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!
Apollo Guidance Computer Playlist: • Apollo Guidance Comput...
Stuff that supports the channel:
- Amazon links for the tools I use in the lab (supports the channel if you buy from there)
www.curiousmarc.com/amazon-links
- Channel merch on Teespring: teespring.com/stores/curiousm...
- Support us on Patreon: / curiousmarc
Our lovely sponsors
- PCBWay: fast turn PCBs, www.pcbway.com
- Electro-Rent: www.electrorent.com
- Keysight: test instruments: www.keysight.com
- Samtec: connectors: www.samtec.com
- R&D Microwaves: rdmicrowaves.com
Get more technical info on the companion site: www.curiousmarc.com
Contact info: kzbin.infoa...

[@krisztiannemeth6148]

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).

[@CuriousMarc]

You got it exactly right. It’s the amplitude of the waveforms that’s proportional to the sine and the cosine of the angle. Which brings about one major complication: it’s not enough to measure the amplitude of the resulting signal, you also have to measure the sign. Which you also got right, the sign is in the phase of the signal, either in or 180 deg out of phase with the excitation. It’s the phase part that got messed up and eventually caused the 1202’s, in a very complicated and round-about way. We’ll explain this in more details in future videos.

[@Kae6502]

@@CuriousMarc Thank you Marc, This is going to be epic! This piece of history couldn't have ended up in better hands!

[@wdavem]

Thank you! I actually understand this now correctly for the first time, and I'm 43!

[@benswinter]

@@CuriousMarc I absolutely cannot wait for this update where you explain this theory and test it. As an EE you guys and your command of knowledge and theory are a marvel to watch. Thank you thank you for these videos, please don't stop :)

[@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!

[@thewavesmith5754]

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

[@-allround-]

Same here, on my birthday mostly got old video players en old radio's

[@BGTech1]

Same here. About 14 years ago (I’m 17) I started taking apart my little brothers toys. He wasn’t too pleased so my parents got me other electronics to take apart. I’m pretty sure this is how every future engineer begins their Journey

[@Pickelhaube808]

A very trusting parent to let a 6 year old dig around inside 30kV electronics!

[@-allround-]

@Pickelhaube In those days parenting workt different , not a bubble wrap society like nowadays

[@simonhanlon7518]

Ha same here, I remember my Dad showing me, at the age of 7, how to discharge a CRT.....and how to repair a LOPT with araldite.

[@jamesberwick2210]

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.

[@nmccw3245]

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

[@MeriaDuck]

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

[@CuriousMarc]

Mike, please, pleeeeeeease!

[@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.

[@fredericlepeltier3435]

My tought exactly!

[@erickvond6825]

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.

[@grahamheath9957]

That was exactly my thought also. That type of playing freely with the specs of parts as compared with the official build is exactly like what happens in labs when you have a specific task and only care about replicating certain functions

[@benjaminhanke79]

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

[@lostagain2706]

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!

[@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.

[@MDBenson]

Amazing work from Mike, that guy's probably one of the most qualified spacecraft historians on earth by now, I am pretty sure he's forgotten more about the Apollo program than I've ever known (and i his case probably still has the document with it in anyway, and knows how to find it again!). Every single morsel you uncover in this series is fascinating, thank you for brining it to us in such a great series of videos.

[@phuzz00]

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.

[@ac1d8urn]

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!

[@tomteiter7192]

Does Mike have photographic memory? I watched the whole Apollo series, and the amount of detail in Mike's brain is simply stunning. I'd wager there never existed another single person with such a complete understanding and overview of the whole Apollo computer systems. It's an utter delight to watch and listen to you guys (including Ken Shirriff...)

[@molletts]

He has holographic memory - connected directly to his positronic brain ;) Seriously, though, I'm in awe of his knowledge and skills. He's not just in a different league to most of the rest of us, he's playing a totally different game.

[@tomteiter7192]

@@molletts indeed. The FPGA based AGC Test equipment emulator with accompanying software for example is such a genius combination of skills, it boggles the mind. Even while I understand the parts involved, the whole thing together is just stunning

[@alasdairmunro1953]

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

[@kencarlile1212]

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!

[@2stroke4me]

The amount of R&D that went into the Apollo program boggles the mind. Equally mind boggling is the amount of research and knowledge you guys have about the history of the Apollo program. Mike seems to be an indispensable member of your team! Although i'm very unfamiliar with computer hardware and software, i'm fascinated by it all and in the meantime i learn a thing or two. It's like archeology! Great stuff guys!!

[@zoomtruth1013]

Weird how nasa still won't test a human in their space suit while in a vacuum chamber!!

[@rearspeaker6364]

@@zoomtruth1013 must be the Closter phobia!!

[@alexandrebustico9691]

AGC series update, that's nice ! And since that episode was recorded 8 months ago, I suppose that a lot of discoveries has been made since, one can hope that a new AGC season is on his way :-)

[@alexlefevre3555]

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.

[@smacedorj]

The happiness in Mike's face... 😁

[@MrHichammohsen1]

This series just keep getting better and better!

[@mikemines2931]

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

[@DavidThomasScorbal]

There is one person who is likely even more interested in your 1202 findings than the rest of us, and his name starts with Buzz Aldrin. If you find something significant, I hope your circle includes some way of contacting him with the info!

[@bru57000]

I thought 1202 alarm was because Buzz took the liberty to turn on the radar, taking too much CPU cycles, and not in accordance with the procedure.

[@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.

[@DavePKW]

I am so glad the Apollo journey continues. I love the research you guys are doing. Thank you.

[@lineshaftrestorations7903]

In my software coding carreer I used many AtoD an DtoA devices as well as resolver to digital convertes. Most were 40 pin integrated circuits weighing mere grams. Amazing the technology leap from the massive Apollo module to the diminutive devices I worked with. The documentation of revisions and errata are still practiced today to the mental stress of engineers.

[@AlexanderGibbonsAudio]

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

[@makusmati]

That was an amazing series to follow. What a great team and really perfect combo of brainiacs to lovingly restore this piece of space exploration history. Well done!

[@steve_case]

Great work. Congrats to Mike for the acquisition. Holding my breath for the final proof and announcement of your theory. Will give more light to the phrase “We’re go on that Flight!”

[@TheKrokogil]

Thanks Marc and Mike, really exciting, waiting for further developments

[@marianaldenhoevel7240]

Aerospace hardware plus pedantic history is just sooo sweet to watch. Dr.Jones Jr would try to tell us "it belongs in a museum". But I have to disagree. Putting it into your gangs hands is a much better home for it. Congratulations to you and thank you very much for sharing with us!

[@Luzgar]

It's really amazing that this channel took off and is always producing some excellent content on impossibly rare and specialized hardware.

[@youtubeuser6067]

Luck favors the prepared mind. Excellent episode.

[@tristshapez]

Love this quote ♥️

[@WellingtonIronman]

Honestly can’t get enough of the Apollo hardware series. Having the two of you analyse and dissect every component while linking it back to the actual functions of the spacecraft is fascinating. You and Mike are a force of nature. Thank you for all your work!

[@chadhauze1683]

This series, and all your videos are fantastic! I love all the archaeology that goes into determining just what the equipment is.

[@justforfunvideohobby]

Mike deserves this priceless relic. He's so cool & smart! Nice job scoring that one dude.

[@mlehky]

Still eagerly awaiting the next episode….you really left us hanging in this one.

[@timothyp8947]

The fantastic range of exceptional expertise in such a wide range of topics that gravitate to become part of the CuriousMarc team never ceases to amaze me! Fascinating piece of kit, fascinating research and detective work by Mike to determine how it came to be. Another cracking episode - thanks team!

[@bradarmstrong3952]

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 ...

[@prjndigo]

So what I'm getting is someone assembled a unit to test the 1202 error theory out but it didn't get documented.... so you not only found a unicorn, you found the _exact_ unicorn you needed.

[@jonathanhendry9759]

I wonder if that combo was put together originally by someone to reproduce the 1202 error.

[@KallePihlajasaari]

That would be an amazing coincidence. Perhaps they find another memo one day that hints at this. Not sure of the timeline, this may have been Frankensteined before the error occurred.

[@kenchorney2724]

The excellent book "Digital Apollo" by David A. Mindell has a section explaining the origin of the 1201 and 1202 alarms during the Apollo 11 descent on pages 227 through 233. This book is a very good read.

[@mikestewart8928]

It is indeed a good book, but Mindell unfortunately reproduces a lot of popular misconceptions in that section talking about the program alarms. Don Eyles's book Sunburst and Luminary digs into more (and more accurate) detail from the software side, but to my knowledge there aren't any books that get it fully correct from a hardware side.

[@kenchorney2724]

@@mikestewart8928 I will have to get Don Eyles's book.

[@Obladgolated]

Congratulations on a remarkable job of restoration, both of hardware and documentation system!

[@neillthornton1149]

One thing resolvers are being used for is SATCOM antennas on board ships at sea. Much like the rendezvous RADAR, dishes need to be locked on to their corresponding satellite even as a ship is bobbing and weaving on the waves. It's mesmerizing to watch them stay perfectly still in relation to the bird, but have the pedestals moving around with the ship.

[@Moonlight0551]

Well done guys. I love the care with which Mike takes apart the precious hardware. A half turn of each screw on different corners. Don't see that these days in the local workshop.

[@EcBaPr]

great to see you have more episodes in this series..

[@joswhite7923]

Bravo. Keep up the excellent work. It is grand fun to see the back story of the moon missions.

[@srOmatic]

So many thanks for this part 29 ! This channel is gold. Curious Marc, Master Ken and the modest and brilliant Marc form a unique trio. Live long and prosper \\/ ;)

[@davidwellings2783]

Absolutely fascinating stuff - LOVE it! Brilliant work guys!

[@ifitsrusteditsmine]

This has to be the BEST KZbin channel (elevator music included)

[@danielhoven570]

I work on optical sensors for modern spacecraft IRUs, cool to see the similarities and differences between then and now.

[@talesmaschio]

Another great episode on this series! Looking forward for the next one!

[@privatepilot4064]

Of great historical significance. I fondly remember the entirety of the Apollo program from a pubic perspective. And as a kid, I was fascinated by it. These components are such an important part of our national history. Great video.

[@gurueddy]

I am constantly stunned by the achievements of the engineers who put the Apollo systems together. Ingenious design using the technology of the time, operating in the harshest environments, severe weight limits and achieved under a decade. 😮👏👏👏👏👏👏

[@nuffsaid0]

Honestly, what a thrilling story, I love it!

[@StevenScalia]

Thank you for the elevator music explanations. You do a great job explaining how these parts work.

[@frequentflyer56]

Brilliant detective work Mike. Many kudos

[@LMacNeill]

Wow -- *really* looking forward to finding out your theories about the 1202 error, and Mike's experiment to prove his hypothesis. I will definitely tune in for those videos when you release them!

[@Embarking-on-a-new-adventure]

Again a fantastic video, can't wait for more. Succes from The Netherlands

[@Sailor999999999999]

I am so envious of your new collection.

[@davidblauyoutube]

Amazing documentary! Keep up the great work!

[@spikeypineapple552]

So cool to see Mike so excited.

[@hoofie2002]

Looking forward to this series going to be fascinating!

[@peterhudson4027]

Having watched the resurrection of the AGC I feel like you two are almost family by now! Can't wait to see how this next project unfolds

[@davidkilpatrick1640]

Woohoo .. a new CuriousMarc video!

[@paulstubbs7678]

It never ceases to amaze me the weight of all this hardware, no wonder the F1 engines were so powerful.

[@KallePihlajasaari]

Space-X has it easy with a few flat panel displays controlling the whole rocket with CAN-BUS or similar. The moon landing was an achievement that took the resources of a industrialised nation to pull off. The same could almost be done now by Elon if someone were to pay for the fuel.

[@paulstubbs7678]

@@KallePihlajasaari I'm not really talking about the tech, but the crazy heavy boxed etc they built them into. He's luck he didn't pull a hernia getting that CDU out of the transport box.

[@MarcelHuguenin]

Congrats Mike with this new treasure! I am always amazed by the shear amount of knowledge you guys have on the Apollo hardware and technology. It's a joy to watch every time. Curious to see what this will bring!

[@moki123g]

What a great score! It is amazing to me that all of that beautiful hardware could be replaced with a $2 micro controller and a little glue logic today. We've come a long way...

[@JensAndree]

It wouldn't be radiation hardened nor robust enough to trust it for a space mission though... Just saying. There's a reason why NASA is still using those obsolete Motorola CPU's for their space hardware since they're proven and verified. They need to find a replacement soon. Perhaps the MC68000, or a 286 can do the job?! ;)

[@ptonpc]

Great detective work!

[@ricardobornman1698]

What an awesome piece of history.

[@vibrolax]

Now let's find Eagle's ascent module in lunar orbit, and recover it.

[@KallePihlajasaari]

And pair it with a lander. Patch together a command module and all that is needed is a service module.

[@djmips]

Fascinating as usual!

[@guyh3403]

This is soooo amazingly interesting. Thank you very much!

[@wizard-pirate]

Mike has untold magical powers beyond any other.

[@Chriss120]

it is stunning to me how much written data is collected about a piece of hardware produced so many years ago.

[@mnoxman]

Your description of the resolver reminds me of a sensor that's used in other places called a linear variable differential Transformer (LVDT). I have seen them used in a couple of different applications back in the early 90s when I used to do such work.

[@Jack_Luck.v2]

Remember kids, we didn't go to the moom, we just made all the computers and technology to go, but faked the rest.... sarcasm. This stuff is pretty sweet, keep up the good work CuriousMarc. It has always been a great time watching your videos.

[@kingofcotham9999]

Absolutely amazing!

[@FrozenHaxor]

Nice score Mike! Definitely a keeper!

[@MikeWest_W]

CuriousMarc and MethodicalMike congrats!!

[@christianvanderstap6257]

Thank you, my inner nerd enjoyed this a lot

[@bensmith3304]

Man, what a lucky find! Cashing in some major karma points there.

[@syntaxerorr]

I love watch these videos about the old Apollo computer systems. Thanks! I recently heard about the star navigation system on the SR71 and I'm supper curious as how a system like this might work? I would think it would be similar to the Apollo star navigation, but I have no idea! Please do a video on it!

[@skfalpink123]

It's funny to think that had NASA hung on to all of that hardware, it would probably (for the most part) just be gathering dust on shelves. Outside of NASA it has taken on a whole life of its own, educating tens of thousands of historians, hobbyists, scientists and engineers. Fascinating stuff.

[@stevekoehn1675]

This looks like so much fun, I'm jealous, and I'm never jealous!

[@-r-495]

From a lab to a lab. Perfect!

[@larsbr4519]

Awesome, Thanks for sharing.

[@markfacca]

Very cool - Mike should right a technical book on all things Apollo.

[@chewierama49]

Happy to see the project continue ! is there a chance to know what happened to the AGC you revived ? not in plain details but in general ? is it returning to the channel or is it stuck in a collection somewhere ?

[@CuriousMarc]

Sadly it’s gone. We have no clue where it went.

[@aserta]

Great score!

[@tekvax01]

Where do I find an auction like this?? Excellent job Mike and Marc!

[@stevec00ps]

This is just awesome :)

[@brandona1370]

I am so excited for this!!!!

[@billmeyers3058]

My old mentor would reminisce about his days in technical college. His professor had a nasty habit of "pranking" there breadboards. He would pull a random wire, remove the copper from the insulation sheathing with tweezers, cut the copper, then sheath it back in and replace it!

[@occamraiser]

I like to think that I'm technically pretty well educated and experienced after a lifetime of working in Electronics and Software development since the 1980s. But I am always just stunned by the depth AND breadth of knowledge of real electronics and technology enthusiasts.

[@Graham-ce2yk]

Fascinating stuff, I've heard that Mike has built a device to help recover more Apollo software from core ropes, hopefully it will put an appearance in on the channel soon. Also a question regarding 'Retread 50' (Episode 15), has any further testing been done on it since it's recovery and if so, what has been discovered?

[@douro20]

Resolvers are quite often found in the output shaft on hybrid car transmissions as a source of angle data for torque vector control. Vector motor drives are often used because they provide very good control of output torque at varying RPMs.

[@buzz1ebee]

Amazing find! Did they let you inspect the unit at the auction house? Did you have an inkling about what it might actually be? I'm also curious about who the other people buying this stuff at auctions are. What are they doing with the equipment after they buy it?

[@Petertronic]

I'm curious about who was selling all this stuff! Of course, auctions always keep that private.

[@mikestewart8928]

I didn't get a chance to inspect it beforehand, but I did have an inkling there was something weird about it. The listing stated that it weighed "roughly 39 pounds", while the maximum allowable weight for a CM CDU per the engineering drawings is around 37 pounds. I couldn't think of anything that would explain that weight difference other than a measurement error or possibly there being modules in the slots that should be unpopulated -- but given that the thing was still pressurized I thought the latter was pretty unlikely.

[@Fs3i]

By the way, I hope y'all got at least a cut of the $740k, as you really helped increase the value of the AGC.