiding Neil Armstrong and Buzz Aldrin to a safe landing on the moon, died Sept. 30 in Cambridge, Mass. She was 90. Her death, in a hospital, was confirmed by her daughter, Lauren.
Ms. Hamilton was a young mathematician at the Massachusetts Institute of Technology in the early 1960s, putting her husband through law school by working in a computer lab. When she learned that M.I.T. was designing in-flight computers for the moon mission, she eagerly joined the team.
She was the first female programmer hired to work on the Apollo project, housed at M.I.T.’s Instrumentation Laboratory, in 1965. Her skills led to her promotion to director of software engineering on the project, which developed the two 70-pound onboard computers for the Apollo flights: one in the command module, which carried the astronauts from Earth, and the second in the lunar module, which set down on the moon’s surface.
Ms. Hamilton, who would bring her young daughter to work on weekends and evenings, is credited with popularizing the term “software engineering” to describe the complexity of the work her team did, thus elevating software coding to a status equal to hardware design.
The 72KB Computer That Went to the Moon
Primary navigation for the Apollo flights was guided from Houston on mainframe IBM computers. But the onboard Apollo Guidance Computer that the M.I.T. lab created was a crucial cog.
Developing its software was a major lift in an era when computers had limited memory. The onboard computers contained only 72 kilobytes of storage memory (an iPhone 16, by comparison, can have more than seven million times as much storage).
As Apollo 11’s lunar module, Eagle, touched down on the moon on July 20, 1969, Ms. Hamilton, then 32, was patched into Mission Control in Houston from M.I.T.
“I was not concentrating on the mission per se, I was concentrating on the software,” she recalled in a 2017 interview for the Computer History Museum. She compared the moment before touchdown to the instant before death when a person’s life is said to flash before them. “I could see the Apollo life, just: ‘Look what happened. We did it. It worked,’” she recalled. “It was exciting.”
The Alarm That Saved Apollo 11
But it almost didn’t happen. As Eagle neared the moon, its onboard computer famously flashed alarms, and Mission Control was faced with a decision about whether to abort the landing.
One of the astronauts, according to some historians, flipped a switch that overloaded the computer’s processing unit, which set off the alarms. Ms. Hamilton had foreseen just such an event. Her software told the onboard computer to prioritize essential tasks and cancel less important ones. The alarm was the signal that the procedure had occurred. Houston chose to continue the mission, and Eagle’s computer guided it to a safe landing on the Sea of Tranquillity.
“If the computer hadn’t recognized this problem and taken recovery action, I doubt if Apollo 11 would have been the successful moon landing it was,” Ms. Hamilton wrote in a 1971 letter to a computer magazine, Datamation.
Ms. Hamilton worked on the six lunar landing missions from 1969 to 1972. Her programming also contributed to Skylab, America’s first space station, launched in 1973, and to the early design of the space shuttle. She left M.I.T. to found a company, Higher Order Software, in 1976, as well as a second firm a decade later, Hamilton Technologies.
In 2016, President Barack Obama awarded Ms. Hamilton the Presidential Medal of Freedom. Its citation reads that her work for NASA “set the foundation for modern, ultrareliable software design and engineering.”
In 2019, on the 50th anniversary of the moon landing, Google trained more than 100,000 mirrors at its Ivanpah solar power farm in the Mojave Desert to create a nighttime portrait in reflected moonlight of Ms. Hamilton, bigger than Central Park.
Early Life and the "Rope Mother"
Margaret Elaine Heafield was born on Aug. 17, 1936, in Paoli, Ind. She enrolled in the University of Michigan before transferring to Earlham College where she received a bachelor’s degree in mathematics in 1958. Her first job at M.I.T., in 1959, was in the meteorology department for Edward Norton Lorenz, the founder of modern chaos theory.
She became known as the “rope mother,” because of the unusual way code was stored on the in-flight computers. Programs were written in binary, stored using copper wires woven around tiny doughnut-shaped cores. A wire passing through a core was read as a 1 and a wire that bypassed a core was a 0. The long assemblages were called ropes, woven by women capable of fine hand work.
Like most of the legions of engineers behind the moon landings, Ms. Hamilton was little known to the public, but in 2017 she achieved pop culture eminence with the introduction of Lego Margaret Hamilton, a play figure that was part of a Women of NASA set.
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