Margaret Hamilton (1936–2026), Juliette Pagacz

Black-and-white portrait of Margaret Hamilton against a dark background, her head slightly tilted. — Margaret Hamilton, 1995. Photograph by Daphne Weld Nichols (Wikimedia Commons, CC BY-SA 3.0).

Margaret Hamilton died on 30 September, at 90.

She led the team at the MIT Instrumentation Laboratory that designed the on-board flight software for the Apollo missions, including Apollo 11, the first crewed Moon landing. By 1968, more than 400 people were working on that software. A pioneer in an overwhelmingly male field, she actually began calling the work “software engineering” so that it would be taken as seriously as hardware. At first, the phrase was treated as a joke.

The software was written in assembly language. It is a very low-level language, “close to the metal”: each instruction corresponds almost directly to a basic operation of the processor. It gives precise control over the machine, but it is slow and difficult to write.

Today, in a language like Python, you would write:

if altitude < 100:    # if the altitude is below 100
    alarm = 1         # then switch the alarm on

In assembly (simplified here), the same thing becomes:

        LOAD  R1, [altitude]   ; copy the value stored at "altitude" into register R1
        LOAD  R2, #100         ; put the number 100 into register R2
        CMP   R1, R2           ; compare R1 and R2
        JGE   NEXT             ; if R1 >= R2, jump to NEXT (no alarm)
        LOAD  R3, #1           ; otherwise, put 1 into register R3
        STORE R3, [alarm]      ; and store it at "alarm"
NEXT:   ...                    ; the program carries on here

On 20 July 1969, a few minutes before touchdown, the onboard computer was given more work than it could handle. At the time, an overloaded computer simply froze (it still happens), and the landing would probably have been called off. But the system Hamilton and her team had designed knew what was vital and what could wait. It dropped the secondary tasks and kept guiding the descent. Shortly afterwards, Neil Armstrong and Buzz Aldrin were on the Moon.

“There was no second chance,” she said of Apollo. Her answer was to build software that expects things to go wrong and keeps doing what matters anyway. That idea now runs through the systems our lives depend on: planes, cars, medical devices.

I don't usually write about the passing of famous figures. But when I was learning computer science, there were about seventy students, and maybe five women? I didn't grow up with many female role models, and certainly not from the scientific world; Hamilton could have been one. And I do wonder what it would have changed to know, in my little girl's mind, that the code that landed people on the Moon was written by a team led by a young woman.

Also, my CS classroom was not an exception. In the United States, women earned 37% of computer science degrees in 1984. Today it is around a fifth.

That is why, since I started teaching new technologies and programming, I've always made sure to tell my students about the women who pioneered the field.

MIT News obituary: “Margaret Hamilton, computing pioneer who led software development for the Apollo program, dies at 90” (7 October 2026).