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with the IMU ball, cooling system and all of the interconnect, an artifact in the Future Ventures’ 🚀 Space Collection.
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UPDATE: the CollectSpace community is just incredible. Overnight, they identified the Apollo Guidance Computer. Amazingly, it comes from the second Lunar Module, LM-2…. the one that is in the Smithsonian! Documentation of its history starts in 1967. The rope-core memory modules contain the Aurora program for the Apollo 14 Lunar Module where they were used for extensive testing before launch. It was listed as a flight-worthy spare for Skylab, and finally, it was used extensively at Edwards AFB with new interface modules to test the first use of digital fly-by-wire (DFBW) technology in F-8 jets in 1972, and finally implemented in the space shuttle.

UPDATE 2: The accelerometers in the IMU Ball flew to the moon and back on Apollo 12, and other parts flew on Apollo 7 and 9.
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I am still doing research on this one, and it is fascinating. The Apollo Guidance Computer (AGC) is a module at the bottom of the stack on the left, revealed in comment stream below. And at minute 2 of this impromptu video, you can see the whole rig.

The program it contains is “Aurora revision 88”, the final release of the Lunar Module system test program. Current belief is that this rig was used subsequently for research into F-8 Digital Fly-By-Wire control used on the Shuttle eventually (NASA summary). Thanks MStewart and Spaceaholic for help on this.

RR Auction is about to auction the first AGC ever seen for sale: “The Apollo Guidance Computer was a technical marvel: in the era of room-sized computers, NASA allocated one cubic foot on their spacecraft for the electric brain that would be responsible for guiding humans to the lunar surface and safely returning them home. It was up to the best and brightest at the MIT Instrumentation Lab to make it fit. Rather than using the large vacuum tubes or big discrete transistors typical in computers of the time, MIT engineers pioneered the application of integrated circuits—microchips—to accomplish the same task in a diminutive package. During 1963, the Instrumentation Lab consumed 60 percent of the integrated circuit production in the United States, and by 1964 Fairchild Industries had shipped more than 100,000 ICs for use in the Apollo program.

The AGC hardware was thus a combination of cutting-edge technology and old-school craftsmanship: while these innovative, mass-produced chips made their way into the AGC’s logic modules, the computer’s mission-critical software was stored in handmade ‘rope memory,’ contained inside its fixed memory modules, which could not be erased, altered, or corrupted. This rope memory required absolute precision and was sewn by workers recruited from local textile factories: copper wire was woven in and around ring-shaped magnetic cores, with each wire threaded through the core representing a binary “1,” and each wire bypassing the core representing a “0.” It took eight weeks for the workers to weave the memory for a single flight computer, at a cost of $15,000 per module.

Developed using a mix of assembly language and an interpreted mathematical language, the software contained on these modules was as innovative, and as important to mission success, as the pioneering hardware. Many of the design principles developed at MIT for coding the AGC became foundational to software engineering in general—particularly in the design of critical systems that rely on asynchronous software, priority scheduling, fault-tolerance, fly-by-wire capability, and human-in-the-loop decision making.” (update: it just sold for $280K)

Back to my AGC, it is P/N 203993-091, S/N Ray 26.

The memory modules are:
Memory B1 2003972 -011 Ray 86
Memory B2 2003972 -091 Ray 87
Memory B3 2003972 -111 Ray 115
And the memory jumper modules are 2003076 with -021 and -031, and S/N Ray 1, 2 and 5.

10 responses to “Apollo Guidance Computer (AGC) and Navigation System from the second Lunar Module, LM-2”

  1. Inertial Measurement Unit, P/N 2018806 Rev E, Cured 1-67 Mutron Corp.With Interface Box Assembly pulled aside, the AGC is visible bottom leftZooming inOne memory module pulled outconnector on other side Other side, with AGC at the bottom. The various pipes run to cooling plates under each block of electronics:Tag on top: Apollo G&N System Power & Servo Assembly – LM P/N 6007200 S/N AC 14 Cont. No. NAS 9-497
    The GM/Delco tagged boxes are for the Digital Fright Control System interface, where this AGC lived a second life. It was repurposed to do the first test flight of Digital Fly-By-Wire aircraft, paving the way for all military and commercial jets today. You can see my AGC at the top of the DFBW F-8 test vehicle.

    Down at the bottom, connected to the AGC: "DFCS Interconnect Harness A" with "STAGE III SIM & FLT" and S/N 2 Part No. "MX117926 NASA/FRC DFCS"and the tag from box on other side, "Interface Box Assembly" each with "STAGE III SIM & FLT" S/N 1 Part No. "MX117925 NASA/FRC DFCS"LM-2 images from the Smithsonian, a chapter in Milestones of Spacewith the Apollo 11 astronauts.

    and some detail on the hand-weaving of the rope memories:

  2. Technology in leaps since that time.

  3. Stanley Kubrick must have seen these fixed memory modules and the way they mount by two hex screws and slide in/out of trays > HALs brain’s are so similar…albeit much cooler looking with all that red glow 😉

  4. Core rope ROMs > "data density of 72 kilobytes per cubic foot, or roughly 2.5 megabytes per cubic meter." But very stable…you have to damage the wire or wrapped cores or the connection substrate to make them unreadable. >> "the Block II Apollo Guidance Computer used 36,864 sixteen-bit words of core rope memory (placed within one cubic foot) and 4,096 words of magnetic core memory (within two cubic feet)."

  5. So, the Apollo Guidance Computer ran on 36KB + 4KB = 40KB of ~machine code >> about the same data we fling around today for very (very) simple web pages.

  6. amazing…so, less than my 48K Apple ][

    The IMU ball is itself a work of art, an incredible electromechanical gyro inside a gyro. Here is a writeup I did on another one I have, to peer inside:

  7. Friendly suggestion: try to keep Caplugs over the connectors and coolant hose ends. This is a very rare artifact.

  8. Just today, I found my LM-2 AGC in a book Computers Take Flight about the development of digital-fly-by-wire. My unit was in that plane (in this NASA photo, up top in the avionics bay, and note the DSKY at the bottom). It had custom interface circuitry boxes added and we have all the wiring harnesses intact… so, even if potted, I would think the test interface woudl be useful… it could fly a lunar module and an F-8 after all!

  9. More on the Inertial Measurement Unit Ball: new archival document research sheds light on the components inside the IMU ball, repurposed from various Apollo flights. Specifically, all three PIPAs inside it were the same ones that flew Apollo 12 to the moon and back!

    For the IRIGs, this IMU has:
    7A-27 — Just flew on the F-8 DFBW
    7A-69 — flew on Apollo 9 as part of IMU 14
    7A-85 — flew on Apollo 7 as part of IMU 8

    The IMU was gimbaled on three axes. The innermost part, the stable member (SM), was a 6-inch beryllium cube, with three gyroscopes (IRIG) and three accelerometers (PIPA) mounted in it. Feedback loops used signals from the gyroscopes by way of the resolvers to control motors at each axis. This servo system kept the stable member fixed with respect to inertial space. Signals from the accelerometers were then integrated to keep track of the spacecraft’s velocity and position.

  10. And now, a Curious Marc video of Mike’s readout of the Aurora 88 program from the core memory bank: http://www.youtube.com/watch?v=k2Ji-55FOGQ

    Aurora 88 is the first LM rope ever produced, representing the complete LM AGC test set. Mike is doing more Apollo SW recovery than all the museums in the world combined.

    And here is my earlier post on the DFBW programHow the Lunar Module improved flight on Earth  ✈️

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