Humans first visited the Moon in 1969.  The last time we went was 1972, over 50 years ago. Back then, astronauts in the Apollo program made their journeys in spacecraft that relied on remarkably basic electronics that are totally unsophisticated compared to what you might find in an expensive blender or fridge these days. Core among them was the Apollo Guidance Computer, charged with keeping the craft on target as it travelled to its destination and back again.

Marc Verdiell, also known as CuriousMarc, is a bit of a dab hand at restoring old vintage electronics. Thus, when it came time to restore one of these rare and storied guidance computers, he was ready and willing to take on the task. Even better, he came to the 2023 Hackaday Supercon to tell us how it all went down!

Restoration

You might have heard whispers of this effort before, or seen some of our prior coverage. Indeed, the effort to resurrect this Apollo Guidance Computer (AGC) began in earnest back in late 2018. This particular example of the AGC was found in an electronics recycler in 1976, and the plan was to restore it prior to the 50th anniversary of the first Moon landing in 1969. Marc worked with Carl Claunch, Ken Shirriff, and Mike Stewart on the project, and documented much of it on his YouTube channel under the name [CuriousMarc].

As Marc explains, Apollo actually had four main computers. There was the Launch Vehicle Digital Computer (LVDC) which was charged with steering the Saturn V from launch, along with the Flight Control Computer which was actually an analog machine. There were then two identical Apollo Guidance Computers (AGC)—one was in the Apollo Command Module (Apollo CM), and one was in the Lunar Excursion Module (LEM). There was also the Abort Guidance System for handling any situation where things got out of hand. With the aid of old NASA diagrams, Marc shows us where the AGC lived in the Command Module and the LEM.

The Apollo program marked the first time humans had trusted the piloting a spacecraft or aircraft to a computer system. The AGC was designed by MIT, built by Raytheon, and it weighed 70 pounds and drew 50 watts. While it looks bulky and heavy by today’s standards, it was wildly compact and efficient by 1960s standards. The interface for the AGC was the DSKY—short for “Display and Keyboard.” It’s how the astronauts controlled and interacted with the AGC during the mission. The AGC was absolutely mission critical. In the words of NASA engineer Dan Lickly, ‘The AGC did everything.” It was responsible for orienting the spacecraft, controlling rocket burns and guiding the craft into orbit, and for handling the landing of the lunar module as well as re-entry into the Earth’s atmosphere.

Marc tells us how one example of the Apollo Guidance System ended up at an electronics scrapper in 1975, by order of one of NASA’s engineers. It soon ended up in the hands of hacker Jimmie Loocke, who got his hands on a full two tons of Apollo program hardware. Years later, one Mike Stewart reached out to Jimmie, hoping to look at a real AGC and take some measurements for the sake of working on a replica. When this was happening, Jimmie in turn asked if the device could be powered on, and eventually a team was assembled to try and make that happen. The first attempt happened in a Houston hotel room in October 2018, and the project took off from there.

The talk includes tons of glorious internal shots of the AGC, serial number RAY 14, which was built for an engineering test series. The AGC was assembled from stacks of neatly-arranged modules full of integrated circuits, all connected through an elegantly wire-wrapped backplane. In fact, this was one of the earliest computers that relied on integrated circuits. All of these were dual 3-input NOR gates or analog amplifier ICs. As non-flight hardware, most of the modules in this AGC weren’t potted, which had the benefit of making them easier to work on. However, two of the modules for the core memory did have potting which would make them harder to work on.

Repairing and restoring the AGC was aided by official schematics, so the team knew what they were working with. Modules were tested, and the core memory—essentially the RAM—was found bad. There was also no core rope memory—essentially the ROM for the AGC which stored the program. A rope memory emulator from Raytheon was used instead for this engineering test article. This was for ease of development, as it allowed changing the stored program more easily than rewiring a core rope memory device. However, the Raytheon emulator device was undocumented, which took some reverse engineering work to figure out. Still, powering up the device with no RAM or ROM was a positive experience—the AGC still tried to boot and there were some minor signs of life.

The rest of the talk outlines how the AGC was brought fully back to life. The team improvised an FPGA memory emulator, X-rayed failed components, and built replicas of things they couldn’t replace, all in service of the final goal. Sneaky hacks were used to get bits and pieces functional again against the ods.Even connectors had to be remade from scratch since the AGC used long-forgotten standards that are no longer in use. The fact that Marc works for connector supplier Samtec proved particularly useful in this case. Prepare to choke on your beverage when he explains how much that cost.

We won’t spoil the whole journey here, because Marc’s talk is worth watching from start to finish. There are plenty of twists and turns, and all along, you’re waiting for that ultimate delight—the joy every hacker knows when the beleagured machine finally roars into life. Never mind the wonderful heartwarming moments at the end.

It’s simply wonderful to see a dedicate team bring this storied hardware back to life—and even better to see them flying simulator missions with the real AGC hardware doing its thing. It’s a fantastic restoration effort and one that was documented in intimate detail, and it’s joyous that we get to see everything that went into making this happen.