Top secret! Titan nuclear missile guidance computer disassembled
Latest update time：2022-11-19
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I have been studying the guidance computer of the Titan II nuclear missile before, and I was lucky enough to get one recently.
Pictured below, this small computer was used in the 1970s to guide the Titan II nuclear missile to its target or put the Titan IIIC rocket into the correct orbit. The computer works with an inertial measurement unit (IMU), a system of gyroscopes and accelerometers that tracks the rocket's position and speed.
▲Multiple connectors on the top connect the computer to the IMU and the rest of the rocket
This computer is called "Magic 352". From the appearance, it is a black box with a size of 20×16×9 and weighs 80 pounds (about 36 kilograms). It is very surprising how such a heavy thing can be used in rockets. middle
Out of curiosity, I decided to take it apart and find out!
First, let's take a look at the internals. The computer can be divided into three parts: the front half houses the processor and core memory storage; there is no microprocessor in the computer, the processor is composed of hundreds of simple integrated circuits; the back half houses the interface motherboard, which is mainly used for Connect the rest of the analog circuit rocket; the middle part is relatively empty.
1. Digital part
The computer 's front cover is held in place by 18 screws, which when removed will reveal the computer's processor board and core memory.
As shown in the figure below, on the left are 7 circuit boards with TTL digital logic; in the middle are 2 core memory modules, each containing 8192 24-bit words, and there are 2 memory electronic boards next to the memory; on the right is the computer's switching power supply.
▲Showing circuit board, core memory module and power supply
The image below shows one of the digital logic boards, similar to the others. Each board has integrated circuits on both sides, so the backsides all look the same.
Each side of the board has space for 5 rows of 13 chips, allowing each board to hold up to 130 chips.
The PCB appears to have 6 layers, 2 wiring layers and 1 ground layer on each side. The connection between the two sides is made via 99 connections on the top of the board, rather than through holes.
The circuit board is covered with a
protective
coating to protect the circuitry. Even though this "antique" was decades old, the coating still gave off a strong smell of turpentine. The
edges of the board are metalized and slide tightly into the slot. Since there are no fans, a path is provided for heat dissipation.
These digital boards have a 198-pin connector on the bottom that plugs into a backplane, while the interface board has a smaller 128-pin connector.
▲Processor board PR1
These boards contain TTL chips, which may be MSI (medium-scale integration) chips such as counters, adders, or shift registers.
Note that this computer does not contain a microprocessor chip, but does have a processor built from simple building blocks (in the 1970s, microcomputers were often constructed from TTL chip boards).
Judging from the part numbers on the chips, they appear to be Signetics' CC2100 series products.
▲PCB traces can be seen on the chips, and the 7802 date code indicates that they were produced in the second week of 1978
An interesting feature of these boards, is that they lock to ensure that the board cannot be inserted into the wrong slot. This is keyed by splitting the hex nut in half. The circuit board and backplane connectors have matching halves, so the circuit board can only be plugged into the correct slot.
The picture below shows a portion of the backplane with the plate removed so we can see the connectors and half hex nuts. Note that each connector has a different angled hex nut for keying.
2. Core memory
The computer used magnetic core memory for storage (unlike the earlier Titan ASC-15 computer, which used rotating magnetic drums).
Starting in the 1950s, core memory was the primary form of computer storage until it was replaced by semiconductor memory chips in the 1970s. Core memory consists of thousands of thin ferrite rings called cores, each storing one bit. Magnetize the core clockwise or counterclockwise to store the value. The cores are arranged in a grid called a core plane, and applying power to specific row and column lines selects the specific core where the two lines cross.
The image below shows a close-up of the tiny magnetic cores in the Titan computer, and you can see that each core has 4 wires: vertical and horizontal red wires forming a grid to select the core wires. There are also 2 colored horizontal lines running through each core in the plane: the sense line (for reading) and the inhibit line (for writing). We can see on the right side these wires looping through the rows.
▲ Different 19-pin connectors connect the clock to the main control
In core memory, multiple planes are stacked together, one for each bit in a word. In most computers, the core planes are soldered together or soldered into a block, but the Titan computer's core memory is built using an unusual patented technology: the core and circuitry are mounted on a folded accordion-style long flex print on the circuit board.
This construction technique allows the core memory module to be opened like a book to access the core and circuitry.
▲The core module unfolds like a book
If you think of the core memory module as a book, each "page" is made of a metal plate with a flexible printed circuit board wrapped around both sides. There are 6 of these "pages", so there are 12 core memory planes, similar to the page below.
After careful counting, it was found that there were 128 horizontal lines and 128 vertical lines passing through the core plane, so there were 16,384 cores below.
128 vertical wires
are visible at the top and bottom
, running irregularly between the planes.
Note that these are thin wires that pass through the core and they continue uninterrupted across the entire core plane.
Gather the 128 horizontal core wires into bundles to extend between planes;
the left bundle proceeds downward and the right bundle proceeds upward.
▲One plane in core memory has 16384 cores
The complete module contains 24-bit words plus a parity bit, and the module contains 8192 words. The computer has 2 core modules so it can hold a total of 16K words.
▲Here 128 horizontal lines are connected to the circuit board
3. Core memory
Turn the computer over to reveal the circuit board behind the back panel. These interface boards are connected to connectors on the top of the computer as shown below. Through these interfaces, the computer receives velocity and attitude pulses from the inertial measurement unit (IMU). The computer sends analog control signals to various actuators and discrete (binary) signals to other parts of the rocket for thrusters, staging and other functions.
Also, on the left is the power supply. The power supply is connected to the power supply via a connector and cable on the top of the computer, which receives power from the rocket.
The interface board has various circuits, CTL, MUI and ADL boards are covered in TTL chips, similar to the boards in the digital part. However, the rest of the interface board is stuffed with analog components such as transistors, capacitors, resistors, diodes, hybrid modules, and a few TTL chips.
The VMX board below has 4 mysterious 6-pin black hybrid modules, and a ton of large capacitors. It's unclear what the board does, or why so many capacitors are needed...
▲
Like other boards, it is covered with a thick protective coating
4. Power supply
As shown below, this computer uses a switching power supply to efficiently convert the missile's power (probably 28V) into the voltage required by the computer. The power supply is very heavy, about 15 pounds. Since there are no fans, most of the weight is probably the metal needed to dissipate heat.
Internally, the power supply contains inductors and transformers, power transistors, and circuit boards. On the left side of the picture below is a bunch of filter capacitors in a large metal can. The inductors and transformers don't look like the inductors in commercial power supplies, but black squares.
As shown below, several circuit boards control the power supply, and they use metal can integrated circuits, unlike those found in commercial power supplies.
Since
the part numbers on these integrated circuits
do not provide
any useful information,
the guess
is that
they may be custom military parts.
The board is covered with a protective coating that not only protects it from moisture, but also gives the integrated circuit a golden sheen that's really nice to look at!
The power supply may generate 5V for the TTL chip, higher voltages to drive the core memory, and of course multiple voltages for the interface circuitry.
5. Summary
Aerospace computers are generally ignored in computer history, despite their use of many innovative technologies.
The Titan missile's computer, for example, used flexible PCBs for its core memory and surface mount integrated circuits years before they became common in commercial electronics. However, due to Moore's Law, the power of CMOS integrated circuits increased exponentially, so building computers with TTL chips became a technological
dead end
.
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