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 moon landing, died September 30 in Cambridge, Massachusetts. She was 90 years old.
His death in hospital was confirmed by his daughter, Lauren.
Ms. Hamilton was a young mathematician at the Massachusetts Institute of Technology in the early 1960s, where her husband was studying law while working in a computer lab. When she learned that MIT was designing onboard computers for the lunar mission, she enthusiastically joined the team.
She was the first female programmer hired to work on Project Apollo, housed at MIT’s Instrumentation Laboratory, in 1965. Her skills led to her being promoted 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 transported the astronauts from Earth, and the second in the lunar module, which landed on the surface of the Moon.
Ms. Hamilton, who brought 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, elevating software coding to the same status as hardware design.
A 1969 photograph of Ms. Hamilton, 5 feet 10 inches tall, standing next to a tall stack of printed codes developed for the moon landing, has been widely shared on social media in recent years.
Primary navigation for the Apollo flights was guided from Houston on central IBM computers. But the onboard Apollo guidance computer created by the MIT lab was a crucial cog.
The development of his software was a major advance at a time when computers had limited memory. The onboard computers only contained 72 kilobytes of storage memory (an iPhone 16, by comparison, can have more than seven million times more storage).
As Apollo 11’s lunar module, Eagle, landed on the Moon on July 20, 1969, Ms. Hamilton, then 32, was connected to MIT Mission Control in Houston.
“I wasn’t focused on the mission itself, I was focused on the software,” she recalled in a 2017 interview for the Computer History Museum. She compared the moment before landing to the moment before death, when a person’s life flashes before them. “I could see Apollo’s life, just, ‘Look what happened. We did it. It worked,'” she recalls. “It was exciting.”
But that almost didn’t happen. As Eagle approached the moon, its onboard computer sounded alarms and Mission Control was faced with the decision of whether or not to abort the landing.
According to some historians, one of the astronauts flipped a switch that overloaded the computer’s processing unit, triggering the alarms. Mrs. Hamilton had planned such an event. Its software instructed the onboard computer to prioritize essential tasks and cancel less important ones. The alarm was the signal that the procedure had taken place. Houston chose to continue the mission and Eagle’s computer guided him to a safe landing on the Sea of Tranquility.
“If the computer had not recognized this problem and taken recovery measures, I doubt that Apollo 11 would have made the successful moon landing,” Ms. Hamilton wrote in a 1971 letter to the computer magazine Datamation.
Ms. Hamilton worked on all six moon landing missions from 1969 to 1972. Her programming also contributed to Skylab, the first American space station, launched in 1973, as well as the first design of the Space Shuttle. She left MIT to found a company, Higher Order Software, in 1976, as well as a second company a decade later, Hamilton Technologies.
In 2016, President Barack Obama awarded Ms. Hamilton the Presidential Medal of Freedom. His citation states that his work for NASA “laid the foundation for modern, ultra-reliable software design and engineering.”
In 2019, on the 50th anniversary of the moon landing, Google angled more than 100,000 mirrors at its Ivanpah solar farm in the Mojave Desert to create a nighttime portrait of Ms. Hamilton in reflected moonlight, larger than Central Park.
Margaret Elaine Heafield was born August 17, 1936, in Paoli, Indiana, the eldest of four children of Kenneth and Esther (Partington) Heafield. The family moved to the Upper Peninsula of Michigan. His mother was a high school teacher and his father was a poet and professor of English and philosophy.
Margaret enrolled at the University of Michigan before transferring to Earlham College in Richmond, Indiana, where she earned a bachelor’s degree in mathematics in 1958.
The same year she married James Hamilton, also a student at Earlham. The couple moved to Cambridge, Massachusetts, where their plan was for Mrs. Hamilton to support her husband through law school and then make him pay the bills while she earned a doctorate in mathematics and became a professor.
Instead, her computer work took her in a completely different direction.
Her first job at MIT, in 1959, was in the meteorology department of Edward Norton Lorenz, the founder of modern chaos theory, for whom she helped develop weather forecasting software.
In 1961, she joined an MIT team working for the Air Force on a system known as SAGE for tracking enemy aircraft. He was given a riddle reserved for all new programmers: deciphering a program that no one could put to work, and whose author had left notes in Latin and Greek. Ms. Hamilton was the first person to launch the program.
Based on her work on SAGE, she was hired for the MIT Apollo computer project, led by an aeronautical engineering professor, Charles Stark Draper, who had won the NASA contract for the navigation and guidance system for the lunar flight, announced by President John F. Kennedy in 1961.
Ms. Hamilton was initially the only woman on the programming team, she recalled at a 2021 conference on the history of the Apollo computers.
It became known as the “mother of rope”, due to the unusual way in which code was stored on on-board computers, in an era before the widespread use of silicon chips.
The programs were written in binary arithmetic, a series of 1s and 0s. The numbers were stored using copper wires woven around tiny donut-shaped materials called cores. A wire passing through a core was read as a 1 and a wire going around a core was a 0. Long assemblies of cores and threaded wire were called ropes.
The ropes were woven by women capable of careful handwork, many of whom had worked in New England textile mills. Mrs. Hamilton, responsible for ensuring that everything went smoothly, was the “mother of the rope.” (A 1965 film shows how computers designed by MIT were built in Raytheon’s space division factory in Waltham, Massachusetts).
Her first marriage ended in divorce in 1967. Two years later, she married Daniel Lickly (pronounced “probable”), a supervisor on MIT’s Project Apollo, who was responsible for hiring her. They divorced in the early 1970s.
From the late 1970s, Ms. Hamilton was the partner of Ron Hackler, a musician whom she met when he helped her move her office, then trained in systems engineering and was employed at his company Hamilton Technologies, which developed software. He died in 2025.
In addition to her daughter Lauren, Mrs. Hamilton is survived by two grandsons, four great-grandchildren and her siblings John, David and Kathryn Heafield (pronounced “hayfield”).
Like most of the legions of engineers, mathematicians and scientists who worked behind the scenes to make the moon landings happen, Ms. Hamilton is little known to the public.
But in 2017, she achieved something of a pop culture eminence with the introduction of Lego Margaret Hamilton, a play figure that was part of a Women of NASA set. She is shown with long hair and wearing glasses, standing next to a wobbling pile of computer codes.
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