Greeting Earthlings. If you follow the channel, you know that I just finished building a driver
for an electromechanical Soyuz space clock. The clock belongs to famous investor and space
collector Steve Jurvetson. Steve had loaned us quite a few items: the space clock, a Titan
missile guidance computer, and a core memory module from the Saturn V guidance computer,
and it is high time we return them and tell him what we found about them.
Ken, Carl, Mike and I went together for this much anticipated visit.
[Steve] No way, is this mine? [Marc] Yeah! [Steve] Oh my God, check this out! You know,
whoever designed this back in the day, if they know that someone was going to revive,
it would make them very happy.
The ever enthusiastic Steve was ecstatic over my modest little box. I can hardly imagine
what he says when Elon shows him his latest rocket. We turned the clock on, with the expected
result that it soon drove the other office people crazy. But for us space nerds, we heard
nothing but music.
It was then Ken’s turn to bring back the Titan missile guidance computer. Ken did most
of the detective work on this one, and has written an in-depth article about his findings
which I’ll link in the description.
When it first came to us, it had never been opened, and was basically a big and very heavy
black lump of metal.
[Marc] It's very heavy you think they make it light but man. [Ken] Yeah, look at the
thickness of the the metal here. [Marc] It's super thick! And was it still sealed when
you got it? [Ken] Yeah, I vented out the nitrogen. Which is probably a good thing Steve mentioned
it, because otherwise there's like, you know, 500 pounds of force when I unscrew it. [Marc]
Ah, yeah, not good!
When Ken brought it to my lab, he had already opened it and removed most of the cards, but
had not yet succeeded to remove the core memory cards.
Here it is fully re-populated. Ken wrote a detailed article about it, which I will link
in the description. This computer was first used in the guidance system of the Titan III
satellite launch rockets, and later retrofitted in the Titan II missiles. The Titans were
powerful rockets, and Titan II is better known as the launch vehicles for the Gemini missions.
The Titan III launched the Viking probes to Mars and the two Voyager solar system exploration
probes in the 1980s.
The computer itself is a Magic 352, and was developed by Delco (a division of General
Motors) in the early 1970s. Ken just extracted one of the logic cards, which contain surface
mounted TTL chips, on 6 layer PCB boards. The computer has no microprocessor, and is
solely built out of medium integration scale TTL chips, very much like all mini-computers
were built in the 1970s.
The other side has the interesting looking analog interface boards, which come in all
sizes and shapes, mostly with transistors and mysterious circuits, including this hand-marked
module.
But the most intriguing part was probably the 16 kWord core memory module, which was
stubbornly stuck inside the computer. We soon discovered the key to its removal. It involved
voiding the warranty…
Uh, it says that you're going to void the warranty on this thing? [Ken] Yep, it says
"do not break seal", but Carl has discovered this hidden access panel so... [Marc] Which
would explain why we weren't able to take the memory stuff out. What is the date on
this computer? [Ken] So the parts are 78, 77, 79. [Marc] And look what we found underneath
this once we pried it off! It's just a seal plate, and then here are the real screws.
So no wonder we couldn't take the freaking module out!
All right, it went much better once we removed the hidden extra screws. They really did not
want this module to move during launch! Ooh, aah, looks promising.
We disassembled further, is that the the idea? [Ken] That's the idea, go for it! [Marc] All
right. Oh there's flex, there is flex circuitry in it. In 1978 my friends! Oh, I see the cores,
right here! Oh, plates of cores.
[Ken] We took out a whole pile of screws to remove these brackets, and now the core memory
opens like a book. Each board has a bunch of cores, and then the support logic, and
then there's just bare wires and flex connectors between them. [Marc] Yeah, there is 1978 flex
circuit, that's pretty impressive.
And you can read more about Ken’s further findings in the linked article.
Before we returned it, Ken made a nice plexiglass front window for it, so it could be displayed
properly, while we left the core memory proudly sitting on top.
Oh that's nice like this, it's really beautiful. [Steve] Isn't it a good display? [Marc] Such
an nice module!
Next we turned our attention to this holy piece of the Apollo Saturn V rocket that Steve
had loaned to us: I present to you the LVDC core memory module.
LVDC stands for Launch Vehicle Digital Computer. In many previous videos, we had talked about
the Apollo Guidance Computer, located in the command module and the LM. But there was another
independent guidance computer in the Apollo rocket of a completely different design. Let
me explain using another wonder of modern technology, the LEGO system.
So previously we talked a lot about the Apollo Guidance Computer, of which there are two:
one located in the Command Module, and the other one located in the LM, which during
launch is under the shroud here. But there was a third guidance computer for the Saturn
V launch vehicle, called the LVDC: Launch Vehicle Digital Computer. And it was located
in this black ring here, called the Instrument Unit, at the very top of the rocket.
And its function was to guide the rocket itself, the Saturn V. And of course it was all at
the top, because as you were staging down, you want to keep it with you. As the rocket
stages, which this incredible LEGO model does too, you keep it with you, right? You are
just with the S-IVB stage. You keep it until lunar insertion, and then after that
burn is completed the - let's see if I can do it without breaking things. Uh, that was
gone long time ago - the CSM separates, and then will come and pick up the LM, and
then they rely on the Apollo Guidance Computer. But all the ascent was relying on the LVDC,
with a possible backup: it could be taken over by the AGC, but actually that never happened
in the real flight.
And by the way, while we are talking about awesome LEGO models, that's their LM model.
And so I don't have the real thing like Steve Jurvetson, but I have the LEGO model - which
is almost the same. And look, the ascent stage separates! And they even have a brick for
the AGC, which is exactly where it should be. So at the back, you have a little AGC
brick. So the AGC was made out of LEGO, I'm sure you didn't know that.
But let’s go back to our Instrument Ring, which was a ginormous thing. You might wonder
what the technician is doing with his telescope in the corner. It’s not a telescope, but
most likely a laser, shining through a window on the side of the ring.
This was used to align the inertial platform or IMU prior to launch. You can see the ball
of the IMU on the other side of where he is shining his laser. There was a reference laser
on the ground shining all the way up to the window at the top of the rocket on the launchpad,
so the IMU was kept in alignment down to the last second before launch.
Not far from the IMU are two large rectangular boxes. In yellow, you finally see the LVDC,
the digital computer, and on top of it, in orange, its even larger companion the LVDA,
the Launch Vehicle Digital Adapter. That’s the box that had the IO and the Digital to
Analog circuits that interfaced the computer to the actual hardware on the rocket.
The last piece of the computer system was the FCC, the big black cylinder which I have
highlighted in the green box. FCC stands for Flight Control Computer. This so-called computer
was actually an analog computer.
It performed relatively simple signal processing, mostly analog computations and frequency filtering
of the error signals calculated by the digital computer, before they were applied to the
engine gimbal servos. This was difficult to do with the digital electronics of the time,
but mapped well to an analog computer based on operational amplifiers.
So very much like the AGC, the LVDC got its primary orientation information from the IMU,
interfaced to the engine gimbals, and was responsible for steering the rocket during
ascent. Unlike the AGC, it did not have an interface to the astronauts.
Made by IBM, it was at the opposite end of design philosophies from the AGC. Whereas
the MIT-designed AGC was all sheer brilliance and daring novelty, the IBM LVDC was the epitome
of conservative design.
Foremost, it was a triple redundant design, meaning every logic function was implemented
in triplicate, and a voting circuit would choose the answer given by the majority of
circuits. It was a 26 bit machine, but it used a serial design, meaning the ALU operated
on one bit at a time to greatly simplify the hardware, and therefore it was very slow - IBM
obviously prioritized reliability over performance.
And in that, it performed admirably, not skipping a beat when hit by lightning on Apollo 12’s
launch, correctly discarding the bad transient data and dutifully continuing to steer the
Saturn V to orbit.
But as conservative as its architecture was, its hardware implementation was far from stodgy.
It used IBM’s miniature hybrid circuits instead of ICs, and flat flex circuits for
interconnects.
These small metallic cans not ICs, these are ULDs. They are little hybrid on ceramic modules,
with individual diode and transistor dies, connected via traces and printed resistors.
IBM was wary of the newfangled ICs which they considered unproven and unreliable, and instead
made their miniature circuits out of individual parts, and relied on incredible micro-packaging
to achieve the required density.
Here you can see the inside of a ULD. The top of the ceramic, on the left, has a few
transistor and diode dies, and the underside on the right has the printed resistors.
The computer has the logic cards arrayed in the front, and the memory modules are plugged
at the back. Here is a period photo of the back of the unit, with one memory module plugged
in. And here is a picture of the unit with all of its 8 memory modules plugged in.
Each module had 8K half-words of core memory. The half words were 13 bits plus one parity
bit for added reliability. So this translates roughly to a 12 Kbyte module in modern terms,
for a max of 96 kBytes of computer memory.
On an assembled module, you can’t see the core ferrite stack, because it is covered
on all sides by driver boards. But here I have a picture of what the core stack actually
looks like in the middle.
Can you spin it around, because this is very three-dimensional, they have boards
on the top. [Steve] Exactly, I love that, like there's absolutely no homage to planar[ity],
you know, it has not fully sunk in yet.
[Ken] And so it's core memory, so you have your your tiny rings of core that you magnetize.
And so you have an X-Y grid to select which core you want. And so on the one side you
have your X - I think that this is the X drivers. [Steve] Okay. [Ken] So you have 128 wires
that go one way through the cores. And then on this side you have the Y drivers, you've
got 64 wires that go through the other way. So the Y board gives you 64 lines, which you
can see come along on the ribbon cable here. So they go through this way. And since you've
got 128 for the X, you need two boards. So that's why there's two boards here.
And then you can see a huge stack of hundreds of diodes in between. [Steve] Oh yeah, this
is actually amazing. Look at this manufacturing technique! [Ken] So the reason they have all
these diodes, is that for your 64 wires you don't want to have 64 driver circuits. [Steve]
Okay. [Ken] You can have like eight on one side and eight on the other side.
[Marc] This was a common trick used in core memory, where you would minimize the number
of drivers by grouping the wires in a multiplexed matrix arrangement, at the expense of necessitating
lots and lots of diodes. To save space for the many many diodes, they mounted them vertically
between two boards, in a configuration known as cordwood construction.
[Steve] So instead of like, a diode being on a circuit board, right, like you'd expect,
they're literally running perpendicular between the boards. Hundreds of them!
[Ken] So these chips are not integrated circuits, they're called ULD, Unit Logic Device. And
IBM didn't think integrated circuits were ready, so each one of these has like tiny
transistor and diode dies, discrete, mounted on ceramic and then thin film resistors.
[Marc] These colorful boards on the top and bottom are the sense amplifier boards, the
delicate amplifiers that read the faint signal from the cores, one for each bit in the word.
So there are 7 at the top and 7 at the bottom, for a total of 14 bits. Sense amplifiers are
still needed to this day in modern DRAM memory, but you never ever see them beautiful like this!
[Ken] So these amplify the signals coming out, then your 14 bit word goes to the computer,
which then converts it to serial, because the computer is running one bit at a time
in serial.
[Marc] And the reason we could not make it work and read it, is that some of the circuits
are broken or missing.
And you can see, this one is dislodged, this one is completely broken and completely missing,
this one is missing, and the damage is even worse on the other side. And you can see how
there is even more damage on this side. So here is a broken one, another broken one,
some dislodged ones. Unfortunately to get to the core memory itself - we could drive
it on our own - but as you can tell, it's all sealed and we couldn't remove the board
without removing the sealing. And it's just not worth touching this historical artifact
to read it. Because we would have only one eighth of the memory anyhow.
We even considered reverse engineering the broken circuits from a non broken one and rebuilding
an equivalent, but even then we would have only one chance at reading the module, because
reading core memory is destructive as I explained in my other video.
I should be able to read that one. I read this one. And I destroyed it, it's gone!
And since we don’t have another module to try it on first, it is very unlikely we’d
do it right the first time and then would risk losing the whole content. Finally, even
if we did that, we’d recover only 1/8th of the code. And to make matter worse, the
software is still ITAR classified, since it could be used to steer nefarious missiles,
so we would land in dangerous legal waters.
So we won't read it, but we can still admire it.
Okay, and this barely scratches the surface, this were only the first three items we returned.
There is much more to see, and then another crazy guest arrived, so I guess we will cover
that in the next episodes. See you then!
Whoa! I had a rapid [unscheduled] disassembly! Okay, it didn't work as i wanted to...