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Diskee: Apollo's Most Important Crewmember (paleotronic.com)
62 points by empressplay on Jan 22, 2019 | hide | past | favorite | 18 comments

The DSKY was a demo.

“The DSKY and PINBALL (something flashy with buttons) was a demo. And that demo got us to the moon. "Apparently, nobody had yet arrived at any kind of software requirements for the AGC's user interface when the desire arose within the Instrumentation Laboratory to set up a demo guidance-computer unit with which to impress visitors to the lab. Of course, this demo would have to do something, if it was going to be at all impressive, and to do something it would need some software. In short order, some of the coders threw together a demo program, inventing and using the verb/noun user-interface concept, but without any idea that the verb/noun concept would somehow survive into the flight software. As time passed, and more and more people became familiar with the demo, nobody got around to inventing an improvement for the user interface, so the coders simply built it into the flight software without any specific requirements to do so."


It's funny that the personified user interface is used as the title, because the star of the show is something much more hidden - one of the first multitasking "operating systems" correctly handling, and limiting the impact of, an unforeseen CPU-hungry process in the midst of the first moon landing! The OP's a fascinating read and more technical than the title might imply.

For anyone interested in the process of compiling and loading the code for these systems (available at https://github.com/chrislgarry/Apollo-11/ ) into the "core rope memory" used for program storage in the capsules, here's one of the original spec documents, as well as an image from that document showing what I'd call a "compilation-bureaucracy-pipeline" that's a fascinating glimpse into software deployment practices.



”the DSKY (which they pronounced Diskee), a simple LED and button-based interface”

Wikipedia says there were visible-light LEDs in 1962 (https://en.wikipedia.org/wiki/Light-emitting_diode#Discoveri...), but even ignoring they emitted red light, which the photos do not show, I think it’s unlikely they used them in this device.

https://en.wikipedia.org/wiki/Apollo_Guidance_Computer#DSKY_... claims it used ”green high-voltage electroluminescent seven-segment displays”. That seems more likely to me.

They were indeed EL displays.

Fran Blanche attempted a GoFundMe project to recreate these displays. Unfortunately the project stalled.



This article makes it seem more dramatic and spur-of-the-moment than other writings on the same topic I've read. The Wikipedia article on Jack Garman asserts (unsourced) that they'd generated a 1202 alarm in simulations and Bales had (incorrectly) called for an abort there. So it was actually a rehearsed scenario, with an analyzed "should go anyway" decision.

I read the same thing in Gene Kranz's book Failure Is Not An Option - it should probably be added there as a reference.

If you're interested in the Apollo Guidance Computer there's some really excellent material out there in the world to learn more. My two favorite books are:

* The Apollo Guidance Computer: Architecture and Operation - Frank O'Brien

* Digital Apollo: Human and Machine in Spaceflight - David A. Mindell

Fascinating machine.

For those interested in the engineering details behind the whole flight, from engines, to power systems, guidance, navigation and computers, I would say my favourite book is

"How Apollo Flew to the Moon" by W David Woods https://www.amazon.com/Apollo-Flew-Springer-Praxis-Books/dp/...

The Omega Tau podcast has an excellent episode featuring Mr. Woods: http://omegataupodcast.net/83-how-apollo-flew-to-the-moon/

There's also this excellent talk from CCC a few years back: https://www.youtube.com/watch?v=xx7Lfh5SKUQ

I recommend Journey to the Moon by Eldon Hall, designer of the AGC. The O'Brien book has a lot of good information but also a lot of problems. Sunburst and Luminary is also interesting, written by Don Eyles who wrote much of the lunar landing code. He goes into a detailed explanation of the 1202 program alarms.

Eyles came to the Vintage Computer Festival-East in Wall, NJ last year, and was introduced by Frank O'Brien who's a regular there. He actually did a code walkthrough of the Apollo 14 flaky-switch hack - coolest talk I've ever attended. Scott Manley did a pretty good Youtube episode on the Apollo 14 hack last year also; the two of them complement each other nicely.

Didn't know about Sunburst and Luminary. Thanks.

Excellent 1960's video demonstrating the AGC, which gives an indication of the thought processes and design rigor that were going on:


The AGC source code is up on Github these days https://github.com/chrislgarry/Apollo-11/

Ongoing effort of restoring an AGC

First episode: https://www.youtube.com/watch?v=2KSahAoOLdU

More technically accurate description: https://www.doneyles.com/LM/Tales.html

It describes that not just DELTAH was killed due to overload, but that whole system restarted (and reloaded critical landing tasks that were restart-protected)

The DSKY gets a fair amount of air time in Nova's recent episode on Apollo 8. Well worth a watch.


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