Margaret Hamilton, Whose Software Saved the Apollo 11 Landing, Dies at 90

She led the MIT team behind Apollo's onboard flight software and coined the term "software engineering."

As the Eagle lunar module dropped toward the moon, its computer began flashing alarms, and Mission Control weighed calling off the landing. The software, Ars Technica recounted, had been built for that moment: it was swamped, so it dropped the jobs that could wait and kept the ones the landing couldn't do without.

Margaret Hamilton, who led the MIT team that wrote Apollo's onboard flight software and coined the term "software engineering," died Sept. 30 in a Cambridge, Massachusetts, hospital. She was 90. Her daughter, Lauren Hamilton, confirmed the death to The Associated Press on Thursday, and NASA Administrator Jared Isaacman credited Hamilton's work on X with helping make the first crewed trips to the moon possible, the AP reported.

The alarm was a 1202 code. A faulty hardware switch had overloaded the computer, MIT said in its obituary Wednesday, and Hamilton's priority-driven design shut down background work so the critical tasks kept running. Houston trusted it and let the descent go on.

Hamilton laid out what happened in a 1971 letter quoted by Ars Technica: the computer knew it was being handed too much, threw out the lower-priority work and restarted what mattered. Without that recovery, she wrote, "I doubt if Apollo 11 would have been the successful Moon landing it was."

The habit of planning for mistakes had an early test case at home. Hamilton often brought Lauren, then 4, to the lab on nights and weekends, and the girl, playing astronaut in the command module simulator, kicked off a pre-launch program called P01 in the middle of a flight. The simulator crashed.

Hamilton proposed a software guard against it and was overruled, according to MIT, on the grounds that trained astronauts would never make that mistake. On Apollo 8, astronaut Jim Lovell did, and the spacecraft's navigation data vanished. Her team was called in to fix it, her change went into the program afterward, and she took to calling it the "Lauren bug."

She'd backed into computing. After a math degree from Earlham College, Hamilton took a job at MIT programming weather simulations for Edward Lorenz, a meteorology professor, work that fed his later papers on chaos theory. Neither of them knew how to program, Ars Technica reported; she once skipped a slow debugging step by unrolling paper tape down a hallway and fixing the binary with a pencil.

In 1965, as she was getting ready for graduate school, her husband spotted a newspaper ad: MIT's Instrumentation Lab, which held NASA's contract for Apollo's onboard software, needed programmers. She was the first one it hired for the project, and its first woman. By 1968 she ran the command and service module team as an assistant director, and the Apollo software effort had grown past 400 people, MIT said.

The name of her field was hers, too. She started saying "software engineering" so the work, and the people doing it, would get the respect hardware got. "When I first started using this phrase, it was considered to be quite amusing," she told the Spanish newspaper El País, as quoted by MIT.

She stayed on after the lab spun off from MIT as Draper Laboratory, then in 1976 founded Higher Order Software, built around preventing errors before they happen. Her second company, Hamilton Technologies, made the Universal Systems Language its main product, a method for designing complex systems with the same defensive streak.

Fame came late, carried by a 1969 photo of her beside a stack of Apollo code listings about as tall as she was. President Barack Obama gave her the Presidential Medal of Freedom in 2016. For the landing's 50th anniversary in 2019, Google tilted more than 100,000 mirrors at a solar farm it runs in the Mojave Desert until they formed her portrait in reflected moonlight, Ars Technica reported.

She's survived by Lauren, a son-in-law, two grandsons, four great-grandchildren and three siblings. MIT said a memorial service is planned for spring in Cambridge.

Lauren Hamilton, the 4-year-old who once crashed the simulator, told the AP her mother ran into plenty of sexism in her field and never answered it with aggression. "She would disarm people with her sense of humor or … just kind of dominate quietly," she said.

Source: arstechnica.com, retrieved October 9, 2026. Other sources: abc7chicago.com, news.mit.edu.