- The Saturn V rocket
took humans to the moon for the first time, but the
humans didn't steer the rocket. It steered itself using a computer. - [Man] Tower, clear. - [Man] Gotta roll program. - A lot of the Saturn
V rocket was built here in Huntsville, Alabama,
otherwise known as Rocket City. And one of the really cool
things about living here is it's filled with aerospace
and computer engineers who love this stuff, so a
thing you can actually do here is pick up the phone and
call one of your friends and have them call their
friend, and before you know it, you're in a parking lot,
receiving a Saturn V memory module from a guy you just met, and he just trusts that you're
gonna give it back to him. This is 14 kilobytes of data,
which is really interesting because the same day I got this, I had Linus Sebastian
from Linus Tech Tips here. We were installing a server
that was over 100 terabytes. Now, millions of people look to Linus to understand more about
modern computing hardware, so I thought a really cool thing to do would be stop what we
were doing with the server and take a closer look
at this memory module and how it works. Let's sit back and watch
a modern computer nerd learn about the cutting edge
technology from the 1960s. I'm Destin, let's go
get smarter every day. - [Destin] Have you ever
seen a Saturn V rocket? - [Linus] No. - [Destin] Okay, do you
know what the Saturn V is? - [Linus] Yes. - [Destin] My daily
life literally revolves around the Saturn V. Like, that's the Saturn V peeking out over the trees right there. - [Linus] Oh, there it is. Hello. - [Destin] In the 60s, they
had just started building digital computers, and I'm
gonna show you the computer that they used to steer that thing. - [Linus] I mean, it's gotta be a bit of a terrifying experience having, like, the equivalent of a very large bomb strapped to your butt. - So this is the brain
for the Saturn V rocket. If you look up right here, this
is the instrumentation ring, and so they had computers
on here that were digital. This right here is the launch
vehicle digital computer. That is it. This right here is a memory module, okay? And if you look really,
really, really close, really close, you see
those little bitty rings? - Yeah. - [Destin] OK, look right here. Look at that. Do you see that? - [Linus] Holy smokes, so they're, it looks like zip ties on chicken wire. - [Destin] Okay, those are bits. Those are physical bits. So you see that screen? - [Linus] Yeah. - [Destin] These are wires that go down to these boards right here, right? - [Linus] Yeah. - [Destin] On each node,
you have an iron ring, and depending on how the
iron ring is magnetized, that's a one or a zero. That's how they programmed this computer. Seriously. So look at this right here. - So by hand. - [Destin] By hand, yes. - They threaded these wires through the, I mean, who has a steady,
I don't even think you can build one of these
today if you wanted to. That's incredible. - [Destin] So there's a
guy that worked on this in the 60s here. His name is Luke. - Yeah. - [Destin] And, you get ask
him all of these questions. - Fantastic. - I'm Luke Talley, and
at this time in 1969 I was a senior associate
engineer at IBM in Huntsville. - [Destin] So your computer
pointed the rocket? - That's right. - [Destin] Awesome. - We steered the rocket. So that's a memory module. - [Destin] That's a whole
memory module, yeah. - You musta shot somebody to get that. - [Destin] So how valuable
would you say that is? - Well, now this, ah, I
don't, I'd have no idea. You have to go to Antique Roadshow. This computer controls all the timing. Start engine, stop engine,
fire separation rockets, fire retro rockets, all this kinda stuff. It does navigation and guidance. You have stored in the memory a profile, at this point in time I need to be here, going this fast, going this direction. Now realize that this is core memory, so you have these magnetic cores, you have the wires
feeding through the cores, you push a current down through a wire, if you've got a wire, current's
going in that direction, the magnetic field is going
to be in this direction. If it's going this way, it'll be that way. Make that a one, make that a zero. There's 8192 of those on
this plane, all right? - [Linus] Yeah. - Then there's 14 of those planes stack up to make this module. This module is what you're holding. All this stuff now, the
drivers to drive this thing. - That's just to program
it as a one or a zero. - Because this is basically
an analog process. - Right. - I'm not writing ones and
zeros into a logic gate and storing them that way. - You're just sending a current -- - I'm actually having to
make, magnetize a core one way or the other. And then I've gotta read
it, and when I read it, I destroy the magnetization,
so I have to turn right back around and -- - Write it again. - Write it back in there,
so that it's not missing. - Oh, no! - So there's one of these in this, and then there's one of these now in each one of these blocks
on this wall over here. - [Linus] Got it. - So we have four, 8, 12,
16 thousand words of memory, another four, 8, 12, 16
thousand words of memory. Now when the Saturn's flying,
both of these memories are executing the same flight program. - [Linus] Completely in parallel? - That's right, and they're
comparing the outputs to make sure they're
getting the same answer. If they were to not get the same answer, go into the sub-routine and say, "I'm at this point in the flight, I got these two numbers,
what makes the most sense to keep using," use that
number and keep going. So your critical parts
are triple-redundant in the logic, dual
redundant in the memory. As I recall, during
all the Saturn flights, we had like, less than 10 miscompares, something like that. It was a very small number. - When you're building a rocket, you have some important parameters that you have to monitor. Power, data bandwidth, mass, volume, you have to manage these so
they don't get out of control. So you want a reliable
system, but at some point, you have to make a decision. How redundant is redundant enough? - Unreliability, that's the key, because the more of these things, the more core's you add, the
more of this stuff you need, the more unreliability
you add to your system, because sheer numbers of parts. - Right. - Luke is about to
explain what it was like to receive data from the
Saturn V via telemetry and then analyze it, and
I'm gonna let this play out, because I want you to
understand how repetitive and difficult this task was. Today we could do this
with just a few minutes and some spreadsheet
software, but back in the day, they were the computers. Like, the people were the computers. So I want you to see it through his eyes, through this historical
lens so you understand what it was like to
analyze the Saturn V data. - So did you pull the data
down while it was flying? - Things happen too quick in flight to. - [Destin] How do you know you had -- - We get the data back and then we ana, that was my job at IBM,
was we were analyzing the flight data to determine what worked, what didn't work, if it
didn't work on this flight, how do we fix it on the next flight? - Got it. - And then when you get
the NASA requirements for the next flight, make
sure we got everything in place to do what we
were supposed to do, so the data tapes come
from all around the world through Goddard Space
Flight Center's responsible for that, so they get us the
data and then we analyze it and determine what happened. Something would go wrong in the computer, and it always goes wrong
when something else is messing up the telemetry
system, so we would actually get what they call an octal dump. We have this 11 by 17 sheet of
paper, 10-bit octal numbers, so you'd have, there were four characters. Zero to seven's as high as
you go with octal arithmetic. So you got all these
things, I think it was like, maybe 40 columns and 30
rows or something like that, so we would get this thing printed out, and all it's just numbers, well,
the piece we're looking for is in a particular place down here. Well, the drop out is where we, you know, telemetry dropout, we would
actually get this printed out 11 by 7 fanfold paper,
spread it down this hallway, get down on your hands and knees, make a template, cut out
the, you'll have a number of measurements that'll
always be the same, you know, like a bolt, it never
changes, so we know what those number's oughta be. So we cut the holes out and slide it down page by page, "Oh, hey,
these all look good! "Okay, this frame's probably good." So we go find so many
columns, so many rows, find the number we want, write it down. - So you're looking for one --
- Go to the next one. - If it bungs up something
that you know is a fixed value then it probably bunged up something else. - That's right, and if
the fixed value's okay, then somewhere in there
our number's probably okay. - And then once you've
got the problematic one, I mean, is that just the
world's nastiest sudoku puzzle? How do you solve that? - Well, no, you may have,
you may have to do this for many, many, many frames. Then you take it to your desk
and take those octal numbers, convert 'em to decimal numbers, go to a calibration chart and say, "Okay, I got this number." Go up my chart and say that means it's five degrees Centigrade. So you write down five degrees, then you figure out what frame you are, and that's about what time it is, so you're, "At this time,
I had five degrees." Then you go to the next one. Now you do this for about two weeks, and finally you got enough
to plot a graph by hand. So you put all these numbers in and you plot it by hand, and then you say, "Hm, that wasn't the problem after all. "Oh, well, here we go again." (laughs) - [Linus] Oh, boy. - [Destin] This is Ed. Ed is the head curator. - Hi, Linus, how are you? This is kind of an in-the-hand
example of the memory cores that you can see woven
into the spread here and then kinda under the
magnification over here, and there's about eight
or nine of them in there. So like Luke was saying,
when you run the current through there, it starts
to spin that doughnut in a particular direction,
and that tells you whether it's the one or the zero. And you were saying they
were woven on by hand, and it was primarily
women that did the work, that had basically a bench top. - So they would have like
textile industry experience, I guess. - Um, I am actually not certain what their qualifications were, but they would sit with a bench top with this thing mounted in a holder with copper wire lengths and
tweezers and their fingers and a lot more patience than I have, to weave these things through there, to make sure they went
through appropriately, no kinks, no bends that
were out of the spec, and to actually make sure
that the little doughnuts go into across the way they should and that it was all uniform so everything would be
predictable behavior. - [Linus] Incredible. - [Destin] I just wanted you
to hold the physical bit, now you know what that's like. - I mean, this is, this
is more than 8 bits, so I'm holding at least a byte. (laughs) You can look at it that way. - [Destin] So when you look at this, what kind of emotion do you feel, when you look at this, Luke? Do you, do you, are you proud? - Is it fondness, or is it more just, "Thank goodness I don't have to work on that bloody thing any more"? - No, I'm gonna talk to one of my buddies when you go out the building, see if he'd hit you in the head. (laughs) - [Destin] To get this thing? - Yeah. No, that's a real piece of work, and it looks, to people that come in here, they say this just looks
so much like an antique. But again, we only had a few failures during the whole flight
that were intermittent. We never had a catastrophic failure. - People might say antique, but I would say hand-crafted. - Yes, it was a lot of
hand work went into these. - [Linus] Oh, you can
tell, I mean, even just, even these are clearly hand-baked. - Well, they got the goop on 'em because the big problem with
this thing is vibration. The memory that we were
looking at over there -- - Yeah, you got physical rings on there. - They test and test
and test on that thing to make sure that you
hadn't got a kink in a wire or a twist, 'cause if
you do, the vibration's gonna cause it to break. Those things were made by hand. The ladies actually wove these things like you're weaving a piece of cloth. Pretty amazing. - [Linus] Oh, this is fascinating. Thank you very much, by the way. - I wanna say thanks to the sponsor today, which is audible. I'm about to recommend a 13-hour audiobook about salt, and you're
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about the stuff I love. If you want to see more
of this interaction between Linus and Luke, it's incredible. Like on the second channel,
there's a 30 minute video of Luke going all the
way down the rabbit hole. This guy knows his stuff. Like, I feel like I know
rockets pretty well, Linus certainly knows computers, but when we're sitting
there, it's almost like Luke could just run around both of us. Go check that out on the second channel. Also go check out Linus's channel. Actually, I'll just let
Linus do an outro himself. Go check out Linus's
channel, Linus Tech Tips. He's talking about,
what's it called again? - The instrument unit,
basically we talk a little bit about the computer but
Destin's got a little more information on that, but I really love the cooling system on this thing, it's gonna blow your guys's mind. Unreal. - It's awesome, it's at
the top of the rocket because as you got all three
stages of the Saturn V, you need your instrument unit way up here so you can guide the Saturn V before the Apollo computer takes over, but Linus talks about details of power and how that stuff works. It's pretty cool. - Yeah. - [Destin] Thanks, dude, appreciate it. - See you guys. Thank you. - [Kids] You're welcome! - Thanks, guys! - [Destin] It's called space camp. - Space camp. - [Destin] Yeah, so all
those kids are here to learn how to be astronauts and fighter pilots. That's Luke. - [Linus] No! - [Destin] That's Luke. - No way! On the left there, apparently. - [Destin] That's pretty cool, huh? - [Linus] Luke Talley,
there it is, far left. That's nice. - [Destin] That's pretty neat, isn't it?
I was amazed when the engineer said they received the telemetry data as octal numbers printed on paper, and they had to parse this data manually, one octal word at a time.
Today you'd write a simple python script to do it. Holy moly!
Something they didn't mention in the video is that due to schedule constraints, IBM had to build the first few Instrument Units on the barge that carried them down the Mississippi River for delivery to Cape Canaveral. It was a long trip, so they had time. They made all the logistical arrangements to have components delivered to the barge at intervals along the river. When they were done with the assembly, they did the final testing on the barge too. By the time the barge made it to Kennedy Space Center, the Instrument Unit was ready to fly.
You can read about this and other amazing stories of how the creativity and perseverance of american industry built the Saturn V in NASA's official history of the Saturn rockets, Stages To Saturn by Roger E. Bilstein. Download it from NASA NTRS:
https://ntrs.nasa.gov/search.jsp?R=19970009949&hterms=sp-4206&qs=N%3D0%26Ntk%3DAll%26Ntt%3Dsp-4206%26Ntx%3Dmode%2520matchallpartial
Is it wrong that the first thing I thought when I saw Linus on the thumbnail was that he was going to drop the memory module?
Wow that's really amazing. I had no idea they made stuff like that by hand.
If you're not done nerding yet here's an almost but not quite the same thing: Scott Manley recently visited a team that woke up an Apollo computer!
The longer version of this (about 45 min) on Destin's second channel is totally worth the time if you found this interesting: https://youtu.be/6mMK6iSZsAs
Luke Talley shares lots of cool info on the coolant system for the computer and how the core program loop interacts with some of the other systems.
I love how Linus hardly gets to comment. The guy is like "I made the computer which steered the goddamn Saturn V. Who the fuck are you?"
Can't imagine how efficient your code had to be.
/u/MrPennywhistle makes awesome videos. I want to visit rocket city so bad.