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Remembering the Apollo 11 Moon Landing With the Woman Who Made It Happen

5 minute read

It was on this day, July 20, in 1969, that the Apollo 11 astronauts reached the moon and Neil Armstrong took his famous small step. People celebrated the world over, though few were more relieved than Margaret Hamilton.

“I remember thinking, Oh my God, it worked,” the pioneering software engineer tells TIME. “I was so happy. But I was more happy about it working than about the fact that we landed.”

The “it” that worked was Apollo 11’s on-board flight software, which Hamilton, as part of the MIT team working with NASA, led the effort to build. There was no guarantee things would play out so smoothly. In fact, just before the lunar landing was supposed to happen, alarms went off indicating that there wasn’t enough room on the computer for the landing software to work effectively. Turns out a radar was sending unnecessary data to the computer, overloading it with superfluous information.

The work that Hamilton had done helped enable the computer to figure out which of the multiple processes it had to do was most important. “It got rid of the lesser priority jobs and kept the higher priority jobs, which included the landing functions,” she explains.

That fix gave NASA the confidence to go ahead with the historic moon landing.

Hamilton was later given NASA’s Exceptional Space Act Award for her work on those Apollo systems. (She’s also credited with coining the term “software engineering.”) That she was successful in the pre-women’s lib era in a field that remains tough for women to crack has helped revive interest in her career: Hamilton achieved a sort of Internet fame recently when the photo above made the rounds.

Hamilton says that she was so wrapped up in her work that she didn’t notice the gender problems of the time until Mad Men came around and seemed a little too familiar. (Even if gender wasn’t uppermost in her mind, she did advance that cause too: Hamilton recalls that a woman on her team was told by the MIT credit union that she couldn’t get a loan without her husband’s signature, though male applicants didn’t need spousal approval. Hamilton complained about the policy and had it changed. “It was the culture, but I won, and I was so happy,” she recalls. “I didn’t do it because of male versus female; I was very conscious of what was fair and what wasn’t fair.”)

Part of what had made Hamilton’s work so effective was that she tested everything so rigorously, in a simulator that could demonstrate the “system of systems” at work, and the relationship between the software, the hardware and the astronaut. “We couldn’t run something up to the moon,” she says. But they could run lots of tests on the ground. Analyzing the errors that came up during testing, Hamilton’s team found that nearly three-quarters of them were interface errors, like conflicts in timing or priority. Since the computer code was on cards, a software engineer might write code that told the computer how many cards to advance; if someone later added a card in the middle while working on the code, that number would be wrong. Hamilton realized that those problems were avoidable.

“We’ve been working on this ever since Apollo—or starting with Apollo, I should say,” she says. “I’ve been on a mission in its own right, working with this Universal Systems Language, which allows you to get things up front. It’s kind of like a root canal: you waited till the end, [but] there are things you could have done beforehand. It’s like preventative healthcare, but it’s preventative software.”

She founded Hamilton Technologies Inc. in 1986, where she has continued her work with Universal Systems Language.

In 1969, TIME’s special report on the moon landing included the optimistic prediction that Mars would be up next, and soon (“as early as 1982”). Software reliability may not have much romantic appeal, but Hamilton believes it is key to future exploration of the universe, including Mars. Which makes sense, since reliable software saves money. Testing is expensive, so it’s cheaper for NASA (and private space programs) if problems can be caught in advance, thus requiring fewer tests. And cutting down on costly tests means smaller budgets that are more likely to get approved.

Which is something Hamilton is keen to see happen. “I hope,” she says, “that we continue with exploration.”

Read TIME’s special issue from 1969 about the Apollo 11 moon landing: Man on the Moon

‘To the Moon and Back.’ See LIFE’s Complete Special Issue on Apollo 11

Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. July 20, 1969: "Neil Armstrong's booted foot pressed firmly in the lunar soil. . . ."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "In orbit 63 miles high the Lunar Module approaches the landing zone."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "The Eagle has landed."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Buzz Aldrin eased down Eagle's ladder, paused on the last rung and jumped the final three feet."LIFE Magazine
LIFE magazine Special Edition, August 11, 1969. "Aldrin's gold visor mirrored Eagle and Armstrong, who took most of these pictures."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Aldrin walked from the Lunar Module to set up two experimental packages — the laser beam reflector and the seisometer."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Adrin made final adjustments to the seisometer, left behind to monitor possible moon quakes. Earlier he unfurled the 'solar wind sheet,' designed to trap tiny particles hurled from the distant Sun."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Nine hours after his arrival, man had littered the moonscape with his paraphernalia."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "On the windless plain Aldrin saluted the American flag, stiffened with wire so that it would 'wave'. . . ."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Eagle landed 125 feet west of a rock strewn-crater, several feet deep and 80 feet across."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Left: Aldrin inspected the condition of the Lunar Modules footpad. Right: The view from Eagle's window after the walk."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "The simplest mark of man's first visit — footprints in the fine moon sand."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "As seen at some distance from Columbia, Eagle rolled left and closed for rendezvous 69 miles above moon ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Eagle turned its docking port towards Columbia moments before hookup. earth is in upper right corner of large picture ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Tired but triumphant Armstrong got ready for the trip back ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Left:The plaque left behind with the Lunar Module's descent stage. Right: Aldrin, Collins and Armstrong — heroes of history's greatest exploration ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Three kids bound for the moon. From left: Armstrong, Aldrin and Collins ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Neil Armstrong: He could fly before he could drive ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Despite a relentless schedule Armstrong sometimes found moments for normal family life ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Away from work Armstrong enjoyed a few frivolous moments ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Edwin 'Buzz' Aldrin: 'The best scientific mind in space' ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Aldrin is like most astronauts, an exercise buff who spends nearly an hour a day keeping fit ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Aldrin with his wife and daughter ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Mike Collins: An engineer who does not love machines ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Before the moon flight Collins spent time at home with his family ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "Collins with his wife and daughter ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "A Calendar of Space Flight: Man's Countdown for the Moon ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "A Calendar of Space Flight: Man's Countdown for the Moon ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "A Calendar of Space Flight: Man's Countdown for the Moon ..."LIFE Magazine
Neil Armstrong Apollo 11
LIFE magazine Special Edition, August 11, 1969. "A Calendar of Space Flight: Man's Countdown for the Moon ..."LIFE Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "Unlocking the ancient mysteries of the Moon ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "Anatomy of the Lunar Receiving Lab ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "What the Moon Samples Might Tell Us ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "What the Moon Samples Might Tell Us ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "So long to the good old moon ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "So long to the good old moon ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "The dawn of the day man left his planetary cradle. Right: Armstrong led the way from gantry to spacecraft ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "Apollo 11 lifts off ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "Journalists — nearly 3,500 of them from the U.S. and 55 other countries -- watched in hushed expectant awe as Apollo began its slow climb skyward ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "Jan Armstrong raised a hand to ward off the bright morning sun and watched her husband's spacecraft rear toward a rendezvous with the moon ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "At Disneyland (left) hundreds gave up 'moon rides' to watch the real thing. While in Manhattan people cheered and worried in front of huge TV screens. Las Vegas casino crowds paused over Baccarat (below) and passengers jammed a waiting room at JFK airport (right) to watching Armstrong's walk ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "The moonwalk was broadcast live in London (left) and other world capitals, although Moscow viewers (right) had to wait several hours for an edited version. Pope Paul got a telescopic close-up of the moon, while South Koreans clamored around a 20-foot-square TV screen. GIs read of lunar adventure ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "Andy Aldrin watched with grim determination as his father set foot on the moon, while at the Collins home Pat and friends followed the walk on two television sets. Joan Aldrin collapsed on the floor in happy relief when Eagle lifted safely off the moon ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "The fiery sideshow as Apollo comes home ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "The capsule was first righted by floatation bags. Then as astronauts in special insulation suits watched, frogmen scrubbed it down with disinfectant. (right). Apollo crew waved as they entered quarantine aboard [the recovery ship] the USS Hornet ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "In Houston the splashdown joy was personal and intense. NASA workers leaped from their consoles waving flags, and at home Jan Armstrong (below left) beamed and sighed in relief. Joan Aldrin applauded as Buzz Aldrin struggled into the raft and Pat Collins served champagne to a house full of happy friends ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "Armstrong, Collins and Aldrin grinned jubilantly from inside their quarantine chamber on the carrier Hornet before their flight home to Houston ..."Life Magazine
Neil Armstrong Apollo 11
Life magazine Special Edition, August 11, 1969. "That's one small step for a man, one giant leap for mankind ..."Life Magazine

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Write to Lily Rothman at lily.rothman@time.com