Margaret Hamilton, the pioneering computer scientist whose software was critical to the success of the Apollo 11 moon landing, died on September 30 in Cambridge, Massachusetts. She was 90. Hamilton’s death was confirmed by her family and her former employer, the Massachusetts Institute of Technology (MIT), where she developed the groundbreaking software for NASA’s lunar missions.

Hamilton led a team of approximately 100 engineers and programmers who wrote the onboard flight software for the Apollo program. This software guided astronauts Neil Armstrong and Buzz Aldrin safely to the lunar surface on July 20, 1969, and was also integral to subsequent Apollo missions. At a time when computing resources were extremely limited—the Apollo Guidance Computer had only 72 kilobytes of read-only memory and 4 kilobytes of random access memory—Hamilton’s work was considered revolutionary for its reliability and sophistication.

Her software’s capabilities were put to a crucial test during Apollo 11’s landing when the spacecraft’s onboard computer triggered multiple alarms indicating it was overloaded. The cause was a radar left in the wrong mode, which led the computer to temporarily exceed its processing capacity. Hamilton’s program, however, was designed to recognize such conditions and prioritize essential landing tasks by suspending lower-priority processes. This real-time error detection and recovery allowed the mission to proceed rather than abort, ensuring the lunar module’s safe touchdown in the Sea of Tranquility.

Hamilton’s role extended beyond programming; she is credited with popularizing the term “software engineering” to describe the emerging discipline of software development, elevating it to a professional status akin to hardware engineering. She was the first woman hired to work on the Apollo software team at MIT’s Instrumentation Laboratory in 1965 and rose to become director of software engineering for the project.

Before joining the Apollo program, Hamilton worked on the SAGE air defense system for the U.S. Air Force, where she demonstrated her knack for solving complex programming challenges. After the Apollo missions, she contributed to software development for Skylab, America’s first space station, and the early space shuttle designs. In 1976, she founded her own software companies, including Hamilton Technologies, which developed new approaches to error prevention in software systems.

Despite her pivotal contributions, Hamilton remained relatively unknown to the public until recent decades when her work gained wider recognition. In 2016, she was awarded the Presidential Medal of Freedom by then-President Barack Obama, who praised her as an emblem of the many unsung women behind America’s space achievements. A photograph of Hamilton standing beside a towering stack of printed Apollo code became iconic, inspiring a Lego figurine in a Women of NASA series released in 2017.

Hamilton is survived by her daughter, Lauren, two grandsons, four great-grandchildren, and siblings. Her legacy as a trailblazer in software engineering and as a key figure in one of humanity’s greatest scientific achievements endures.