At roughly 4pm on July 20, 1969, mankind was just minutes away  from landing on the surface of the moon. But before the astronauts  began their final descent, an emergency alarm lit up. Something was overloading  the computer, and threatened to abort the landing. Back on Earth, Margaret Hamilton  held her breath. She'd led the team developing  the pioneering in-flight software, so she knew this mission  had no room for error. But the nature  of this last-second emergency would soon prove her software  was working exactly as planned. Born 33 years earlier in Paoli, Indiana,  Hamilton had always been inquisitive. In college, she studied mathematics and philosophy, before taking a research position at the  Massachusetts Institute of Technology to pay for grad school. Here, she encountered her first computer while developing software to support research  into the new field of chaos theory. Next at MIT's Lincoln Laboratory, Hamilton developed software  for America’s first air defense system to search for enemy aircraft. But when she heard  that renowned engineer Charles Draper was looking for help  sending mankind to the moon, she immediately joined his team. NASA looked to Draper and his group  of over 400 engineers to invent the first compact  digital flight computer, the Apollo Guidance Computer. Using input from astronauts, this device would be responsible  for guiding, navigating and controlling the spacecraft. At a time when unreliable computers  filled entire rooms, the AGC needed to operate  without any errors, and fit in one cubic foot of space. Draper divided the lab into two teams, one for designing hardware  and one for developing software. Hamilton led the team that built  the on-board flight software for both the Command and Lunar Modules. This work, for which she coined the term “software engineering," was incredibly high stakes. Human lives were on the line,  so every program had to be perfect. Margaret’s software needed to quickly detect unexpected errors and recover from them in real time. But this kind of adaptable program  was difficult to build, since early software could only process  jobs in a predetermined order. To solve this problem, Margaret designed her program  to be “asynchronous,” meaning the software's more important jobs would interrupt less important ones. Her team assigned every task  a unique priority to ensure that each job  occurred in the correct order and at the right time— regardless of any surprises. After this breakthrough, Margaret realized her software  could help the astronauts work in an asynchronous environment as well. She designed Priority Displays that would interrupt  astronaut’s regularly scheduled tasks to warn them of emergencies. The astronaut could then communicate with Mission Control to determine the best path forward. This marked the first time flight software communicated directly— and asynchronously—  with a pilot. It was these fail safes that triggered  the alarms just before the lunar landing. Buzz Aldrin quickly realized his mistake— he’d inadvertently flipped  the rendezvous radar switch. This radar would be essential  on their journey home, but here it was using up  vital computational resources. Fortunately, the Apollo Guidance Computer was well equipped to manage this. During the overload,  the software restart programs allowed only the highest priority jobs  to be processed— including the programs  necessary for landing. The Priority Displays  gave the astronauts a choice— to land or not to land. With minutes to spare,  Mission Control gave the order. The Apollo 11 landing was about  the astronauts, Mission Control, software and hardware all working together as an integrated system of systems. Hamilton’s contributions were essential to the work of engineers and scientists inspired by President John F. Kennedy’s  goal to reach the Moon. And her life-saving work  went far beyond Apollo 11— no bugs were ever found in the in-flight software for any crewed Apollo missions. After her work on Apollo, Hamilton founded a company that uses  its unique universal systems language to create breakthroughs  for systems and software. In 2003, NASA honored her achievements  with the largest financial award they’d ever given to an individual. And 47 years after her software first guided astronauts to the moon, Hamilton was awarded  the Presidential Medal of Freedom for changing the way we think  about technology.