She Wrote The Code For The Moon landing In 1969

This is a great photo of Margaret Hamilton who worked on the Apollo program in the sixties. Margaret Hamilton was the lead software engineer for Project Apollo in an era when we used slide rules only.

It had long been tradition that operating calculating machines was “women’s work”; it was thought to be just keypunching, like typing. Women programmed and operated the punchcard machines to produce calculations for the Manhattan Project.

Margaret Hamilton, lead software engineer of the Apollo Project, stands next to the code she wrote by hand and that was used to take humanity to the moon, 1969.

Despite the tendency of the project physicists to minimize their contribution, this was demanding work, much more than just moving cards from slot to slot.

 They were usually given requirements from the tech people, but often designed the approach and set up the calculations themselves.

The bias that “women do the mere programming” extended into the early days of the computer, and it meant that many of the earliest and most pioneering programmers were women, learning hands-on to do things that had never been done before.

We all know about Amazing Grace Hopper, who wrote the first compiler.

Margaret Hamilton earned her BA in math from Earlham College, but obviously learned about programming on the job—there was no other way.

In the photo above, she is standing in front of the printouts of the code for the Apollo guidance system, a lot of which she wrote and which she oversaw.

She was all of 31 when the Apollo 11 lunar module landed on the moon, running her code. Apollo 11 was able to land at all only because she designed the software robustly enough to handle buffer overflows and cycle-stealing.)

She’s now a tech CEO and won the ‘86 Lovelace Award and the NASA Exceptional Space Act Award. The engineers weren’t all boys with crewcuts, short sleeve oxford shirts, and narrow black ties. That’s just a fairy tale they told for a while.

Something to remember. I suppose today’s kids are ho-hum about these recoveries of memory, but I think they’re pretty neat.

Apollo 11 Moon Landing

Hamilton’s work prevented an abort of the Apollo 11 Moon landing. Three minutes before the Lunar lander reached the Moon’s surface, several computer alarms were triggered. The computer was overloaded with incoming data, because the rendezvous radar system (not necessary for landing) updated an involuntary counter in the computer, which stole cycles from the computer.

Due to its robust architecture, the computer was able to keep running; the Apollo onboard flight software was developed using an asynchronous executive so that higher priority jobs (important for landing) could interrupt lower priority jobs. The fault was attributed to a faulty checklist and the radar being erroneously activated by the crew.

Due to an error in the checklist manual, the rendezvous radar switch was placed in the wrong position. This caused it to send erroneous signals to the computer. The result was that the computer was being asked to perform all of its normal functions for landing while receiving an extra load of spurious data which used up 15% of its time.

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.


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