NASA, in its drive to get humans to the lunar surface, was a rather white organization doing manly things. It wasn’t going to put women into space, by any means. John Glenn once said, “the men go off and fight the wars and fly the airplanes and come back and help design and build and test them.”
But despite the macho culture, behind the scenes - and particularly with contractors, women were making the Apollo missions possible. And without one woman, Margaret Hamilton, the Apollo missions would have been impossible.
The Mercury missions were simple missions - a rocket lifted a glorified Javex bottle with a single occupant onto a ballistic trajectory, and they came back down. Sometimes they orbited a few times, but they were piloted craft, and the pilots knew that they had to fire rockets to slow them down at a precise time for a precise duration. If they did that, they’d get back down in the right spot where they could be scooped from the water by a naval vessel.
The Gemini missions required something more - a guidance computer. The Gemini capsules were the proving ground for the Apollo program: showing that a spacecraft could dock and perform complex maneuvers. But the Gemini computers were still not used extensively, and the pilots were mostly flying by the seat of their pants (as Neil Armstrong did when he rescued one of his missions from a crazy spin.)
When Apollo came along, they had to do something else entirely. No rough splashdown here - on a body with no atmosphere, they had to take a spindly legged lander from thousands of miles an hour down to a soft touchdown - from descent engine ignition to engine cutoff was about 15 minutes. The attention to detail would require a true guidance computer.
The Apollo Guidance computer was a radical new device: unlike Earth computers of the time, it wasn’t a timeshare. It was a small limited memory device that would interact directly with input and display hardware - a number pad to enter commands, and an LED display to give you results. It would be connected to all of the ship’s critical systems, taking input from every sensor on the lander as well as radar. And all this on a computer roughly as powerful as a Commodore Pet, or the first Apple computers from the 70s.
In order to handle all of these inputs without failing the astronauts, they needed a sophisticated software team with skills far beyond NASA’s, and so they hired MIT’s Instrumentation Laboratory to develop a sophisticated software program that could handle the enormous needs of the landing on the impoverished specs of the AGC.
MIT assigned as the project lead Margaret Hamilton, who had already developed great expertise in aerospace programming - creating a satellite tracking system and working on SAGE, a system to detect enemy aircraft.
Hamilton developed a system to handle multiple tasks cooperatively (the leanest way to do multitasking), but which could be interrupted by items on something called a “waitlist.” Most important of all, the computer could never hard-crash - anything that pushed the computer too far needed to be handled.
“Looking back, we were the luckiest people in the world. There was no choice but to be pioneers; no time to be beginners,” she told NASA for a retrospective. NASA’s managers had no idea what any of this software stuff was or how it worked, so they gave Hamilton and her team complete control.
The first test for her team was Apollo 8. They had devised programs for the command module, and though this mission had no lander, it would go to the moon. The mission was a complete success.
Apollo 10 would test the lander: Apollo 10’s descent stage did not go all the way to the lunar surface, but did implement most of the descent, and gave the Apollo Guidance Computer a good solid test.
The report that MIT prepared for NASA after the Apollo 10 mission concluded they were ready.
An extremely complex array of measurement and processing equipment has been designed for the extraordinarily complex and difficult task of supporting the manned lunar landing.- These have been tested extensively now in an operational environment and have been demonstrated to be fully ready to help a crew of astronauts land on the moon.
Hamilton and team had done it - but they were to be tested once more before men walked on the moon.
As Apollo 11’s Eagle descended to the surface, the computer started emitting the message “1202” - Armstrong reported this back to NASA, with no idea what it was. The CapCom told him to ignore it.
Behind the scenes, a radar system designed to keep track of the command module was flooding the computer with data. The AGC was supposed to be at 85% usage - the radar data was taking it past 100%.
But Hamilton and her team had anticipated everything. If the system was being overloaded (which is what 1201 and 1202 were alerting the astronauts to), she had designed the computers to reboot, and then pick up the critical tasks it was doing before, at exactly the point it was doing them. It was masterful design, often credited as the birth of “software engineering” and reliable computing.
None of this takes away from Armstrong’s masterful flying - at the last moment he saw that the lander was coming down on a field of boulders and manually flew away from it with seconds of fuel to spare.
But man never would have made it to the surface of the moon without woman - Margaret Hamilton - on the job.