How Engineers Designed The First Computer To Fly In Space

[@bobbycfpv8578]

Hi Scott! I am lucky enough to be friends with Tom Stafford who flew two Gemini missions. Tom solved the differential equations for the orbital mechanics of their mission ahead of time. He could calculate the maneuvers parameters using a slide rule and beat the computer in coming up with answers.

[@ropersonline]

Did they still make him use the computer anyway to double-check? Trust but verify?

[@b.thomas8926]

I'm not surprised, honestly. We really did send our best up there.

[@shaeby8123]

@@ropersonline Back then, It would likely be the other way around. Computers were still unreliable at best, and so, for a long time, after the computer were done doing calculations, someone would follow-up to make sure that it was reading right.

[@ericchin739]

Back then, it was more common for a person to do the calculations and use a digital computer for verification. Digital computers were very slow back then

[@rayoflight62]

I would like to add - those glass delay lines reached worldwide fame few years later, when color TVs all over Europe required the simultaneous process of two horizontal scan lines (to average the colour phase) - and this was achieved with a glass delay line of 64 μS, a direct descendent of the NASA one you mention in the video. Thank you Mr. Manley for all your efforts and dedication. Greetings from the UK, Anthony

[@BurnleyNuts]

I remember the little blue Philips delay lines developed in Eindhoven, these were made of quartz, same thing though and delayed the faster luma signal while the slower choma signal caught up. It's amazing how you easily forget these little pieces of technology these day. Brings back a lot of memories of items such as burst detection, colour killer and the varicap diode. Also the way Green was very cleverly re-constituted from 100% - (B-Y) - (R-Y) to save bandwidth in transmission. some really clever guys back then working on TV technology which these days is so taken for granted.

[@Rob2]

@@BurnleyNuts Another noteworthy fact is that in those days every development in consumer electronics was done in a backward-compatible way. Color TV signals could be viewed on a B&W TV. Stereo radio transmissions could be received on a mono receiver. Etc. Today, whenever a new transmission mode or feature is devised, all existing equipment gets an immediate trip to the electronics recycling (or the landfill), and everyhing has to be bought new.

[@ImieNazwiskoOK]

@@Rob2 Similarly with ability to be repaired and such

[@zlm001]

​@@Rob2 Dude, we're doing way more clever things with technology today than adding color to a black and white signal and having it work on old and new systems.

[@BurnleyNuts]

@Queewe Kind of true although valves or tubes as Americans like to call them aren't/weren't specific to TV's. Glass vacuum valves were around in the early 1900's and in effect work as electronic switches and amplifiers so eventually found their uses in early radio and transmission technology and of course during the war effort used to great effect to create physically huge computers such as the Enigma code cracking Colossus. As the valves are capable of switching two states, the early principles of binary code could be utilised albeit in a very cumbersome way. Once transistors came along in the 1950's that massively miniaturised everything. Isn't the progression of technology amazing!

[@the_Texas_Bandit]

Absolutely no wonder why you have a million and a half subs. Best presentation on something I have craved since I was a child. I learned Mercury as a child. Built a mockup with my Grandfather. 1/3 scale. We had compressed air thrusters, and bubble levels to yaw pitch and roll. Summer of 66 was the best of my life. Thanks Pop !

[@ninehundreddollarluxuryyac5958]

Gemini was the coolest spaceship. Basically a two seater sports car. It had everything you needed to navigate and maneuver in orbit, even find and intercept another spacecraft and dock with it. But it had all of this in something the size of a car. Everything after that was like driving an apartment building around by comparison. I was unaware that the Gemini computer had automated rendezvous capability, thanks for the detailed demo.

[@nitehawk86]

And it had ejection seats :) There was a version of it that was going to use a paraglider to guide itself to the ground instead of a splashdown. Theres an example of it in the Udvar-Hazy center.

[@anony3615]

imagine going into a timeship and bringing 2023 computer tech into this era. like being a hero plugging in a solid-state drive microsoft surface laptop 5 that weighs less than 4 pounds into gemini. the apollo 11 lunar landing having no memory or processing issues and landing automatically without sweating the pilots counting down the seconds before needing to abort.

[@rogervanbommel1086]

⁠@@anony3615 I mean, we’ll see, artimis 3 will be going to the moon soon, will it be smooth or not, one way to find out

[@arctic_haze]

Yes, the later spaceships were more like houses because only homeless people live in cars.

[@framegrace1]

It didn't had automated rendezvous capability. Scott just said the computer was not able to directly control anything. Just display information.

[@allenvaughan1]

Scott, my Dad was one of those engineers on Gemini. He and Gus Grissom were best friends, and Dad was his lead engineer on both of his flights on Mercury and Gemini. Then, for the third (and final) time, we moved back to St. Louis, where Dad was assigned to the fire control system on the F-4. A month later, Gus died (along with Roger and Ed) and EVERYTHING in our family changed that night, January 27th 1967. Dad stopped encouraging me with my excitement over anything-science-space-aviation. And when I mentioned that I wanted to get a job at the local airport and learn how to fly, he put his foot down and said "No!" I obeyed him.. but I sure didnxt want to. I still won the City Science fair in 1977. And in college, I took Chemistry I (as a business major!), never went to class, never bought the text book and made straight A's on every test. YET, the professor gave me a B!!! I complained to him as to why did he do that.. and his response was my "apparently lack of initiative" that I didn't take the class seriously, and so he didn't take me seriously either. Oh well...sometimes, you can't please anybody!

[@mrs6968]

As Ricky Nelson sang you can't please everyone so you gotta please your self Thank you for this beautiful comment I have a question before the tragic loss of Gus did your father have any great story or memory he shared with you about him? If you don't mind one last question what was the hardest yet best decision you ever made in your life? P.s if you don't feel like responding then no pressure honestly.. I just couldn't help myself from asking you these questions

[@kindlin]

The curriculum should be detailed ahead of time. They can have a 10% participation grade, if they want (at least, that's something I've seen), which will suffer if you miss too many classes or don't go to labs or whatnot. If your grade was just homework/midterm/final and you aced them all, then your grade should reflect that.

[@allenvaughan1]

@@kindlin This was the spring of 1979. You don't know what you're talking about. And, to top it all off, the prof WAS FROM IRAN! I never went to class...only the labs. My senior year in high school I was selected as the "Lab Technician" and TAUGHT the Chem I & II labs to the 10th and 11th graders. So, I'm telling you the truth, and have the history of success behind me to prove it. These days I'm studying heliophysics--every day.

[@allenvaughan1]

@@mrs6968 Gus nd Dad were really close. When we were back dosn at the Cape (living in Cocoa) Gus' wife and family were down there as well. Dad invited Gus over for supper, Southern style. (Gus was from Indiana.) So, he and his wife came over. I had to sit with my brother at a fold-out table. But I got to spend a few minutes before and a little bit after supper talking with Mr. Grissom. Dad and Gus put in a ton of extra hours on the gimbal mockup that was in one of the hangers at the Cape, as Gus wanted to learn how to fly the space craft. It turned out to be a good thing, because the programmed retro burn was so far off that had Gus gone ahead with it, the splashdown would've been over 180 miles from the intended point, close to the carrier. Gus, however, "flew" the craft and was able to shave off 120 miles from the error. Mr. Craft was embarrased at what happened according to Dad, who often said often that he respected Chris, he didn't like it when Mr. Craft started his cursing rampages during rehearsals! Chris once did admit that they forgot to account correctly for the Earth's rotation--but only once. And he was proud how Gus flew the reentry. Probably the saddest day of my Dad's life was January 27th, 1967. We were living in a small apartment, just a block away from my elementary school on Natural Bridge Road, and maybe a mile or two from Lambert Field where Dad worked. It was pitch-dark at 5pm up there! And nothing for me to do but whatch TV. Geez, i can't remember what was on now. But I remember the live news flash, and my mother running into the living room from the kitchen (she was making supper--shit! I remember now!! I was busy making B-52's out of Lincoln Logs, and putting blue tin foil on the tail of the "American" B-52, and red tin foil for the USSR bomber! (The colored tin foil came from the chocolate candy wrappers left over from Christmas stockings!) For many minutes, my Mom couldn't stop gasping as the news trickled in of what was going on down at the Cape. Then, the phone rang. It was Dad. He was coming home. After a few minutes of listening more, we knew that the fire had killed all three of the astronauts. Mom was crying. And when Dad got home, Mom ushered my brother and I into our bedroom, and she gave us stern instructions to not-say-a-word. I was starving in there. But, I could here my Dad crying in the living room. He cried for two hours straight. It was awful. Just plain awful. Lance and I finally got some food. But right after that we went straight to bed. I usually would see Dad leave for work in the mornings. But the next day, he was already gone. He was back McDonnell, probably commiserating with the other engineers that had survived all of the layoffs and got reassigned in St. Louis. Dad pushed through some major changes to the Phantom's fire control system, to the point where he got reassigned to a dream team of other engineers to work on this super secret project, that for the next two years he couldn't talk about. It was the F-15 Eagle! The hardest best decision I ever made? Hmm.. that's pretty personal. But I'll tell you. My freshman year in college (and I had a full-ride scholarship that paid my tuition, fees, room and board) I had two cousins who were firefighters in different municipalities around Birmingham, Alabama (we had moved down in 1974), and they had signed me up to take the firefighter Civil Service exam with them, UNBEKNOWNST TO ME!! They literally pulled me out of my dorm room bed at school and took me to the Boutwell Auditorium for the all-day exam. Well, I beat them both, making a 92.6% score, and ranked 90 out of 1600 applicants. Because of Affirmative Action hiring practices, it still took the City of Birmingham SIX YEARS to get to my number. Ridiculousness. All the while, I was praying while in school that I would get called up to join.. My father "forced" me to pursue a degree in business. But, you are reading the biography of a guy who should've received an A in Chemistry, but FLUNKED BOTH SEMESTERS OF ACCOUNTING...NOT ONCE, BUT TWICE--and still didn't drop out of school. You know what four F's does to a GPA? And psychologically, I'd never failed at anything. The third time I made B's, both semesters. So, I ended up with a BBA, and you bet I can read a Balance Sheet and a Income Statement. But the Birmingham Fire Department sent a letter a year after graduating asking for me to come and interview for the job. I accepted it, mostly as my perceived duty to serve, just as all the other men on my father's side of the family had in the military. Yet, tbere was something, or rather some-one who forced me to make the decision to move away from Birmingham, for good and forever. That was my brother, who just died back in January. But, he LOVED taking and selling drugs, and he had gotten involved with some drug cartel outfit out of Miami, after he had gotten drummed out of the Army in 1982---for starting a child prostitution ring while stationed along the DMZin Korea. (I couldn't verbalize that until after he killed my mother in 2019.) Lance used my parents, to the point where they both died of broken hearts...and broke. And it doesn't end there, because I have three civil suits I am pursuing against another cousin, the UPS and my mother's bank over in Bessemer, including a criminal case against that said cousin, for stealing nearly $20k from my mother, as she lay dying in a hospital. It's an awful situation I'm dealing with right now, since I am now tbe sole heir to practically nothing, yet I cannot close my mother's estate untill all of this goes through the court. It's a mess. But, I moved away from sadness, and for the most part have had a blast living in Atlanta.

[@Parc_Ferme]

These kind of comment that gives a human touch through the raw numbers of any huge achievement is amazing! Thanks for this story!

[@yrmoma]

Videos like this remind me of how very little I understand of the operational complexities of computers. I think most of us take for granted just how intuitive and powerful computers are these days. I remember when our family got our first Personal Computer back in the early 90s, so they've been a part of my life for a long time.

[@briandeschene8424]

When I worked in the mid-80’s on Digital Equipment Corporation PDP-11 computers for real-time process control in a steel mill, we drew up flowcharts like those shown here. I had taken an elective for drafting in high school which served me very well after I decided to get into programming. To this day doing work in Cloud architecture and design, I get better results than many because I still follow that disciplined approach with more front-end loaded design thinking long before contemplating one line of “code” (not always traditional code any longer).

[@connecticutaggie]

Thanks Scott. The NASA computer I remember most was the 4-Pi. My dad worked at NASA-JSC from 1968 to 1981 (I think). I was onsite at JSC many times and one time I recall getting to see a working 4-Pi. One thing I recall was how big the cooling system was - which they said was not a problem is space. Another thing I remember - for my birthday one year my did got permission for me to sit in the Pilot Seat of the Space Shuttle Flight Simulator. I think it was the MBS but I don't recall for sure. I do recall there was A LOT of switches.

[@ReentryAnOrbitalSimulator]

Awesome, thanks so much for using Reentry to show the on-board computer! Really appreciated! 🚀

[@flwi]

I'm a software engineer myself and I'm in awe by these early computer programmers. This all looks _very_ complex and I have no idea how they kept an overview of all those registers in their mind

[@frankhage1734]

This was standard for the era. It's like the C64 and the "peek and poke" instructions. You would register each address, mentally, to a specific function with practice. The manuals would tell you what each numeric register did. You could enter them by hand to test them out. It was easy for new programmers to figure out how to control hardware from software.

[@frankhage1734]

@@HollowVortex81 Modern programmers need to "refactor" their thinking. Old computers use to boot into a working command line within 1-3 seconds. It often takes Forza5 over 45 minutes to load and be ready to play, even over 1Gb/s connections. The 3 minute load times for games on C64 disk seems short in the modern era.

[@RCAvhstape]

@@HollowVortex81 I once learned to program a Motorola microcontroller, and though it seemed complex at first, once you learned the machine code and registers, etc., it was fun because you knew exactly what you were telling the machine to do. With a high level language like BASIC or C++ you are very removed from what the hardware is actually doing inside the plastic chip case.

[@PaulSpades]

They kept none of the registers in "their mind", they had each operation step written down, for all expected and emergency operations. Sure, they might have remembered some quick number sequences from training and simulation, but the standard procedure was: open up documentation and check twice before input, maybe even confirm with base ground beforehand or let them upload the instructions themselves.

[@jessepollard7132]

practice. same as now. IT is also why higher level languages were created.

[@harlanbaker7476]

I thought it was pronounced Gemini not Gemini

[@Hackanhacker]

:D

[@olasek7972]

Gemini not Gemini 😂

[@Dreddip]

Nope, Gemini. For some reason people think Gemini but if you ask people that were there it was Gemini. Whenever I hear Gemini I have to correct them to Gemini. Perhaps someday people will learn to say it Gemini instead of Gemini 😂

[@FastSloth87]

If you watch the NASA people talking about it they will actually say Gemini.

[@olasek7972]

@@FastSloth87 don’t you guys see absurdity of this conversation, Gemini versus Gemini, A versus A, etc.

[@joelclifton6312]

Imagine spending 2 weeks in that spacecraft. I know I can't.

[@maksphoto78]

When the capsule was opened back on earth, it smelled very bad inside.

[@incription]

this dude just gave up the opportunity to go to space

[@alanholck7995]

Even more difficult, imagine spending 2 weeks in there with Frank Borman. Jim Lovell deserves a medal for this.

[@5Andysalive]

Well more to the point in a extremely tiny spacecraft. The Apollo command module was already a big step up in size. And everything else.

[@maksphoto78]

@@incription In that particular spacecraft, for 2 weeks. I wouldn't either. The ISS is much spacier and comfier.

[@theharbinger2573]

Lets hope Curious Marc can get his hands on a Gemini computer some time. Thanks for the video.

[@christopherlawley1842]

Ooo yes.

[@glennpearson9348]

So much fun! Thanks for the tour of the Gemini computer, Scott. You make flying, flight, and orbital mechanics so enjoyable! Love your work.

[@Not-THAT-ChrisPratt]

Great video! You covered two of my favorite topics: Project Gemini and early computer history. Outstanding!

[@aemrt5745]

Gemini is my favorite classic space vehicle. It pioneered a lot of space travel we take for granted. Plus I love the fact that they used a ballistic missle that gave one hellova ride!

[@localroger]

In 1981, at the age of 17, I was part of a small group that was allowed to tour the Gemini ground system and they opened the locked gates for us so we could poke around behind the mainframe computers. Those were all powered by vacuum tubes and used delay lines, because they didn't need to fly. It was an awesome lesson for this young computer geek who was educated on integrated circuit based microcomputers.

[@jessepollard7132]

one problem with audio delay lines is that they are subject to data corruption caused by simple vibration.

[@localroger]

@@jessepollard7132 Yes, there were also calibration and temperature issues. The only good thing you could say about delay lines was that they were the least terrible solution anyone had come up with until core memory was made practical.

[@jessepollard7132]

@@localroger flying spot scanners were better.

[@MrAltairantares]

Always fun to watch a Manley video together for the first time with everyone else!

[@SeanBZA]

A lot of very bespoke computer designs were around before the microprocessor came along and guided them into a few very rigid areas. Especially those that were made from discrete logic, and where the designers went and made it with instructions they needed, and little more, and where your software and hardware were very tightly bound. Designed for the purpose, and then made to be as compact as possible, with, in that era, as few transistors as possible, because they were both very expensive, and also not as reliable as diodes. So you had a lot of diode logic, with transistors scattered around where absolutely needed, to act as inverters and regenerate the logic levels. Many of those designs were translated into early IC based systems, and they often used EPROM to do complex functions, like a lot of glue logic, and also to store tables used in math, so as to simplify multiplication, giving you the ability to have 2 5 bit numbers be multiplied together, to give an 8 bit output, in a single clock cycle. Used a 2708 1k EPROM, holding the decimal number table, and allowing you to do multiplication in a few cycles through the table per digit.

[@musaran2]

This is basically the description of an ASIC.

[@SeanBZA]

@@musaran2 True, and ASIC came out of wanting to reduce logic down from multiple boards to a single chip, to save cost and improve speed. Internally you either have basic blocks you stitch together, or have a full custom design.

[@lawrencedoliveiro9104]

We still have custom computer chip designs. You can put together a bunch of building blocks (e.g. a RISC-V CPU core, some RAM, some EPROM, some interrupt lines, maybe a display controller or Ethernet or Wi-Fi or USB or whatever), and a fab will do a run of chips for you. There might be a minimum number of a few thousand units or something like that.

[@SeanBZA]

@@lawrencedoliveiro9104 To run a run of them, using existing masks, the quote came to $10 per transistor, with a lead time of 18 months, and a minimum order quantity of 100k units. I needed 2, so went through the pain of putting in the paperwork, to have a common part substituted for this obsolete superceded transistor. The 100k 18 month lead time though is pretty much industry standard, unless it is for something like a sea of gates ASIC, where you only pay for the final metal mask, and run off a existing batch of nearly fully made wafers, where you will get 10k units, 100 wafers, one carrier full, run with your mask, processed and packaged for you. Make sure you got it right, because they only will do a basic wafer test to see if it responds to signals, and is not shorted too badly. Then it can be as low as 6 weeks, though you will pay.

[@lawrencedoliveiro9104]

@@SeanBZA When did you do that? I look at something like SiFive, and they claim they can put together a chip implementation for you within weeks.

[@w9gb]

Scott - Thank you for covering the Gemini capsule computer. At least 25 years ago, the National Air & Space Museum had a small exhibit area on the Gemini program, as well as the computer your video discusses. The exhibit noted that developments with military programs (planes, ICBM) were leveraged by the contractors (IBM, etc.).

[@MrJest2]

My father was hired straight out of college by IBM, sometime around 1958 or so. He was a mathematics major, and as a kid I remember these "math flow" sheets at our house occasionally, and much more frequently when he'd work on a weekend and take me to work with him (my mom worked in a hospital, and she didn't always have a M-F type schedule.) Man, that chart brought back a lot of memories... 🙂

[@silverc4s146]

Scott, I was an engineering tech at Texas Instruments in this era, and my group was building and doing the reliability testing on the Germanium small signal transistors that IBM purchazsed to build this computer. They were very expensive, because hours of burn in, read and record data were made for each device. Failure was not an option, as they would say. TI has purchased this Ge technology from IBM a few years before I joined in 1966.

[@mysock351C]

Hearing how the computer works reminds me of old GM ECUs used in their archaic CC-Carb and TBI applications. The calibration and part of the operating system was on a removable ROM module and the rest was on an OTP PROM and inside the code would toggle between the two based on the address bits similar to how it’s done here.

[@mycosys]

segmented memory is really common. Most of those systems had harvard architecture processors like the 8051that required separate memory for program and data.

[@KarldorisLambley]

4.00 ish - glass delay lines. i am blown away by such a thing. i thought core memory was bonkers, but turning data to sound to slowly send it down glass is utterly crackers!

[@jessepollard7132]

not any worse than the faster flying spot RAM used - a CRT with a camera in front. The RAM was implemented via the fade time of the phosphor CRT. 4K bits per image I think it was.

[@georgegherghinescu]

Great stuff Scott! The early space computers kind of remind me of very early TI and HP programable scientific calculators. The early TI SR's had a program called lunar lander where you had numbers showing altitude, vertical speed and remainig fuel (I think) and you made burns to slow down by imputing numbers.

[@bryanvogt3371]

HP had a similar program. It was my favorite to program (49 steps available!) and run on my dad's HP-25. Never managed a perfect landing (0 delta V), but came close a few times.

[@lawrencedoliveiro9104]

11:49 The legendary Seymour Cray had a simple solution to the problem of divide operations taking longer than multiplies in his supercomputer designs: he didn’t have a divide instruction at all. Instead, you had to multiply by the reciprocal of the divisor. He provided a special instruction for computing the reciprocal; the first execution of this instruction produced an approximate result which was lacking accuracy in the last few bits, so you had to execute it a second time on the output from the first time, to get the fully-accurate result. The assumption, I guess, was that you would tend to do a lot of divisions by the same divisor. Also you could skip the second iteration if you didn’t need the full accuracy in the result.

[@jessepollard7132]

It was fast to multiply. creating a reciprocal was easy just negate the exponent. I don't remember any issues with having to do it twice unless you were trying to get a double precision result.

[@lawrencedoliveiro9104]

@@jessepollard7132 From the Cray-1 Hardware Reference Manual (published 1977), page 3-28: “The division algorithm that computes S₁/S₂ to full precision requires four operations: 1. S₃ = 1 / S₂ -- Reciprocal approximation 2. S₄ = (2 - S₃ * S₂) -- Reciprocal iteration 3. S₅ = S₁ * S₃ -- Numerator * approximation 4. S₆ = S₄ * S₅ -- Half-precision quotient * correction factor The approximation is based on Newton’s method. The reciprocal approximation at step 1 is correct to 30 bits. The additional Newton iteration at step 2 increases this accuracy to 47 bits.”

[@StevePemberton2]

In the late 1960's or thereabouts my father brought home an adding machine from work, I think to finish some type of project or something. It was the first adding machine that I had ever seen or used (handheld calculators were about ten years away). I clearly remember that it only added, subtracted, and multiplied. It came with some type of card with reciprocals on it for division. Not sure if the reciprocal card originally came with the adding machine or if maybe there were generic cards available since I'm guessing this type of adding machine was somewhat common. I looked on eBay and there are some Olivetti adding machines that look similar to to what I remember. And I remember multiplication wasn't as simple as just pressing an "X" key as there wasn't any. I notice on the photos of the Olivetti's that they have a switch for multiplication, i.e. you turn multiplication on or off with a switch. That's likely how the one that my father brought home worked. I seem to remember that multiplication was just multiple additions, so the switch was just a convenience, you turned the switch on then pressed say the number 7 and then pressed the + key and it would crank away as it added the previously typed number seven times. Something like that anyway.

[@lawrencedoliveiro9104]

@@StevePemberton2 If you’re interested, look up the Friden calculators from the 1940s/50s. They could do multiplications and divisions by repeated addition/subtraction. Later models were electrically-driven.

[@holokaisail]

Thanks so much for sharing this extortionary space history with us this Scott. I've been fixated and fascinated with the relatively simple and basic computers and extraordinarily written code used in the Apollo program to help get us to the moon and back. But I hadn't heard about this extraordinary earlier Gemini computer system. I feel a bit blessed that my own introduction to computers was with just using basic DOS syntax and commands. I find it quite refreshing to understand that our first pioneers into space weren't just 'spam in the can' stick jockeys, but also had to understand how to effectively use such a very primitive, yet pretty advanced for the time, technology.

[@gordonstewart5774]

Cool! My Dad built satellite "On-board Processors" (NASA didn't allow them to be called "Computers") at Goddard in the early 60s. He became an expert in Radiation testing, help create the NSSC (NASA Standard Spacecraft Computer), and was Mission Operation Manager for the first repair mission in space (Solar Max).

[@TastyBusiness]

Man, this is just hitting all the right notes for me. Gemini? Check. Computer history? Check. Playing reentry? Check.

[@DrMemory99]

This is fantastic! Wish Id known some of this during the missions to give me a better appreciation earlier.Thank you for this detailed bit of history. Incredible. My career was spent on the Space Shuttle and we often dont realize or appreciate the evolution parts of the new designs.

[@bruceadler-9410]

The Gemini IBM-designed general-purpose digital computer was preceded by the, MIT-designed, IBM ASC-15 general-purpose digital computer designed for the Titan II rocket. Wikipedia says the Titan II first flew in 1963, about a year before the April 1964 Gemini 1 flight (which used a modified Titan II as the launch rocket). But the IBM ASC-15 was still not the first fully-functional general-purpose computer to fly in space. The first fully-functional general-purpose digital computer in space was the Minuteman 1's guidance computer, the Autonetics D17B (interesting side note: in the late 1970s a friend of mine rescued a 15-year-old non-functional D17B from the UCLA School of Engineering scrapyard and turned it into a pedestal for a glass-top coffee table - it was about 2.5 feet in diameter and about 1.5 feet high). The Autonetics D17B was the first general-purpose digital computer in space but it was preceded by a couple of special-purpose digital computers (ie not a general-purpose digital computer) . I think the MIT-designed Mk1 digital guidance computer used on the Polaris 1 submarine launched ballistic missile might have been the first special-purpose digital computer. It was a digital differential analyzer which implemented the Q-guidance calculations developed at MIT. You could argue that those computers flew on ballistic missles that (unlike the orbital Gemini 1 computers) didn't orbit the earth. But I suspect there were also general-purpose digital computers on some of the NRO's classified Keyhole spy satellites (possibly supplied by IBM), that were orbited before Gemini 1's 1964 launch. If so, then the Gemini computer wasn't even the first general-purpose digital computer to orbit the earth.

[@bruceadler-9410]

This D17B unit is missing the IMU gyroscope platform which should be in the middle of the card cages: kzbin.info/www/bejne/gWKcnISehNZ7ic0

[@workonesabs]

The last bit was also a Parity Bit, basically error checking, which in this area is critical, that any corrupted data is recognized, ignored and resubmitted until the parity bit matched the data.

[@DavidSmashGames]

Those flow charts are still used today in programming or at least I was taught them in college very cool!

[@michaelmoorrees3585]

15:00 - My first electronics job, in the 1970s, was as "general flunky", which included being that small company's draftsman. I drew up both schematics, and flowcharts (of computer subroutines). I have a good drawing "hand", and that company designed early circuits, and code (90% of the actual work) for early 8-bit microprocessors (8080, 6800, ... ). I also ran errands, such as get the engineers lunch, and wait in the gas line, to fill the boss's car, during the oil crunches, of the 1970s.

[@russellfitzpatrick503]

Ahhhh! Flowcharts ...... How lovely they were, back in the day (works of art almost). Spent hours over the things, mid 70s and beyond. Many thanx for the memories

[@RV4aviator]

Superb Laddie !!! All the Space nerds out there get excited about the AGC . And rightly so...! But the Saturn V IBM IU , and the Gemini computer get looked over, so thank you. The Gemini spacecraft was designed with heavy emphasis on Test Pilot functionality, mainly Gus Grissom. As one of the Gemini Project goals was rendezvous and docking , it became apparent that a computer was necessary, as eyeballing your target in space using aerodynamic techniques wouldn't work. In orbit the opposite approach was needed.

[@NickRedstar]

I’ve got an idea for a video. Look into who built the space suits for the moon missions. It’s a great story.

[@rayoflight62]

There was a multi-part documentary series - now no longer available on YT - called "Moon Machines". One of the episodes was dedicated to the development of the lunar suit, and the strange rivalry between the two companies who developed the suit, with NASA mediating between the two...

[@jellyfishattack]

Gemini spacesuit zippers made my scuba drysuit possible.

[@NickRedstar]

@@rayoflight62 I watched the doc. That’s where I got the idea for the video.

[@lawrencedoliveiro9104]

That was the one part of the Apollo program with probably the most women involved.

[@EveryoneWhoUsesThisTV]

I still have a kid's book that reliably informs me that 16KB of memory is all a home computer user will need.... :) Moore's Law is nuts...

[@Asterra2]

But imagine how many readme files you could store all at once with that kind of upgrade.

[@arctic_haze]

My PhD supervisor could not understand why I wanted to own a computer. For him computers were mainframes.

[@attilavs2]

Now 16gb is the new standard :-)

[@OrenTirosh]

@@attilavs2 you mean the standard for mobile phones, right?

[@attilavs2]

@@OrenTirosh No was talking about *memory* aka ram, not *storage* aka rom

[@Greenmachine305]

Super facinating. How people contest the moon landings baffles me.

[@schmetterling4477]

Most people are idiots. We are where we are because there are always a few who aren't.

[@Arkanic]

Gives a whole new meaning to digital archeology... It's wild to me that we've lost so much information, maybe at the time they thought computers of this design would become commonplace and exhaustive records would be unnecessary.

[@personzorz]

Or they didn't care about lots of people being able to understand them, they were just making something that had to do a specific job

[@heaslyben]

I love those flow drawings! To me they express the joy of working together to understand a problem. Very neat. Also they look like alien transmissions out of Contact.

[@notjackschannel5380]

Graphical communication, whether it’s a part, assembly, program logic, or failure mode analysis, is always a thing of beauty.

[@andrewnorgrove6487]

Great looking Simulator with early access and VR even better )) thanks Scott

[@RobinWootton]

Thank you for studying this for us. I don't know what was most astonishing, to build it or to fly it! I was a CAD draftsman, now a software engineer, so the designs at the end were a very special blend to see.

[@ryanhamstra49]

Oh man, this would be so cool in VR!! If the people who made this are here, please make for oculus!!

[@bujin1977]

The VR version of this game is already being developed. It is possible to play in VR at the moment using a beta version of the game. I found it a little bit fiddly to get it to click on the right place and often flicked the wrong switch, but hopefully that will improve in time. I've only tried the Mercury missions in VR so far.

[@TimPerfetto]

@@bujin1977 Yeah you better stop clicking things I am getting really sick of it idk why you are ruining his life

[@ReentryAnOrbitalSimulator]

VR is indeed in development! The old VR implementation (all crafts) is available on a dedicated branch while the new in-dev implementation is available in the alpha-features section (Mercury only so far) :)

[@ryanhamstra49]

@@ReentryAnOrbitalSimulator sweet, thanks!!!

[@unfa00]

I imagine sitting in this cockpit and knowing that if I make a mistake that might cost me and the other guy our lives. These people must've been the best around.

[@Umski]

It’s mind blowing that these guys designed and drew up this stuff all on paper and then tested robustly so many decades ago - even as an EE that dabbled with assembly instructions on x86 many moons ago and have some appreciation of computer architecture this is humbling 😊

[@jaapodac]

I hope this video makes its way to a museum someday, that's how good a job I believe you did giving us a flavor of this era in spaceflight history.

[@TeagueChrystie]

I mean, yeah, the word is "gemin-eye," but a lot of the astronauts said "gemin-nee" so it feels old fashioned and cool. Like aeroplane, every now and then.

[@jmdibonaventuro]

I actually have a test report from a Gemini-Titan Flight. Had a family member who was an electronics engineer on Gemini and Apollo Black Ring Computers. Thanks for shedding light on these often overlooked but interesting systems!

[@dblumentr]

Awesome history lesson on Gemini, its hard to find information like this on Gemini. Ed White's EVA was the first NASA mission I remember well. My Dad would wake me up to watch all of them back to Mercury missions.

[@nathanscheller5170]

Your ability to describe technical and scientific data for the Lament is truly unmatched.

[@FotosbyFrankie]

Scott, this was absolutely fascinating. Gemini (THANK YOU for pronouncing it correctly!) has always been my favorite capsule of the three that got us to the moon…. Mainly because it provided such a vital bridge between the most primitive and the “most complex”. Thank you so much for giving me another reason to marvel at this remarkable piece of machinery. Your videos always put a smile on my face. Thank you!! 😊

[@julianskidmore293]

I'm really glad that Gemini is supposed to be pronounced as Jemmin-eye rather than Jemiinnee, because that's also the normal British pronunciation (& I'm a Brit). But the question is why, did NASA choose that pronunciation too?

[@jaycee330]

@@julianskidmore293 Because it matches the Greek word Δίδυμοι, so really everyone is pronouncing it wrong anyway (vihveemee).

[@hjalfi]

Back at the Apollo 11 anniversary, I spent some time with VirtualAGC and wrote a lunar lander game which would run on the Apollo Guidance Computer _on_ the lunar lander. It was a fascinating experience. In many ways it felt quite modern, and was completely unlike the huge mainframes that the original programmers actually used to assemble the original software (Luminary for the lander and Colossus for the command module). But then in other ways it was utterly bonkers, like the 1s-complement arithmetic which meant you had two distinct zeroes, the 15-bit words, and the very strange instruction set which with the hindsight of fifty years experience has some _very_ badly designed opcodes. But there is a dedicated radar interrupt, which makes it all worth it. Also: "Pieces of nine! Pieces of nine!" "Ah, yes, a parroty error."

[@JossWhittle]

Knuth's The Art of Computer Programming - vol 1 released in 1968 and defined a hypothetical computer architecture and assembly language based on current trends and Knuth's own ideas. It used 31 bit words composed of a dedicated sign bit, followed by five 6 bit bytes. And it had more variants of the JUMP instructions than a basketball coach. Truly a wonderful (and silly) architecture to study and a true product of its era.

[@lawrencedoliveiro9104]

It was a product of its era: Knuth was trying to be as architecture-agnostic as he could, because “decimal” computers were still a thing. I think in the later editions he threw all that rigmarole away.

[@jessepollard7132]

Assembly language always had more words for instructions - JUMP, JUMP on overflow, jump with/without offsets to add to the PC, jump on carry set/clear, then there would be other variations branch (offset always less than 128) with carry set/clear, subtract one and branch...

[@adamdejesus4017]

Solid state core memory and tape drives like these didn't die out until (at least) 2000. Granted by that time the hardware was more sophisticated and had more capacity. When I started flying for the military in 1998 we operated the Litton L-304 with several 16K core memories using 32-bit words. This made it capable of running programs with easier user interface but you still had to know how to talk directly to the computer using thumb dials and codes, to load the various flight programs from tape, or troubleshoot the computer hardware. Everyone who operated it had a page or two of codes in their pocket, to either give instructions or read back information. We were also still using punch cards. And we didn't abolish the floppy disk until 2010.

[@marktowner9172]

Fun fact, the Shuttles did not have hard drives. They used core memory. HDD Zero G and High G concerned NASA. I think Dragon only has SSD memory. Nothing mechanical

[@mrs6968]

Woah you mean to tell me the united states military was still using the humble floppy disc until 2010???? I'm not calling you a liar I'm just shocked in disbelief is all. Second question what was your favorite part of serving in the military? Lastly thank you for your service

[@attilavs2]

@@mrs6968 They store up to a whopping 1.44MB, i don't see why you would need more And i mean if it ain't broke don't fix it

[@sundhaug92]

@@attilavs2 Less even, since at least the Minuteman systems were on 8" drives

[@mycosys]

@@mrs6968 Japan is only just moving from _requiring_ floppies for official communications.

[@mikeymcginley]

Dude, I'm a pretty solid dev, but you make me feel like a child with videos like these. Geeeez.

[@mikeymcginley]

Correction... The SIXTIES are what makes me feel like a child.

[@MD.ImNoScientician]

A brilliant piece of history there @ScottManley. Thank you for the recap.

[@Jackissimus]

I am again amazed that my KSP experience gives me just enough knowledge to understand most of this. The guys at Squad really made an awesome job making this approachable.

[@LLH7202]

This is one of the reasons why Gemini was leap ahead for the US space program. Although looking like a larger version of Mercury, also built by McDonnell, Gemini was a true pilot's spacecraft. The Soviet Voskhod was merely a modified Vostok and had no orbital rendezvous capability. The Soviets couldn't compete with Gemini.

[@johannesgutsmiedl366]

that's a bit of an unfair comparison though, the voshkod was indeed simply a modified vostok intended only to snatch the "first multi crew" and "first spacewalk" trophies in the space race which it both successfully accomplished and it was retired by the time gemini had its first crewed flight... meanwhile while gemini was the main technology testbed for apollo the soviets were working on the far more capable soyuz (there's a reason why that thing still flies today!). Gemini definitely was a major leap for the US space program, but it was never a competitor to voshkod (nor was it intended to be).

[@LLH7202]

@@johannesgutsmiedl366 You are correct. The point I was trying to make is that the the Soviets were still trying to capture "firsts" to show they were ahead. Meanwhile NASA had become laser focused on the moon goal and Gemini was an important step in that goal. Rather than merely try to get ahead of the Soviets they had their own objectives for each mission. In some ways (not to take anything away from Alexei Leonov's accomplishment of the first EVA), the Soviet EVA on Voskhod 2 was more a reaction to NASA's stated goal of doing it on upcoming Gemini 4 to get there first.

[@johannesgutsmiedl366]

@@LLH7202 yeah but tbh the soviets were focussed on the same goal by the time gemini started flying, I think the amount of effort spent on voshkod is in no way comparable to what the US put into gemini (and I doubt that NASA voluntarily gave up on those "firsts", mercury just wasn't suitable to be modified into a multi crew vehicle like vostok and gemini wasn't ready in time). Given the limited resources the soviet lunar program had I'd say going directly to soyuz after vostok/voshkod was definitely the right move, though by then there was no way they could compete with the sheer amount of money the US was willing to throw into the apollo program.

[@HDRW]

When I was learning to program, in the early 70s, we always had to draw a flowchart before ever writing a line of code. That meant you could check the logic flow much easier than trying to debug the code, meaning you knew it would work, you just needed to write what was in the flowchart. I even had (may still have somewhere) an IBM flowchart template! Thanks for reminding me of that...

[@RegebroRepairs]

Gemeni? Gemenaj? Gemeno? Gemenwhat? Gemenaaaah! 39 bits is clearly based on "Well, we can't make it faster than 7kHz, so let's just squeeze in as many bits as we can".

[@blairseaman461]

Those Math Flow Diagrams were definitely created on a drafting board. It's a dying art.

[@paulhightower9086]

Thanks, Scott. You and the family have a great Memorial Day!

[@frankgulla2335]

Great summary of the solid-state computer used in the Genimi capsule. Thanks, Scott

[@lawrencedoliveiro9104]

15:45 The IBM computer that controlled the Saturn V was a hybrid digital/analog design: the digital part wasn’t fast enough to make corrections to thrust magnitude/direction etc in real time, so that was left to the analog part, while the digital part just computed the direction the rocket needed to go. (I think it could only come up with new numbers once a second, or something of that order.)

[@somestarman892]

Great video as always!

[@woodypigeon]

To a non-engineer such as myself all this is bewilderingly complex.

[@aemrt5745]

Heck, I am an Engineer who does not do programming and computer design and I find it bewildering complex!

[@MCsCreations]

Fascinating indeed! Thanks, Scott! 😊 Stay safe there with your family! 🖖😊

[@DACFalloutRanger]

My god, old computers were a real feat of engineering.

[@DaveWhoa]

my brain went into an infinite loop when i read "39 bit". i need a power of 2 damnit!

[@sundhaug92]

I mean the AGC is only slightly 2^n, as it uses a bit for parity

[@Rob2]

Remember every extra bit costs hardware to implement it. They probably had done a study to determine the precision required in calculations, someone arrived at "one in 10 million", they doubled that for safety and rounding, added a bit for sign, and arrived at "we need 26 bits". Then through the architecture described in the video they arrived at 39 bit words. Sure, you could round up the 26 bits to 32 and then get a 48 bit word length, but that would mean you need to implement 9 bits that you do not really require. And your computer probably will use 23% more power, will be 23% larger, 23% heavier than what is required for the mission.

[@lawrencedoliveiro9104]

There were quite a variety of word lengths in the days before byte-addressability became the standard. DEC’s first machine, the PDP-1 had an 18-bit word length; their very popular PDP-8 range used 12 bits (awkward to program, but cheap for those days); and their big “mainframe-class” PDP-10 had 36-bit words. I think the CDC 6000-series supercomputers, designed by the legendary Seymour Cray, had a 60-bit word length. The guys at AT&T Bell Labs who invented Unix did their first prototype on an old PDP-7, another of DEC’s 18-bit machines, that they had lying around. That proof of concept allowed them to get the funding for a nice new, 16-bit byte-addressable PDP-11. And the rest, as they say, is history.

[@jessepollard7132]

not any more pecular than 36 bit or 18 bit systems (which the PDP-10 was, as the predecessor to the DEC 10s and 20s.).

[@DaveWhoa]

ok I will reduce my request of a power of 2 ..... to an even number of bits

[@richb313]

Scott RPN was tough for me this is beyond tough to nigh near impossible to comprehend yet the guys who actually flew these things had to understand it thanks for showing this to us.

[@Allan_aka_RocKITEman]

Great video, Scott...👍

[@rhorho2]

Cool sim! Regarding pronounciation of Gemini, in old news footage from the time it’s pronounced as ‘Geminee’, so you could argue that is the correct way?

[@KeritechElectronics]

Lovely flowcharts indeed. Thing of beauty, joy for ever.

[@sikhswim]

Thank you for this. This is incredible didnt know I could train to be an astronaut on original systems!!!!

[@BarryRowlingsonBaz]

Am amazed there's no source code, I just watched a Curious Marc video where Mike bought an early Apollo AGC source code listing at an auction, had it transcribed, ran it on the emulator, and then reconstructed the version flown on Apollo 10 (the only other known copy being in orbit with Snoopy, the lunar module) by interpolating and comparing checksums.

[@sundhaug92]

May have to do with timelines and who did it. AGC software was MIT Draper labs. We don't for example have the software for the LVDC (although it's theoretically possible to read out from the cores various museums have, you'd only have one go at it)

[@BarryRowlingsonBaz]

@@sundhaug92 I can imagine the response if you went to a museum and said "Can I un-knit that rope memory?" - it'd be like asking to melt down Tutankhamun's mask.

[@lawrencedoliveiro9104]

There would be non-invasive ways of reading out the memory state, with external passive probes or something.

[@Miata822]

I thought the Gemini program was cool, often forgotten and underrated, but definitely owning the coolest booster engine startup sound.

[@PrinceAlhorian]

Whooop!

[@RRaquello]

I just missed Gemini. First flight I remember watching on TV was Apollo 7. But imagine a program with 12 flights in two years, one every other month, and each one with something new. Nothing that's done in space can ever match those days.

[@billlange9408]

Scott, I love your channel. One of my favorites to see a new video pop up for. This was no exception! I know it's a minor thing, but I'm curious as to your evidence for the pronunciation of Gemini? I'm not saying you're wrong by any means. I pronounced it like you do for the majority of my 42 years, but in the last decade or so, it's been a very popular trend to see YTers saying it Jemma-knee. When you listen to all the old recordings of the missions, it's primarily pronounced that way. Pete Conrad himself pronounced it like that as have many other astronauts. It's how it was pronounced in First Man and other historical recreations as well. To me, your pronunciation sounds better and is what I typically default to, but I'd love to hear your input and thoughts!

[@pjosephlthewonder5082]

Nice information on the once great and still relevant Gemini missions. I was many years back able to talk with a former NASA Engineer, forget his mane but he told us that the computer that was used in the Gemini spacecraft was about a powerful as that of the current basic calculators (vintage mid 1970s) and that they were slow to boot. The importance was they made the calculations and presented a solution. I was amazed and went into the US Navy to become an electronics type, worked in computers, navigation and comms in my years. I would love to see a schematic of this system. Peace

[@RRaquello]

I also got to talk with a NASA Computer Engineer once and he told me that the comparisons of an on board computer to a modern cell phone is misleading because all the heavy duty computer work was done by mainframes on the ground and the computers on board were mostly for timing and sequencing, so the computing power they had was all they needed. Obviously that's true because they completed the missions with what they had. He also said that the mainframes they had then could do the job now because 99% of the extra computing power they have now goes into creating the graphic interface and not the calculations needed for a mission like Gemini & Apollo, if all the graphics you were getting was green letters on a screen. I'm not expert at this stuff, so I don't know if he was being a contrarian old guy.

[@OGWhinnyBaby29]

Thank you so much for making this content. You are great.

[@radioactive9861]

Scott Manley, I think I speak for everyone when I ask this question: Can this game/simulator you are showing us execute the 'SCE to AUX' command?

[@DanielCharry1025]

Best CSM simulation out there is NASSP for Orbiter. Hope that we get a master series on that spacecraft.

[@ReentryAnOrbitalSimulator]

Hi! The game does indeed let you switch the SCE to AUX. In a multiplayer mission control session it can even break and you need to flip the switch to correct it. It will award you with the SCE to AUX achievement 🤓

[@radioactive9861]

@@ReentryAnOrbitalSimulator Excellent!

[@douggraham5082]

Scott, love the channel but you know as well as I do the program was called Gemini, pronounced "Geminee" and not "Gemin-eye." That was the official NASA pronouncement.

[@colinjohnson5515]

I find it funny how we discuss core memory requiring a write for each read as slow because the magnetic field is drained on a read. Well this happens in modern DRAM too but it’s a modernized system of course. DRAM stores bits in capacitors. So reading the voltage level drains the capacitor. Also unlike magnetic core memory capacitors drain over time so DRAM modules are constantly refreshing the stored values before the internal resistance drains the stored value down to zero. Imo the key differences are 1. Creating/draining/reversing a magnetic field takes more work than charging and discharging a capacitor this more current required and more heat to dissipate. Distance between physical bits in core memory have minimum size requirements before the induced field is too weak and also field to field interference causes issues. 2. Modern RAM has internal controllers that handle the write after read and refresh mechanisms at frequencies high enough that the cpu doesn’t see any difference when the blocking refresh operation is executing.

[@Rob2]

Actually, in DRAM the capacitor drains not from the reading but from the time you do not pay attention to it. So while the nuisance is similar, it actually is worse. Also because you will lose the memory on powercycle and often even on system reset.

[@cogoid]

@@Rob2 It is true about the gradual leakage, but the readout also temporarily discharges the cells. When a row of DRAM cells is enabled, the cell capacitance of each cell in the row is connected to that of the long readout line shared by all the rows in the block. This spreads the charge, and the voltage of the cell drops to a fraction of its initial value. Just after this, the sense amplifier gets enabled, and the way the amplifier functions causes the voltage on the lines to return to a fully charged or a fully discharged value, depending on the sensed state. The row can now be deselected, and the state of all its cells has now been "refreshed". Thus the entire readout process indeed does not discharge the cells. But during the process there is a moment when the cells are discharged into their readout lines.

[@jesseturnip]

I would love to have copies of those flow charts on my wall as artwork

[@dinofrangiamore]

Great history Scott, thanks!

[@GeneralJackRipper]

Scott, you can hear both pronunciation in archive material.

[@OnlyLightMatters]

The correct pronunciation is Jiminy : [HOUSTON, April 2 (UPI) -- Regardless of what the dictionary says, the Federal space agency's official pronunciation for its new man-in-space program, Gemini, is "Jiminy," as in "Jiminy Cricket."] Published the 2nd of April, 1965 by the New York Times. You can check with your own google research, when I put an external link the post is removed.

[@GeneralJackRipper]

@@OnlyLightMatters I'm sure the new york times means well, but when the actual people running the mission pronounce it however they like, then that is that.

[@justinscharf8838]

Love this game. Glad to see ot getting some coverage. Any chance you could run through some of the Apollo missions at some point?

[@philipegoulet448]

Just to let you know, the link to ibliblio in the description is dead!

[@kimkeam2094]

With all the tasks you have given yourself, how do you find the time to learn the codes and binary language, play the game, study for pilots license, communicate with family and run a KZbin channel!? I’m impressed!

[@ryanschweikhardt]

It would be awesome to quiz Jim Lovell with that game just to see how much he remembers after staring at that display for 14 days in orbit

[@CharlesP2009]

I've forgotten almost everything I learned about Commodore BASIC and MS-DOS less than thirty years ago. But then I didn't train and drill like he did for his missions so who knows. 🤣

[@ryanschweikhardt]

@CharlesP2009 I've been surprised by asking old mechanics questions on old stuff that they still knew like they worked on it like yesterday. I'd say there is a chance Jim still does especially given his crazy level of intelligence.

[@lordflashheart3680]

Exellent video Scott, thank you.

[@jim2lane]

Wow, listening to this takes me back to my assembly language programming course in college 😊

[@gregorylewis8471]

Those software flow diagrams were all done by draftsmen from the hand written input of engineers. I remember getting a new radar processor and all the drawings we got were Boolean. I worked on an emulator that emulated an IBM 1130. I was happy when I had a system that had a full 64K of memory. That meant I could load all of my punch card diagnostics at the same time! The company employed a few ladies whose job was to travel and fix core memory. Cool thing was I could start diagnostics on a system, shut it down, take it apart and ship it to another location. I would arrive put the core memory back in the same order, turn on the machine and viola! The diagnostics picked up where they left off!

[@jessepollard7132]

When I was working with navigation systems for ships that was the standard method of sending updates - load it in the lab, turn it off (carefully halt the system first), pull the core and ship it to the destination.

[@kobihersh]

a very interesting leason in history of space - Thank you Scott

[@jovangrbic97]

Did the computer actually control the burn/thrusters directly, or did it just show the crew 'numbers' and the crew physically had to 'hold a button' to keep the thrusters firing for the calculated amount of time?

[@jessepollard7132]

Only did that when in a manual mode. otherwise the computer did it.

[@bobdinitto]

This is quite a convoluted memory addressing scheme reminiscent of the PDP-8, and having "instruction segments" allowing 3 programs to essentially multiplex the memory is very unorthodox. But considering the state of the art of that time and the engineering challenges it's quite impressive.

[@lawrencedoliveiro9104]

The old DEC machines (from the same era) had that “page” bit (to select either “same page as current instruction” or “page 0”) but they also had an “indirect” bit, which meant that the word being addressed could hold in its turn a full indirect address. That seems to be missing here.

[@lawrencedoliveiro9104]

1:15 Fun fact: the first Apple Ipods (remember them?) had little Toshiba hard drives in them. Yup, spinning drives (I think 1¼” diameter) in a device that would be moving around a lot, kept in people’s pockets or purses, likely dropped and bumped a few times. And still keep working, without a bunch of engineers back at Mission Control continuously monitoring things. The market window for these tiny drives was brief, before flash memory completely took over from them.

[@RRaquello]

I still use one of those. Actually, I use three of them. When you press the button and it starts up, you can hear it spinning if you hold it close to your ear.

[@josephkanowitz6875]

ב''ה, IBM and Toshiba did a lot on these. Conveniently things get somewhat more rugged as the platters get smaller, though I've heard rigidity of the casing could be doom for the CF-sized models.

[@thesteelrodent1796]

Back when "computer" really meant "fancy calculator". Assume there was very limited error checking, since it was very difficult to do in those early computers, and at least on surface computers it wasn't done much as the operators were expected to know what they were doing. The "Verb" and "Noun" entries Mike talks about in CuriousMarc's videos about the APC restoration makes so much more sense with your explanation. The guys never really explained how the commands and memory was structured, but it makes sense if it's done this way. I guess it's similar to setting the memory switches on the old mainframes, where you had to manually tell it use the A, B, or C option when running the current program (the predecessor to modern command line options).

[@mycosys]

*back when computer meant 'woman who did the sums'

[@thesteelrodent1796]

@@mycosys true as well

[@trs4u]

@@mycosys They didn't have computims?

[@starbomber]

That math flow looks insane, but when I was studying computer programming we would use documents like that to visualize operations in object oriented systems.