Margaret Hamilton, the pioneering computer scientist whose software helped guide NASA’s Apollo missions, died on September 30, 2026, in Cambridge, Massachusetts. She was 90.

Hamilton joined MIT’s Instrumentation Laboratory in the 1960s and became the first programmer hired for the Apollo project. She eventually led the team responsible for developing the onboard flight software that guided astronauts to the Moon. Her work also helped establish software engineering as a discipline.

One of her most important ideas was “defensive programming”—designing software to anticipate human mistakes and unexpected problems. After her young daughter accidentally crashed an Apollo simulator, Hamilton warned that a similar error could happen during a real mission. Her concerns were initially dismissed, but a similar mistake occurred during Apollo 8, proving her point.

Her software faced its greatest test during Apollo 11 in July 1969. Just before the lunar landing, the onboard computer produced a 1202 alarm, indicating that it was overloaded. Hamilton’s software had been designed to prioritize critical tasks and automatically discard less important ones. Because the system continued handling the essential landing functions, Mission Control allowed the landing to continue. Neil Armstrong and Buzz Aldrin successfully landed on the Moon.

Hamilton later received numerous honors, including the Presidential Medal of Freedom from Barack Obama in 2016. Her famous photograph standing beside the enormous stack of Apollo code helped make her an icon of women in science and technology.

She is survived by her daughter, grandchildren, great-grandchildren and siblings.