Apollo Guidance Computer Part 29: Mikes Scores a Coupling Data Unit (CDU)

Mike got a Coupling Data Unit at an auction, opens it up and gives a masterclass in Apollo hardware identification. The CDU is the box that is the root cause of the 1202 errors during the Apollo 11 landing. And his box is not what the auction advertised - it's much better!

Stuff that supports the channel:
- Amazon links for the tools I use in the lab (supports the channel if you buy from there)

Our lovely sponsors

[krisztiannemeth]

At 6:10 it was kind of hard to understand. You said "one is a sine, the other is a cosine", but on the scope there are two sinusoidal waveforms with a 180 degree phase shift. First I thought "one is a sine, the other is a minus sine". Then I realized that its not the phase of these sines, but the amplitude you are talking about. So by turning the shaft to say alpha degree the _amplitude_ of the sine waves change like sin(alpha), and cos(alpha).

[rjcroy]

Recreating the 1202 error would be such an exciting thing to see! I can't wait for that! And it would progress the explanation? Wow!

[exi]

So we got an Apollo 7 CM Upper and a Apollo 11 LM lower that has been confirmed to be put together in the lab. I cannot stop thinking that someone might just had tried to recreate the 1202 error and used exactly the perfect hardware for it that happened to lie around. Which coincidentally is exactly what you are trying to do now. Amazing thought.

[nmccw]

Oh yeah! This Frankenstein lab CDU could not be in better hands. Congrats to Mike and can’t wait to see it future videos. 👍🏻

[erickvond]

If I had to wager a guess, I'd say they built that unit up to reproduce the same 1202 error experienced in the flight module it corresponds to. Since it indicates that it was used in the lab that is. This makes it an excellent candidate to recreate the error in YOUR lab in my opinion.

[thewavesmith]

I just love watching this series, as a small child aged 6, my dad used to buy me old TVs to take apart. I was and still am at my happiest taking stuff apart to see how it works. Clearly that is often not as much fun as it used to be with things getting more complicated. But this series brings back that fun

[garbleduser]

The fact that MIKE actually got this is evidence that the universe is nostalgic for this period in history and wants to share the memory.

[benjaminhanke]

I didn't know I still have a lot of questions about the 1202 Alarm.
I'm looking forward for the next episode!

[LostAgain]

I really have to thank you for continuing the truly interesting story of the Apollo mission. I have to say we are so grateful to have Mike as a teacher and expert and he is really good at explaining what happened. Yes, all of you are really good at it. It will be really exciting to be able to follow what you find this time and how you solve it. Many thanks!

[kencarlile]

You all blow my mind. Amazing gear, amazing research, and such care. Mike sounded so very excited during the whole thing, as well he should be!

[MeriaDuck]

12:50 that bounce in Marcs voice when mentioning to open it up 🤣

[alasdairmunro]

Mike is just astounding, and a real pleasure to watch. Well done Mike & Mark!😀

[phuzz]

It's entirely possible that by now Mike knows more about the Apollo computer hardware than anyone else still alive, as he probably has a broader overview than any of the original designers.

[alexlefevre]

This series on Apollo hardware has been absolutely fascinating. I saw the Apollo 13 movie at a very young age, and this is what piqued my interest in rocketry, astronomy, and how incredible we were to have shot astronauts to our moon with this level of technology. Absolutely hooked. You guys are amazing.

[jamesberwick]

The younger generation may not know this, but back in 1969, we had no PCs, no handheld calculators, and a digital computer was wall sized for eight bits. The computer on the Appolo capsule and the one on the Lunar Lander had less memory than your cell phone. They carried as a backup, if the computer failed, the first Texas Instruments, calculator, later released in the Seventies, to the public, with a sheet on how to do all the navigation problems to return from the moon.

A month after the lunar landings, I went into the Air Force, I got trained in Navigation equipment, the computers I learned on were 40-pound boxes of gears, motors and God knows what, that calculated navigation for airplanes, along with some small amount of digital computing. My last system, on the C-5A, had true digital computers, the primary computer had 32K of memory, iron core mat memory cards, and the Aux had 16K. It took another five years before we go true PC digital computing.

[acdurn]

I enjoy all your content, but I especially love your apollo content. Today I shall dress in my Curious Marc DSKY t-shirt in celebration of Mike's find!

[bradarmstrong]

Not sure why YT brought this episode to my attention, but I'm glad it did. When I saw the title, my first reaction was "Part 29? Where have I been for the other 28 parts??" I went back and watched every one with great interest, finally arriving back here. Thanks for your team's work on the AGC and thanks for documenting this journey. This is an astounding exploration of the iconic guidance system that enabled the exploration of the moon. Your foresight to record this long road and to share it with the world is commendable. I am enjoying both the deep technical dives and your inclusion of the interviews/stories of the guidance system designers. Top drawer content for sure. Your treatment of both the hardware and the people involved will be winning the respect of audiences for generations ...

[mikemines]

Always worthwhile dropping by. Thanks from someone who was up all night to see the first moon landing.

[oscar_charlie]

Don Eyles' book, "Sunburst and Luminary", explains it well.
The AGC software was well-designed to drop tasks and restart from a known point, always making sure the high priority tasks were taken care of. That did save Apollo 11.
On the other hand, there was an issue with the stability of the descent engine, which experienced some strange throttle control issues (look up Apollo 11 "throttle castelations").
It was caused by a late chsnge in the throttle response time of the descent engine, which wasn't captured in the interface control documents and caused the software (which expected a slower-responding engine) to almost overcontrol the throttle.
That almose caused a mission abort, and it would've probably been blamed on the AGC 1201/1202 faults, at least initially.
You should invite Don Eyles in the lsb at some point, that would be a fun conversation.

Edit: for those of you who never heard of him, he was one of the main software developers on the LM AGC.

[AlexanderGibbonsAudio]

Mike is the kind of genius we all need in our lives. Thanks for keeping this series alive, it's so fascinating.