Margaret Hamilton, the computer scientist who led the team that wrote the onboard flight software for NASA's Apollo missions, has died at the age of 90. MIT, her former employer, confirmed her death and said she died on September 30. The cause of death was not disclosed.
Hamilton led the Software Engineering Division of the MIT Instrumentation Laboratory, which won NASA's first major Apollo contract in 1961. She ultimately led a team of about 100 engineers designing the software that guided the command and lunar modules — including the software that carried Neil Armstrong and Buzz Aldrin to the surface of the Moon in July 1969.
Her work mattered most in the final minutes of that landing. As the lunar module Eagle descended, the Apollo Guidance Computer triggered a series of alarms indicating "executive overflows" — the computer could not complete all of its tasks in real time and had to postpone some of them.
Hamilton's priority-driven software detected the overloads, dropped lower-priority tasks and re-established the highest-priority ones: the landing itself. Mission Control, with high confidence in the software, told the astronauts to proceed, and Eagle landed with only enough fuel for roughly 30 more seconds of flight.
"The software was not only informing everyone that there was a hardware-related problem, but that the software was compensating for it," Hamilton later said.
The underlying cause of the alarms remains disputed. A common account says the astronauts inadvertently left the rendezvous radar switch on, overloading the computer; that claim is disputed by Robert Wills of the National Museum of Computing, who linked the errors to data requests entered during the descent.
Hamilton had spent years preparing for exactly this kind of failure. After her four-year-old daughter Lauren crashed an Apollo command module simulator by pushing a button while "playing astronaut," Hamilton pushed for software backstops so an astronaut could not trigger the same failure in flight. The failsafe became known as "the Lauren error." A similar error occurred during Apollo 8, when astronaut Jim Lovell made the same input Lauren had; Hamilton's team corrected the problem within hours, and protection was built into later flights.
She is also credited with popularizing the term "software engineering" — a phrase critics initially found amusing, but one that helped establish software as a discipline in its own right. "I fought to bring the software legitimacy so that it — and those building it — would be given its due respect," she said.
In 2016, President Barack Obama presented Hamilton with the Presidential Medal of Freedom, the nation's highest civilian honor, citing her contributions to concepts including asynchronous software, priority scheduling and priority displays. "Our astronauts didn't have much time, but thankfully they had Margaret Hamilton," Obama said at the ceremony. She also received NASA's Exceptional Space Act Award in 2003.
After leaving MIT in the 1970s, she founded two software companies. She is survived by her daughter, a son-in-law, two grandsons and four great-grandchildren, according to MIT.
What is confirmed: Hamilton died on September 30 at 90, as confirmed by MIT; she led the software development for Apollo's onboard guidance systems; her priority-scheduling software kept the Apollo 11 landing on track during the computer alarms; she received the Presidential Medal of Freedom in 2016.
What remains unknown: The cause of her death has not been disclosed, and the precise trigger of the Apollo 11 guidance computer alarms remains a matter of historical dispute.
What is awaited: No further official details had been released at the time of reporting; any additional statements from MIT, NASA or Hamilton's family would come later.