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Space History: The Brilliant, Funny Computer Code Behind the Apollo 11 Mission

From their key positions in this control center at Goddard, the Manned Space Flight Network operations director and staff controlled Apollo mission communications activities throughout a far-flung worldwide complex of stations. Image Credit: NASA’s Goddard Space Flight Center.

The code was written in the late ’60s by Margaret Hamilton and her team at the Massachusetts Institute of Technology Instrumentation Laboratory for the Apollo Guidance Computer.

Paul Smith writes: NASA’s Apollo 11 mission—the mission that put human beings on the moon for the first time—was launched in 1969, the year after I was born. My early Christmas presents were giant kids’ books full of pictures of that giant Saturn V rocket launching into space, the command and lunar modules, and of guys in bulky space suits walking on the moon. The first intelligible answer I gave to the question, “What do you want to be when you grow up?” was, “Astronaut.”

gemini-mission-control

I did not end up becoming an astronaut.

Computers also captured my attention at an early age, and now I work as a developer for Slate. But my fascination with space endures—so needless to say, I was pretty excited when I heard that the source code for Apollo 11’s computer guidance systems was uploaded on July 8 to Github, a popular site used by programmers to share code and collaboratively build software. Anyone can now read the actual lines of programming code used to land men on the moon.

[Read the full story here, at slate.com]

The code was written in the late ’60s by Margaret Hamilton and her team at the Massachusetts Institute of Technology Instrumentation Laboratory for the Apollo Guidance Computer.

“I have no idea what a DVTOTAL is, but I’m pretty sure that by BURNBABY, they mean ‘launch a 300-foot rocket ship into space.’ And how totally and completely freaking awesome is that?”

The code is pretty inscrutable to casual inspection: It’s not written in a programming language recognizable to modern coders. But Hamilton and her team wrote comments in their code (just like I do when I write code for Slate’s website) to help remind them what’s going on in a given spot in the program. Those parts are surprisingly readable. Here’s a block of code from a file called BURN_BABY_BURN–MASTER_IGNITION_ROUTINE.s (really, that’s what it’s called):

Apollo1

So, clearly, “don’t forget to clean out leftover DVTOTAL data when GROUP 4 RESTARTS and then BURN, BABY!” I have no idea what a DVTOTAL is, but I’m pretty sure that by BURNBABY, they mean “launch a 300-foot rocket ship into space.” And how totally and completely freaking awesome is that?

Altogether, with comments and some added copyright headers, the AGC code adds up to about 2 megabytes—a teeny tiny fraction of the amount of code packed into an Apple Watch. You probably downloaded more data in the process of loading this web page. That’s perhaps not surprising, given the limitations of the equipment the code ran on. The Apollo Guidance Computer was miraculously advanced for the late 1960s, able to be used on a very power-, space-, and weight-constrained space ship. Still, it could only run a couple of kilobytes of code at a time…(read more)

Source: slate.com

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