It is thanks to a woman that Man was able to walk on the Moon. Long unknown, Margaret Hamilton was the source leading to the success of the Apollo 11 mission, but also to the development of computer software.

Without her, Neil Amstrong and Buzz Aldrin probably would not have walked on the moon. Her name remained unknown for a long time; however, the United States government rewarded Margaret Hamilton for her services 47 years later. By helping to develop Apollo 11 mission software, she laid the foundation for what modern computing will be like.

Born on August 17, 1936 in Indiana, Margaret Hamilton was passionate about numbers after high school. In 1958, she graduated in mathematics. She readily supported her husband as he graduated from Harvard Law School.

The initial plan was to support her husband for 3 years until he graduated and then he would return the same support for her, so that she could devote herself to study basic mathematics. In 1960, when she was only 24-years-old, Margaret Hamilton took a position at MIT to develop weather prediction software and discovered a new passion. As early as 1961, she worked for the SAGE Project, one of the first missile defense computer systems. Hamilton said, “What they used to do when you came into this organization as a beginner, was to assign you this program which nobody was able to ever figure out or get to run. When I was the beginner they gave it to me as well. And what had happened was it was tricky programming, and the person who wrote it took delight in the fact that all of his comments were in Greek and Latin. So I was assigned this program and I actually got it to work. It even printed out its answers in Latin and Greek. I was the first one to get it to work.”

Margaret Hamilton’s skills and ability to overcome this program made her an ideal candidate for the NASA developer role. In 1963, she was recruited by MIT’s Charles Stark Draper Laboratory, which was responsible for managing the software embedded in NASA’s Apollo program.

A great leap for humanity

Margaret Hamilton was then in charge of designing the embedded system for the Apollo program. She was so passionate about her work that during her long hours of programming, she did not hesitate to take her daughter to her office. Her daughter sometimes played with the simulations created by her mother, while the latter programs the routine software that was to be used by the Apollo module.

She described, “I remember taking my daughter with me at night and on weekends. Once, she started playing astronaut and suddenly the simulation system crashed. I realized that she had selected PO1 – the landing program – during the flight. I started to worry and think what would happen if the astronauts did what she just did? I went to management and told them that changes needed to be made to the program. They said, “It will never happen, our astronauts are very well trained, they don’t make mistakes. On the next mission, Apollo 8, the same thing happened. PO1 was selected in full flight.”

Thanks to Hamilton and her team, the navigation data could be returned in time to the Apollo 8 module and its trajectory was corrected. The young programmer continued to develop her software on Apollo programs. In particular, she succeeded in creating a system for prioritizing tasks that would prove vital to the Apollo 11 mission. On July 21, 1969, when the module was about to land, numerous alarms were triggered: the on-board computer was overloaded and unable to process all the data at the same time, as Margaret Hamilton recounted in a letter in March 1971:

The computer (or rather the software in it) was smart enough to recognize that it was being asked to perform more tasks than it should be performing. It then sent out an alarm, which meant to the astronaut, I’m overloaded with more tasks than I should be doing at this time and I’m going to keep only the more important tasks; i.e., the ones needed for landing … Actually, the computer was programmed to do more than recognize error conditions. A complete set of recovery programs was incorporated into the software. The software’s action, in this case, was to eliminate lower priority tasks and re-establish the more important ones … If the computer hadn’t recognized this problem and taken recovery action, I doubt if Apollo 11 would have been the successful moon landing it was.

After MIT, Margaret co-founded her own software development company, Higher Order Software, and in 1986, Hamilton Technologies, where she developed her own programming language.

In 2003, 27 years after she left NASA, the space agency finally awarded her an “Exceptional Space Act Award” for all her scientific and technical contributions to the Apollo program. Dr. Paul Corto, who nominated her for the award, said he was “surprised to discover that she had never been officially recognized for her pioneering work.” Margaret Hamilton create the foundations of what modern computing is.

A few years later, in 2017, she received the Presidential Medal of Freedom, awarded by Barack Obama, the highest distinction in the United States.