Decoding Rediscovered Rope Memory From the Apollo Guidance Computer

On August 25th, 1966, an Apollo Command Module was launched aboard a Saturn IB rocket in mission AS-202. This mission was intended to immediately precede the ill-fated Apollo 1 mission, the AS-202 was unmanned, serving as a test of flight hardware, fuel cells, and the guidance and navigation control systems. This mission used the first Apollo Guidance Computer ever flown, and this mission was vital to testing the computer that would take men to the moon.

While the software from the later missions exists and is available on Github, the earlier Block I spacecraft, including the unmanned Apollo 4 and Apollo 6 missions, are poorly documented. [Francois Rautenbach] was lucky enough to get his hands on the rope memory modules from the AS-202 mission. Now he’s investigating these modules with oscilloscopes and x-rays to recreate some of the first software that was flown in space.

The procedure to extract the data from these rope memory modules is a bit harder than reading a bit of Flash off a chip. Rope memory is weird, but with a contraption made out of a lot of relays and an oscilloscope, [Francois] was able to capture data from these memory modules.

Of course, [Francois] first needed to figure out the pinout for the gigantic backplane connector on each of these memory modules. To do that, he checked out a Block II AGC, read the schematics very carefully, and reverse engineered a connector that isn’t made anymore. The next step was x-raying the rope memory modules to see how they were assembled. Even though these memory modules contain the only extant copy of the Block I AGC software, even reading one bit off of these modules is an amazing case of technological archeology.

The answer to the obvious question — where did these modules come from — is exactly what you would expect. These memory modules were picked up off a scrap heap forty years ago. The gentleman who found these modules was kind enough to give them to [Francois]. Check out the videos below for [Francois]’ video logs. If you’re into slightly more destructive testing of forgotten Apollo flight hardware, [Fran Blanche] tore down a few modules from the Apollo Launch Vehicle Digital Computer a few years ago.

Thanks to [Vincent], [Danie], and [Kent] for jumping on this one and sending it into the tip line.
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[Fran]’s New Project: The DSKY

[Fran] has already made a name for herself in some retro cool historical aviation and computer circles by tearing down a flight-ready spare of a Saturn V launch vehicle digital computer, the computer that was responsible for getting all flights to the moon into low earth orbit. Now she’s ready for another project, and again, this is something that hasn’t been done in 40 years. She’s building a DSKY, the control panel for the Apollo Guidance Computer

The Apollo Guidance Computer is a well-documented piece of computing history, with homebrew versions all over the web. The DSKY is only one small part of the AGC, but it is by far the most famous module. Being the only user interface for the AGC, it’s the only part of the AGC that gets all the screen time in Apollo 13, the travesty on BluRay that was Apollo 18, and is the only device that bears any physical resemblance to its real-life counterpart in a number of AGC simulators.

That’s not to say DSKY builds haven’t been attempted before; there are a few out there using LEDs and off-the-shelf buttons for the build, but the DSKY from the mid-60s is much, much cooler than a bunch of LEDs and light pipes. The eery green numbers are actually EL displays. Guess how those displays are controlled? Relays. It’s a masterpiece of technology, made even more impressive in that the folks at MIT who built the thing didn’t have anything better to build the display with.

Because of her deconstruction efforts with the Saturn V LVDC, [Fran] was invited down to the National Air and Space museum in the middle of Washington DC. There, she saw everyones favorite ugliest spacecraft, the Apollo LEM, along with an incredible assortment of paraphernalia from aviation history. The Wright Flyer – yes, the original one – is hanging from the ceiling next to the Spirit of St. Louis, and X-15 rocket plane, right above the command module Columbia from Apollo 11. Copies of probes currently rolling over Mars are on display, and you can walk through a training model of Skylab. If you’ve never been, spend half a day there, then take the metro out to the Udvar-Hazy center, where you’ll find all the stuff they couldn’t fit in the downtown collection like a Space Shuttle and a Concorde.

This is only the first part of [Fran]’s vlog documenting the construction of a copy of the DSKY, and we haven’t even seen the inner guts of the most famous part of the AGC yet. She’s been working on this for a while now, and there’s no doubt she’ll finish the job and come up with the best replica of a DSKY ever.

Hackaday Links: December 22, 2013


[Korben] is using a picture frame as a Bluetooth speaker (translated). He hacked a Rock’R² for this project. It’s a device that has a vibrating element which can be used to make any hollow item into a speaker.

Entertain yourself over the holidays by mastering the Apollo Guidance Computer simulator. It’s a JavaScript version of the computer used in the modules of the Apollo moon missions.  [Thanks Gregory and Paul]

Here’s a little mirror attachment that lets you use your laptop as an overhead projector. [Ian] calls it the ClipDraw. Affix it to the webcam and use the keyboard as the drawing surface. Since it’s simply using the camera this works for both live presentations and video conferencing. What we can’t figure out is why the image doesn’t end up backward?

This guide will let you turn a Carambola board into an AirPlay speaker.

Those who suck at remembering the rules for a game of pool will enjoy this offering. It’s some add-on hardware that uses a color sensor to detect when a ball is pocketed. The Raspberry Pi based system automatically scores each game.

We spend waaaay too much time sitting at the computer. If we had a treadmill perhaps we’d try building [Kirk’s] treadmill desk attachment. It’s made out of PVC and uses some altered reduction fittings to make the height adjustable. It looks like you lose a little bit of space at the front of the belt, but if you’re just using it at a walking pace that shouldn’t matter too much.

You can have your own pair of smart tweezers for just a few clams. [Tyler] added copper tape to some anti-static tweezers. The copper pads have wires soldered to them which terminate on the other end with some alligator clips. Clip them to your multimeter and you’ve got your own e-tweezers.

Apollo Guidance Computer clone

[Cliff Miller] pointed out this incredible project from 2004. [John Pultorak]’s journey began in late 2000 when he decided to build a 60’s or 70’s era minicomputer. While gathering technical documentation, he found some interesting information on the Apollo Guidance Computer and felt that was the way to go. The AGC was the first integrated circuit computer ever built. Designed by MIT in 1964 it was constructed from ~5000 ICs, almost all 3-input NOR gates. [John]’s version uses late 1960’s 74LS TTL logic which gains him a 10 to 1 reduction in the number of ICs. A good thing when you have to do ~15K wirewrap connections. He also used flipflops and register chips instead of building everything from NOR gates. [John] essentially built the AGC three times: First, he coded a simulator in C++. Then, he imported the logic design into CircuitMaker to verify that it would actually work. Finally, he built the 3 by 5foot machine. He’s provided an amazing amount of documentation for anyone that wants to explore this device and the overview alone is well worth a look.