The software that sent humans to the Moon – Matt Porter & Margaret Hamilton

The software that sent humans to the Moon – Matt Porter & Margaret Hamilton


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.

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