The machine that made lunar missions possible

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We've all been there: you're working on something important, your PC crashes and you lose all your progress.

Such a failure was not an option during Apollo missions, the first time ever that a computer had been tasked with managing flight control and life support systems – and therefore the lives of astronauts on board.

Despite a notorious false alarm during the lunar descent that sent out commander Neil Armstrong's heartbeat, it was a resounding success that laid the foundation for everything from modern avionics to multitasking operating systems.

Here are some of the ways in which the Apollo Guidance Computer (AGC), millions of times less powerful than a 2019 smartphone, has shaped the world we live in today:

– Microchip revolution –

Integrated circuits or microchips were a necessary part of the miniaturization process that allowed ...

Integrated circuits, or microchips, were a necessary part of the miniaturization process that allowed computers to be placed on board spacecraft, in contrast to the technology of the giant vacuum tube, power-hungry that came before

HO, Smithsonian National Air and Space Museum / AFP

Integrated circuits, or microchips, were a necessary part of the miniaturization process that allowed computers to be placed on board spacecraft, in contrast to the giant, power-hungry vacuum tube technology that came before.

The credit for their invention goes to Jack Kilby of Texas Instruments and Robert Noyce, who co-founded Fairchild Semiconductor and later Intel in Mountain View, California.

But NASA and the Department of Defense – which needed microchips to drive the Minuteman ballistic missiles aimed at the Soviet Union – greatly accelerated their development by producing the demand that facilitated mass production.

"They had these incredible, absolutely crazy reliability requirements that nobody could ever imagine," said Frank O & # 39; Brien, historian of the spaceflo and author of "The Apollo Guidance Computer: Architecture and Operation".

At the beginning of the 60s, the two agencies bought almost all the microchips produced in the United States, about one million all told, added O & # 39; Brien, forcing the producers to improve their projects and build circuits that lasted longer than their first life cycles of just a few hours.

– Multitasking –

Margaret Hamilton led the team that programmed Apollo's flight computer; their code allowed ...

Margaret Hamilton led the team that programmed Apollo's flight computer; their code allowed the machine to give priority to crucial tasks over non-essential ones

HO, Smithsonian National Air and Space Museum / AFP

Modern computers, like the smartphone in your pocket, are generally able to perform a myriad of tasks simultaneously: management of e-mails in one window, a GPS map in another, various social network apps, all set for incoming calls and messages.

But in the first era of computers, we thought of them in a fundamentally different way.

"They were not asked to do much, they were asked to reduce the numbers and replace the humans who would have made them with mechanical addition machines," said Seamus Tuohy, the chief director of space systems at Draper, who has moved away from the MIT Instrumentation Laboratory which developed the Apollo Guidance Computer.

All this changed with Apollo Guidance Computer, a machine the size of a briefcase that had to juggle a series of vital tasks, from navigating the ship to operating its oxygen generator, its heaters and carbon dioxide systems.

Instead of a computer operator providing a machine with a series of calculations and leaving it for hours or even days to process the answer, all this must be done in a time-sensitive way, with cut-offs and user capacity (astronauts) to give him commands in real time.

NASA has deemed it necessary to have an on-board computer to handle all these functions in case the Soviets tried to block radio communications between the ground control in Houston and US spaceships and why Apollo was originally designed to penetrate deeper. in the solar system.

All this required a "software" architecture, largely designed by the engineer Hal Laning.

– Real-time input –

"The way the computer managed the overhead was a real step forward," said Paul Ceruzzi, a Smithsonian Institution researcher on aerospace electronics

Issam AHMED, AFP Photo

He also needed new ways of interacting with the machine that went beyond the programming of punched cards of the time.

Engineers have identified three main ways: the switches that are still found in modern cockpits, a hand controller connected to the world's first digital fly-by-wire system and a "display and keyboard" unit, abbreviated DSKY (pronounced "off-key").

Astronauts entered two-digit codes for verbs and nouns, to execute commands such as propulsion shots or to cling to a particular star if the ship, which relied on an inertial guidance system to maintain pitch, roll and yaw, he had started slipping off course.

O & # 39; Brien used the metaphor of a tourist who visits the United States and is hungry but does not know much the English and could say "Eat pizza" to convey the fundamental meaning.

– Passing the test –

The most tense moment of Apollo 11 came during the last minutes of his descent to the lunar surface, when the computer's alarm bells began to ring and made it look as if it had crashed.

Such an event could have been catastrophic, forcing the crew to abort their mission or even send the ship spiraling out of control to the surface.

Back in Houston, an engineer realized that while the machine was temporarily overloaded, his intelligent programming allowed him to automatically eliminate less important tasks and concentrate on landing.

"The way the computer handled the overhead was a real breakthrough," said Paul Ceruzzi, a Smithsonian Institution scholar on aerospace electronics.

O & # 39; Brien noted that while the AGC was meager compared to modern computing standards, with a clock speed of 1 Mhz and a total of 38Kb of memory, such comparisons have denied its true caliber.

"With that terribly small capacity, they were able to do all the extraordinary things that we now consider completely normal," he said.

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