Margaret Hamilton, who led Apollo flight software at MIT, dies at 90

Margaret Hamilton, the computer scientist who led the software team at MIT's Instrumentation Lab during NASA's Apollo program, died on Sep. 30. She was 90.

Hamilton wrote more than 130 publications and helped make software engineering a discipline in its own right. She worked at MIT from 1959 until the mid-1970s, then became a computing entrepreneur and CEO. In 2016, President Barack Obama gave her the Presidential Medal of Freedom. The citation said she "defined new forms of software engineering and helped launch an industry that would forever change human history."

Olivier de Weck, the Apollo Program Professor and interim head of MIT's Department of Aeronautics and Astronautics, said it would be "a dramatic understatement" to call her ahead of her time. He said she led a team using a very young technology to build one of the most complex systems humans had made.

Hamilton was born in Paoli, Indiana, in 1936. She studied mathematics at the University of Michigan, then transferred to Earlham College, where she earned a BA in mathematics with a minor in philosophy in 1958. In 1959 she moved to Boston with her husband, who was studying law.

Her first job there was a temporary post in MIT's meteorology department. She worked with professor Edward N. Lorenz on weather prediction software. It was her first real work in programming, and it went on to inform Lorenz's later publications on chaos theory.

In 1961 she became a programmer at MIT Lincoln Laboratory. She worked on SAGE, the first air defense system in the United States. Her code ran on a prototype computer that the U.S. Air Force used to search for potentially unfriendly aircraft. This is where she became interested in software reliability, which was a new idea at the time.

In 1965, she was getting ready for graduate studies when her husband saw a newspaper ad. MIT's Instrumentation Lab wanted people to build software to "send man to the moon." The lab had won the NASA contract for Apollo's onboard flight software. Hamilton applied and became the first programmer hired for Apollo at MIT, and the first woman programmer on the project.

She started on software for the uncrewed missions. She was then promoted to lead the team writing onboard software for crewed flights. By 1968 she was assistant director in charge of the Command and Service Module team, and more than 400 people worked on Apollo software.

Looking back in 2009, she told MIT News that the work was as exciting as the missions themselves. "There was no second chance. We knew that," she said. She added that management gave the team total freedom and trust because software was such a mystery to them.

One episode became known as "the Lauren error." Hamilton's daughter Lauren, then four, was playing with the command module simulator at the lab. She somehow started a pre-launch program, called P01, while the simulator was in midflight, and the simulator crashed.

Hamilton added a warning to the technical documentation not to run P01 during flight. She also proposed a software fix for real missions. She was overruled, because highly trained astronauts would never make that mistake.

Then, during Apollo 8 in 1968, Jim Lovell accidentally launched P01 in flight, and navigation data vanished. Hamilton and her team were called in to fix it. Her proposed changes were added afterward. It was an early example of "defensive" programming, which means building software that can anticipate or fix errors on its own.

Her best-known contribution came during Apollo 11 in July 1969. Just before the Eagle module landed on the moon, the onboard computer raised a 1202 alarm. The computer was overloaded because of a fault in a hardware switch, and it might not have been able to handle the landing.

But Hamilton's team had built priority-driven software. It could drop unnecessary background tasks and focus on the ones the mission depended on. Houston trusted the software and let the mission go ahead. Two men then walked on the moon for the first time.

Hamilton kept working at the Instrumentation Lab into the 1970s. As Apollo wound down, the lab split from MIT and became the independent Draper Laboratory. Draper's president and CEO, Jerry M. Wohletz, said she "left an indelible mark" on the lab and helped ensure Apollo astronauts landed safely and returned home.

In 1976 she started her first software company, Higher Order Software. It was built around her approach of preventing errors and tolerating faults. A decade later she founded Hamilton Technologies. Its main product is the Universal Systems Language, a way of modeling and engineering complex software with a focus on error prevention.

She spent much of her career pushing for software engineering to be taken seriously. She told El Pais in 2018 that the term was once considered "quite amusing" and a running joke. "Software eventually and necessarily gained the same respect as any other discipline," she said.

Her honors include NASA's Exceptional Space Act Award in 2003, the Computer History Museum Fellow Award in 2017, the Intrepid Lifetime Achievement Award in 2019, and induction into the National Aviation Hall of Fame in 2022.

Later in life she became an icon for women in science and technology. A well-known photo of her next to a printout of her team's Apollo code spread online. In 2015, the Apollo software she helped develop was posted in full on GitHub. In 2017 she became an official Lego Minifigure, from a set designed by MIT science communicator Maia Weinstock honoring women of NASA history.

De Weck said her career was dedicated to preventing errors and what she called "handling the unknown."

Hamilton is survived by her daughter, Lauren Hamilton; her son-in-law, Richard Selesnick; two grandsons; four great-grandchildren; and her siblings John, David, and Kathryn. A memorial service will be held in the spring in Cambridge, Massachusetts.