Margaret Elaine Hamilton (née Heafield; born August 17, 1936) is an American computer scientist. She directed the Software Engineering Division at the MIT Instrumentation Laboratory, where she led the development of the on-board flight software for NASA's Apollo Guidance Computer for the Apollo program. She later founded two software companies, Higher Order Software in 1976 and Hamilton Technologies in 1986, both in Cambridge, Massachusetts.
Hamilton has published more than 130 papers, proceedings, and reports, about sixty projects, and six major programs. She coined the term "software engineering", stating, "I began to use the term 'software engineering' to distinguish it from hardware and other kinds of engineering, yet treat each type of engineering as part of the overall systems engineering process."
On November 22, 2016, Hamilton received the Presidential Medal of Freedom from President Barack Obama for her work leading to the development of on-board flight software for NASA's Apollo Moon missions.
Margaret Elaine Heafield was born August 17, 1936, in Paoli, Indiana, to Kenneth Heafield and Ruth Esther Heafield (née Partington). The family later moved to Michigan, where Margaret graduated from Hancock High School in 1954.
She studied mathematics at the University of Michigan in 1955 before transferring to Earlham College, where her mother had been a student. She earned a BA in mathematics with a minor in philosophy in 1958. She cites Florence Long, the head of the math department at Earlham, as helping with her desire to pursue abstract mathematics and become a mathematics professor.
She says her poet father and headmaster grandfather inspired her to include a minor in philosophy in her studies.
In Boston, Hamilton initially intended to enroll in graduate study in abstract mathematics at Brandeis University. However, in mid-1959, Hamilton began working for Edward Norton Lorenz, in the meteorology department at Massachusetts Institute of Technology (MIT). She developed software for predicting weather, programming on the LGP-30 and the PDP-1 computers at Marvin Minsky's Project MAC. Her work contributed to Lorenz's future publications on chaos theory, as acknowledged by Lorenz himself. At the time, computer science and software engineering were not yet established disciplines; instead, programmers learned on the job with hands-on experience. She moved on to another project in the summer of 1961, and hired and trained Ellen Fetter as her replacement.
From 1961 to 1963, Hamilton worked on the Semi-Automatic Ground Environment (SAGE) Project at the MIT Lincoln Lab, where she was one of the programmers who wrote software for the prototype AN/FSQ-7 computer (the XD-1), used by the U.S. Air Force to search for possibly unfriendly aircraft. She also wrote software for a satellite tracking project at the Air Force Cambridge Research Laboratories. The SAGE Project was an extension of Project Whirlwind, started by MIT to create a computer system that could predict weather systems and track their movements using simulators. SAGE was soon developed for military use in anti-aircraft air defense. 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.
It was her efforts on this project that made her a candidate for the position at NASA as the lead developer for Apollo flight software.
MIT Instrumentation Laboratory and the Apollo Guidance Computer
Hamilton learned of the Apollo project in 1965 and wanted to get involved due to it being "very exciting" as a Moon program. She joined the MIT Instrumentation Laboratory, which developed the Apollo Guidance Computer for the Apollo lunar exploration program. Hamilton was not the first programmer hired for the Apollo project at MIT (despite ), because she joined several years after the project started in 1961. Hamilton was the first female programmer in the project, and later became Director of the Software Engineering Division. She was responsible for the team writing and testing all onboard in-flight software for the Apollo spacecraft's Command and Lunar Module and for the subsequent Skylab space station. Another part of her team designed and developed the systems software. This included error detection and recovery software such as restarts and the Display Interface Routines (also known as the Priority Displays), which Hamilton designed and developed. She worked to gain hands-on experience during a time when computer science courses were uncommon and software engineering courses did not exist.
In one of the critical moments of the Apollo 11 mission, the Apollo Guidance Computer, together with the on-board flight software, averted an abort of the landing on the Moon. Three minutes before the lunar lander reached the Moon's surface, several computer alarms were triggered. According to software engineer Robert Wills, Buzz Aldrin entered the codes to request that the computer display altitude and other data on the computer's screen. The system was designed to support seven simultaneous programs running, but Aldrin's request was the eighth. This action was something he requested many times while working in the simulator. The result was a series of unexpected error codes during the live descent. The on-board flight software captured these alarms with the "never supposed to happen displays" interrupting the astronauts with priority alarm displays.
Hamilton had prepared for just this situation years before:
There was one other failsafe that Hamilton likes to remember. Her "priority display" innovation had created a knock-on risk that astronaut and computer would slip out of sync just when it mattered most. As the alarms went off and priority displays replaced normal ones, the actual switchover to new programmes behind the screens was happening "a step slower" than it would today.
Hamilton had thought long and hard about this. It meant that if Aldrin, say, hit a button on the priority display too quickly, he might still get a "normal" response. Her solution: when you see a priority display, first count to
By some accounts, the astronauts had inadvertently left the rendezvous radar switch on, causing these alarms to be triggered (the claim that the radar was left on inadvertently by the astronauts is disputed by Robert Wills with the National Museum of Computing). The computer was overloaded with interrupts caused by incorrectly phased power supplied to the lander's rendezvous radar. The program alarms indicated "executive overflows", meaning the guidance computer could not complete all of its tasks in real time and had to postpone some of them. The asynchronous executive designed by J. Halcombe Laning was used by Hamilton's team to develop asynchronous flight software:
Because of the flight software's system-software's error detection and recovery techniques that included its system-wide "kill and recompute" from a "safe place" restart approach to its snapshot and rollback techniques, the Display Interface Routines (AKA the priority displays) together with its man-in-the-loop capabilities were able to be created in order to have the capability to interrupt the astronauts' normal mission displays with priority displays of critical alarms in case of an emergency. This depended on our assigning a unique priority to every process in the software in order to ensure that all of its events would take place in the correct order and at the right time relative to everything else that was going on.