What do xenon lamps and the invention of radio have in common?
The box below is a 1960s German high voltage unit that CuriousMarc obtained
as part of an auction.
After some research, we determined that it is an Osram1 igniter2, which generates a 40-kilovolt pulse3
to ignite a xenon arc lamp.
The unit didn't work, so I opened it up, figured out its circuitry, and fixed it, so we could generate some sparks.
The circuit turned out to be very similar to a Tesla coil, although the sparks are much smaller.
The igniter, producing a nice 40 kV spark.
A xenon arc lamp generates light by producing a high-temperature plasma of ionized xenon between
two electrodes.
It produces bright white light that has a spectrum similar to daylight and is useful for movie projectors, searchlights, and laboratory uses.
Although the lamp is powered by a low-voltage, high-current DC power supply,
a high-voltage spark is required to start the arc, and that is the role of this 40 kV igniter.
Closeup of a 4 kW Osram xenon arc lamp for a movie theater. Image by Hyperlight, CC BY-SA 2.5.
I searched for information on this ignitor.
The only thing I found was a 1964 paper titled A Spectrofluorophosphorimeter
that described an experimental setup for measuring fluorescence and phosphorescence spectra.
The experiment used a 450-W Osram xenon arc lamp, ignited by a Z2201 igniter, the same as this one.
The research was done at SRI (Stanford Research Institute), just a few miles away, so there's a good chance that Marc obtained the exact unit that was used in this research.
The igniter's output is on a cone sticking out of the box. It also has five screw terminals for the 220V input, ballast, and ground. Photo courtesy of Marc Verdiell.
We opened up the unit and I examined the unusual components inside.
A large 220V to 7kV transformer is at the right of the photo below.
The output transformer is the reddish flat cylinder at the back left; this transformer's output is the connection pillar on the front of the unit.
In front of this transformer is a dark yellowish disk, a 1000pF 20kV capacitor.
The most unusual component is the ceramic cylinder in the front.
Inside the igniter, showing the transformers, capacitors, and spark gap.
I traced out the circuitry of the unit6.
It is a high-voltage circuit that is also sometimes used in Tesla coils (details).
The way it works is that the high voltage transformer raises the 220 V input to 7 kV.
This charges the high-voltage "tank" capacitor until it has enough voltage to break down the spark gap, causing a spark across it.
When the spark gap fires it conducts at low resistance. This creates a high-frequency resonant circuit between the tank capacitor and the output transformer's primary.
Energy is transferred to the secondary, at a much higher voltage, producing the 40 kV output.
As energy shifts back and forth between the primary and secondary, it is dissipated, until the spark gap stops conducting and the process repeats, thousands of
times a second.5
Schematic of a Tesla coil circuit. This is a less popular topology for a Tesla coil, but is the circuit used in the igniter. (The igniter has an output, not a torus, of course.) Schematic from Omegatron.
So where is the spark gap in this unit? It turns out to be the ceramic cylinder.
I opened up the cylinder and found a stack of eight metal disks with (maybe) carbon electrodes in the center. The disks are separated by mica washers to leave 0.33 mm gaps between each pair.
This forms a series of 7 tiny spark gaps.
The spark gap disassembled, showing the stack of contact disks and mica insulators inside the ceramic tube.
This type of spark gap is known as a "quenched spark gap".
Spark gap transmitters were the first form of radio transmitter, used from 1887 to 1920.
They used a spark to
transmit Morse code via radio waves (details).
The quenched spark gap was one type of spark gap used in these transmitters, as shown in the diagram below.
By combining multiple small gaps, the quenched spark gap could cool off efficiently.
We cautiously hooked the igniter to 220V to test it, but nothing happened.
I checked various parts of the circuit and everything seemed fine.
In the photo below, notice the pink block at the left that looks like a Lego piece.
This is a safety interlock that disconnects the 220 V input if the case is removed; the case has prongs that mesh with the interlock to close the circuit.
Eventually, we figured out that the safety interlock had some loose screws that weren't making contact.
This was tricky to find because when the case was open, the safety interlock was (of course) open.
Inside the igniter. The output transformer (reddish round unit) is at the top with the yellowish tank capacitor above it.
The ceramic spark gap is the cylinder in the middle. The pink Lego-link block is the safety interlock.
The HV power transformer is at the bottom (label visible).
T.
After tightening all the screws, the igniter worked.
Since we didn't have a xenon arc lamp, we used the unit to generate sparks instead.
Marc attached a strip of copper to the center output and a white wire to the ground,
bending them to form a small gap. He pulsed the power switch to produce brief sparks, as seen in the video below.
(Since the text on the unit indicates the unit should be powered for under 0.5 seconds,
we kept the sparks brief to prevent overheating.)
Although the repair was anticlimactic, at least we got some nice sparks.
Conclusion
Spark gaps generate radio waves across a wide spectrum;5 inventor David Hughes first noticed this interference in 1878. Marconi experimented with spark-gap transmitters
in the 1890s, discovering how to transmit telegraph signals across short distances and then between continents.
This work won Marconi the Nobel Prize for inventing radio.
The CuriousMarc video below explains in more detail how the spark gap generator led to radio.
Vacuum tubes made spark-gap transmitters obsolete by the 1920s, but these spark-gap circuits live on, igniting xenon arcs in modern headlights.
I announce my latest blog posts on Twitter, so follow me @kenshirriff for future articles. I also have an RSS feed.
Notes and references
You might know Osram as the maker of headlights4 and other lights.
The story starts with the Austrian chemist Carl Auer von Welsbach, who discovered four elements as well as inventing the gas mantle (used in Coleman lamps)
and the metal flint used in lighters.
He registered Osram as a trademark in 1906; the name was a combination of osmium and wolfram (tungsten), two elements he used in incandescent lamp filaments.
In 1919, the Osram company was formed in Germany. ↩
The front of the unit is shown below. Siemens-Schuckertweke AG is a German engineering company
that I think owned Osram at the time.
Under that are the warnings "Vorsicht! Hochspannung" (Danger! High voltage) and a circle labeled "In diesen Zone keine Metallteile" (No metal parts in this zone).
At the center of the circled zone is a pillar with a screw terminal; this is the connection for the 40 kV output.
At the bottom are connections for 220V / 50 Hz, which can be applied for a maximum of 0.5 s, as well as "zum Vorschaltgerät" (to the ballast).
Front view of the igniter. The black text is hard to read under the brown front.
The label on the back of the unit (below) says ZX 501, Höchstzulässiger Lampenstrom 25 A (Maximum lamp current 25 A),
Zündkreis (Ignition circuit) 220V/50Hz,
Zündsp. ca. 40 kV (Ignition voltage approximately 40 kV),
OSRAM - Best. - Nr. (Order number) Z2201.
"
The label on the back of the unit. Photo courtesy of Marc Verdiell.
Xenon headlights are also known as HID (high-intensity discharge) headlights.
These headlights produce most of their light from an arc through vaporized metal halides, such as scandium iodide.
However, it takes seconds to minutes for the light to heat up enough to vaporize these halides.
During this startup time, a xenon arc provides the headlight's illumination.
In other words, the xenon arc is just to provide light temporarily until the metal halides kick in.
HID headlights require an igniter/ballast circuit to provide the high voltage (25 kV) for ignition
and the regulated voltage (e.g. .41A, 85V) to power the light. These automotive circuits use modern switching power supply techniques and
are much smaller than our igniter. ↩
We measured the output from the igniter and found that it produces 2000-4000 very short spikes a second. The spikes decay very rapidly so they are about 1µs long, and are random noise in the tens of megahertz. This random noise has a very wide bandwidth showing that spark gap generators produce radio noise across a wide spectrum.
Oscilloscope trace pickingup electrical noise from the igniter over the air. Image from CuriousMarc's video.
I traced out the circuitry of the unit and made the rough schematic below.
The unlabeled rectangle is the ceramic spark gap cylinder.
The circuit is essentially the same as the Tesla coil schematic earlier, except there are two capacitors and an external ballast resistor
on the output side to limit current. (We did not use a ballast resistor, but shorted the two connections.)
I've been studying the guidance computer from a Titan II nuclear missile.
This compact computer was used in the 1970s
to guide a Titan II nuclear missile towards its target or send a Titan IIIC rocket into the proper orbit.
The computer worked in conjunction with an Inertial Measurement Unit (IMU), a system of gyroscopes and accelerometers
that tracked the rocket's position and velocity.1
The guidance computer, from Steve Jurvetson's collection.
Multiple connectors on top link the computer to the IMU and the rest of the rocket. The cover panels are protected by anti-tamper stickers so I probably voided the warranty by opening it.
(Click any photo for a larger image.)
This computer, called the Magic 352, is a
20"×16"×9" black box2 weighing 80 pounds, surprisingly heavy for something used in a rocket.4
Its sturdy aluminum case alone weighs 20 pounds.
Internally, the computer is divided into thirds. The front section holds the processor and the core memory storage.
There is no microprocessor in this computer; the processor is built from hundreds of simple integrated circuits.
The back section of the computer holds the interface boards, mostly analog circuitry to connect to the rest of the rocket.5
Unexpectedly, the middle section is mostly empty space.6
The computer was made by Delco, a division of General Motors3 that built a whole line of "Magic" aerospace computers.
The digital side
The computer's front cover is held on by 18 screws. Removing them reveals the computer's processor boards and core memory.
On the left are seven circuit boards with TTL digital logic.
In the middle are two core memory modules, each holding 8192 words of 24 bits. Two memory electronics boards are next to the memory.
At the right is the computer's switching power supply.
The front side of the computer, showing the circuit boards, core memory modules, and the power supply. The boards are identified with the code that is printed on each board.
The circuit boards have alphanumeric codes on them; PR1 through PR6 are probably processor boards 1 through 6.
It's unclear what "IOC" stands for; the IOC board looks like the other digital logic boards, but also has a circuit that's probably the
computer's clock. The "ME" and "CME" boards appear to have high-current driver circuitry for the core memory modules, so "ME" could be
"memory electronics".
Information on the Magic 352 computer is hard to obtain7 but
it uses 24-bit words (plus a parity bit), and it uses 2's complement fixed point.
It has 57 instructions (probably two per word) and can do an add/subtract in 6 microseconds.
The processor has six index registers.
The photo below shows one of the digital logic boards; the other digital boards are similar.
Each board has integrated circuits on both sides, so the back looks about the same.
(My photo album of all the boards is here.)
Each side of the board has space for 5 rows of 13 chips, for up to 130 chips per board.
The printed circuit board appears to have six layers; two wiring layers and a ground plane for the chips on each side.
Connections between the two sides are done through the 99 connections at the top of the board rather than vias.
The boards are covered with conformal coating to protect the circuitry; decades later, the coating still smells strongly of turpentine.
The edges of the boards are metalized and slide tightly into card guides, providing a path for heat to escape since there is no fan.
The digital boards have a 198-pin connector at the bottom that plugs into the backplane, while the interface boards (discussed later) have a smaller 128-pin connector.
Processor board PR1.
The boards are filled with TTL chips, probably MSI (medium-scale integration) chips such as counters, adders, or shift registers.
Note that this computer does not contain a microprocessor chip, but has a processor built from simple building blocks.
(In the 1970s, minicomputers were commonly built from boards of TTL chips.)
From the part numbers on the chips, they appear to be manufactured by Signetics, in a CC2100 series.
Unfortunately, even after extensive searching I couldn't find any documentation on these part numbers. (Please let me know if you have information on them.)
Some of the chips used by the computer. The PCB traces are visible in between the chips. The 7802 date code indicates they were manufactured the second week of 1978.
One interesting feature of the boards is they are keyed to ensure that a board can't be plugged into the wrong slot.
The keying is implemented by splitting a hex nut in half.
The circuit board and the backplane connector have matching halves, so the board can only be inserted into the right slot.
There are six ways to split a hex nut corner-to-corner, and two hex nuts (one on the top and one on the bottom), making
36 possible keying combinations. The photo below shows part of the backplane with the boards removed so the connectors
and half hex nuts are visible. Note that each connector has hex nuts at a different angle for the keying.
The half hex nuts fixed to the top and bottom of each connector are used to ensure each board is plugged into the right slot. Also note the cable of white and colored wires connecting the backplane to the external connectors on top of the computer. These slots are on the interface side of the computer.
This computer uses magnetic core memory for storage (in contrast to the earlier Titan ASC-15 computer, which used a rotating magnetic drum).
Core memory was the dominant form of computer storage from the 1950s until it was replaced by semiconductor memory chips in the 1970s.
Core memory was built from thousands of tiny ferrite rings called cores, with one bit stored in each core.
A core was magnetized either clockwise or counterclockwise to store a value.
Cores were arranged in a grid called a core plane; energizing a specific row wire and column wire selected the particular core where the two wires crossed.
The photo below shows a closeup of the tiny magnetic cores in the Titan computer.
There are four wires through each core: the vertical and horizontal red wires form the grid to select a core.
Two colorful horizontal wires pass through each core in the plane: the sense line (used for reading) and the inhibit line
(used for writing). You can see these wires looping from row to row at the right.
Closeup of the cores in a core plane. The cores appear glossy because they are covered in conformal coating.
In a core memory, multiple planes are stacked together, one plane for each bit in a word.
In most computers, the core planes were welded or soldered together into a block, but the Titan computer's core memory
was built with an unusual patented technique:
the cores and the circuitry were mounted on a long flexible printed circuit board that was folded accordion-style.
This construction technique allows a core memory module to be opened like a book to access the cores and circuitry.
The core module unfolds like a book. The circuitry and core planes are on a flexible printed circuit board that is folded accordion-style and wrapped around metal carriers.
If you view the core memory module as a book, each "page" is constructed from a metal plate with the flexible printed circuit board wrapped over both sides.
There are 6 of these "pages", so there are 12 core memory planes similar to the one below.
Careful counting shows there are 128 horizontal wires and 128 vertical wires through the core plane, so there are 16,384 cores below.
The 128 vertical wires are visible at the top and bottom, running loosely from plane to plane.
Note that these are the delicate wires through the cores, passing continuously and unprotected through the entire set of core planes.
The 128 horizontal core wires are gathered into bundles to run from plane to plane; the left bundle proceeds downward, and the right
bundle proceeds upward.
One plane in the core memory has 16,384 cores. It consists of eight smaller regions ("mats"); each mat has 32×64 cores.
To the right of the cores (above) is the circuitry to handle that plane.
This circuitry includes sense amplifiers to read the signals from the core plane, and inhibit drivers for writing data to the plane.
These integrated circuits are mounted on the same flexible PCB as the core planes.
The flexible printed circuit board is attached to standard rigid printed circuit boards at both ends; these boards form the outside of the module.
The end boards also have connectors that plug into the backplane, providing the connection between the core modules and the computer.
The photo below shows one of the end boards.
Note that this board has just half the cores of a normal board.9
The reason is that this board holds the parity bit, while the other 12 planes each hold two bits.
Thus, the complete module holds words of 24 bits plus one parity bit, with 8192 words in the module.
The computer has two core modules, so it holds a total of 16K words.10
This board at the end of the core module has half of the regular core plane. Note the numerous connections to the left of the core; the 128 horizontal wires are connected to the circuit board here. The packages at the far left each hold 8 diodes.
The interface circuitry
Turning the computer around reveals the circuit boards behind the back panel.
These interface boards are wired to the connectors on top of the computer.
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, as well as discrete (binary) signals to other parts of the rocket for
thrusters, staging, and other functions.
On the left is the power supply. The power supply receives power from the rocket through the connector on top of the computer and the cable to the power supply.
Cards in the back of the computer provide interfaces between the computer and external components. Each card has a three-letter code on it, but the meanings are unknown. The cables between the backplane and the connectors on top of the computer are behind the indicated supports.
In contrast to the digital boards, which all appear similar, the interface boards have a wide variety of circuits.
The CTL, MUI, and ADL boards are covered in TTL chips, similar to the boards in the digital section.
The rest of the interface boards, however, are crammed with analog components such as transistors, capacitors, resistors,
diodes, and hybrid modules, along with a few TTL chips.
The interface boards have the analog components on the front only (probably because there isn't enough clearance on the back) and usually a few TTL integrated circuits on the back.
I traced out some of the circuitry on the "AGO" board below and found 18 current-controlled outputs connected to TTL interface chips in the middle
of the board.
This board probably provides binary "discrete" outputs.
The AGO interface board; the "AGO" label is at the top left.
Note the different keying on the half-nuts on either side of the connector.
The VMX board below has four mysterious 6-pin black hybrid modules along with numerous large capacitors.
It's unclear what function this board has, or why it needs so many capacitors.
The VMX interface board. Like the other boards, it is covered with a thick conformal coating. The connector at the bottom is much narrower than the connectors on the digital boards.
The CON board uses hybrid modules including a large red
"Angstrohm" module that has hand-lettered labeling on it.
The "Angstrohm" module has 11 numbered pins, 3 "Z" pins, and a "BAE" pin.
Power supply
The computer uses a switching power supply to efficiently convert the missile's power (probably 28 volts) to the voltages required
by the computer.
The power supply is surprisingly heavy, about 15 pounds.
Much of the weight is probably metal needed to dissipate heat since there is no fan.
The switching power supply used by the computer. The two cable connectors provide power to the digital and interface sides of the computer. The power supply receives electricity through the connector on the front.
Inside, the power supply is packed with inductors and transformers, power transistors, and circuit boards.
A stack of filter capacitors in large metal cans is visible at the left in the photo below.
The inductors and transformers don't look like the inductors in commercial power supplies, but are black blocks.
The switching power supply used by the computer.
Several circuit boards control the power supply. They use metal-can integrated circuits, unlike the integrated circuits in commercial power
supplies. The part numbers on these integrated circuits didn't turn up anything useful so they may be custom military parts.
The boards are covered with a conformal coating to protect them against humidity and other threats. The conformal coating gives a
shiny golden color to the integrated circuits.
Closeup of a board in the power supply.
The power supply probably generates 5 volts for the TTL chips, along with a higher voltage to drive the core memory, and multiple
voltages for the interface circuits.
History and background
In this section, I summarize the complex history of the Titan missile and rocket, and its various guidance computers.
The Titan missile, deployed from 1959 to 1987 was the largest ICBM deployed by the United States and delivered a
9 megaton nuclear bomb.
To get a sense of how large the Titan was, the currently-deployed Minuteman missile weighs a third as much and its warhead has 1/25 the yield.
For much of its life, the Titan II's guidance computer was
the IBM ASC-15 (Advance System Controller), dating to 1962.
This was a 27-bit serial, transistor-based computer using discrete components in welded encapsulated modules.
For storage, it used a rotating magnetic drum that held 3,840 words.
This computer was used on the Titan II and Titan III, as well as the early Saturn I flights.11
Around 1964, the Titan II missile was modified for use as a satellite launcher called the Titan III.
The most visible change was the addition of two solid rocket boosters for many Titan III launches.
The first Titan III flights continued to use the ASC-15 guidance computer, but the project
switched to the Univac 1824M Digital Flight Control System.
This computer was more powerful and able to handle flight control as well as guidance and navigation.
It first flew on Titan IIIC on Feb 9, 1969.
However, the Univac 1824
project ended in 1969 due to cost and schedule over-runs.
Titan IIIC launch with an unmanned Gemini capsule, as part of the MOL project (1966). Photo from NASA.
Meanwhile, the AC Spark Plug division of General Motors developed the Magic family of computers for airborne guidance starting in 1962;
I wrote a detailed article on the Magic computers.
Delco used some of these computers in an inertial measurement unit (IMU) guidance system called the
Delco Carousel.12
The Carousel IV
was a popular navigation system, used on commercial planes including the 747, 707, and DC-8.
The Carousel IV used the Magic 311 computer (1967) and then the Magic 351 computer (1970).
The Carousel IV navigation system (with the Magic 351 computer) was turned into a military navigation system called the Carousel V, using the Magic 352 missile guidance computer (MGC).
(This is the computer I examined in this blog post.)
For space use, this system became the Universal Space Guidance System (USGS).
The Titan IIIC rocket switched from the Univac computer to the USGS, first flying with it on December 13, 1973
(details).
After its use on the Titan III, the USGS system was retrofitted onto the Titan II missile, replacing the obsolete ASC-15
(details) in a project called RIVET HAWK (1975-1976).
To summarize, the Titan program used several different computers as techology advanced, ending up with the computer I examined in the 1970s.
Conclusion
Aerospace computers are mostly ignored in computer histories, even though they used a lot of innovative technologies.
This Titan missile, for instance, computer used flexible PCBs in its core memories.
It also had surface-mounted integrated circuits, years before they were common in commercial electronics.
Building computers out of TTL chips became a technological dead end, however, as the capabilities of CMOS integrated circuits increased
exponentially, following Moore's law.
You can see photos of the full set of boards here; the interface boards are worth examining due to
their varied circuitry.
I announce my latest blog posts on Twitter, so follow me @kenshirriff for future articles. I also have an RSS feed.
Thanks to
Steve Jurvetson.
for supplying the computer.
Notes and references
Guidance systems use a variety of algorithms, with earlier low-power computers using simple guidance algorithms, while
later computers used more complex algorithms that provided increased accuracy and flexibility.
The Titan II used "delta" guidance, a simple guidance algorithm for low-power computers.
In this guidance system, the algorithm attempts to keep the missile on a pre-computed path, using a third-order polynomial to
steer back to the correct path.
The Titan IIIC required complex guidance software since the flight went through multiple stages.
A typical Titan IIIC mission put a satellite into a geosynchronous orbit at an altitude of 19,323 nautical miles.
To do this, the rocket launched and ascended to a parking orbit between 80 and 235 nautical miles,
using Stage 0 (the boosters), Stage 1, and Stage 2.
The rocket then used Stage 3 to move to an elliptical transfer orbit with an apogee of 19,323 nautical miles.
Another rocket burn put the vehicle into a circular orbit at this altitude. Finally, the payload separated from the rocket, putting the satellite into geosynchronous orbit.
The point is that the guidance computer needed to perform many different guidance tasks, as well as controlling the various rocket stages.
The overall Titan IIIC guidance algorithm is called "explicit" guidance, where an explicit solution is computed during flight to reach the desired
end result.
(I haven't been able to determine if the Titan II switched to this guidance algorithm when the computer was upgraded.)
For more information on the physical characteristics of the Magic 352 computer, see Space Tug Equipment Data Bank page 58. ↩
It's difficult to sort out the permutations of Delco, AC Spark Plug, AC Electronics, AC Delco, and so forth.
AC Spark Plug started in 1908 and became a division of General Motors in 1927. It was named after Albert Champion who also started Champion spark plugs.
AC Spark Plug's Milwaukee manufacturing facility became AC Electronics in 1965, with a focus on inertial navigation (details).
Meanwhile, Dayton Engineering Laboratories (Delco) was founded in 1909, and acquired by General Motors in 1918.
GM's defense systems laboratory was started in 1962 and merged into Delco Systems Operations in Goleta (where this Titan guidance computer was built).
In 1970, the Delco Radio Division and AC Electronics Division of General Motors Corporation were
consolidated into a new Delco Electronics Division.
In 1985, GM purchased Hughes Aircraft and merged it with Delco to form Hughes Electronics, which was sold to Raytheon in 1997. ↩
The photo below shows the label on the computer, serial number 69.
The "CP-1331/DJW" designation is a military component designator.
The "CP" indicates a computer unit and 1331 is the model number.
The "DJW" is an "AN System" military designation for a guidance system, specifically "Missile/Drone Electromechanical Flight Control Equipment".
The label from the Titan missile guidance computer.
The computer also has a repair label showing it was last repaired on March 14, 1986.
The repair label on the computer.
Each removable panel was protected with tamper-proof seals:
The sticker says "DO NOT BREAK SEAL". I broke the seals.
The computer also had an attached service tag. The penalty for removing the tag is up to a year in prison, so it's worse than a mattress tag.
At the back left of the computer is a fill valve, used to pressurize the computer with nitrogen to 5 PSI above ambient.
The valve appears to be a Schrader valve, the same as on an automobile tire.
Before opening the computer, I vented the nitrogen and found that the computer was still pressurized decades later. ↩
The underside of the computer has an access panel for the cables in the central section.
The photo below shows the view looking up through this access panel, showing the connectors on top of the computer, as well as
the cables attached to them.
This part of the computer is almost entirely empty space.
The backplane for the interface side of the computer is visible in the bottom of the photo; the boards plug into the other
side.
View into the central part of the computer showing the cabling.
Most of the connectors on top of the computer are 61-pin circular MIL-Spec connectors. Note the keying pins sticking out of the circular shell below. Each connector has different keying to prevent attaching a cable to the wrong connector.
The power input uses a 31-pin connector with larger pins that support higher current.
One of the connectors on the computer, labeled "J5".
Most of the connectors currently have yellow plastic caps, while two have metal screw caps.
I think that the metal caps are for test connectors that would remain covered in flight, while the plastic caps are temporary
covers for connectors that would be cabled up in flight. The test connectors are wired to the digital side of the computer. ↩
The wiring topology of the core memory module is worth noting.
Because the parity end board has half of a regular core plane, it has 64 Y wires instead of 128. These 64 wires pass through the cores and then
do a U-turn, returning to the next plane as the other half of the 128 wires.
The 128 X wires, on the other hand, pass through the cores and then are terminated on the board.
The board at the other end terminates the 128 Y wires (as two logical groups of 64) and the other end of the 128 X wires.
Both boards have numerous diode packages for these wires. ↩
I calculated that the computer's two core memory modules hold a total of 16K words of 24 bits plus parity.
This matches the Magic 352 memory size specified in
this article.
However, another document says the Titan IIIC computer has
16K of memory with 2K erasable (it's unclear if these numbers are bytes or words).
There's a patent related to the Titan computer describing a core memory that combines
DRO (destructive read out, i.e. RAM) and NDRO (non-destructive read out, i.e. ROM).
The ROM is implemented by omitting cores to store 0 bits.
I believe the ROM was an optional feature, so you could get 14K of ROM and 2K of RAM, for instance. ↩
The Gemini space flights (1964-1966) used a Titan II GLV missile,
but the guidance system was entirely different.
Gemini removed the Titan II inertial guidance and replaced it with a General Electric Mod IIIG radio guidance system, for guidance from the ground (details).
The Gemini capsule contained the Gemini Guidance Computer (OBC), built by IBM. ↩
The Carousel IMU got its name because the inertial platform rotated at 1 RPM (like a carousel) to reduce drift errors
(details).
Here is a photo of a commercial Delco Carousel.
The Titan computer was connected to an IMU that was probably similar inside, but packaged in a black box that resembled the computer but more cubical. ↩
This blog post examines a 1980s chip used in a Soyuz space clock.
The microscope photo below shows the tiny silicon die inside the package, with
a nice, geometric layout.
The silicon appears pinkish or purplish in this photo, while the metal wiring layer on top is white.
Around the edge of the chip, the bond wires (black) connect pads on the chip to the chip's pins.
The tiny structures on the chip are resistors and transistors.
Die photo of the Soviet 134ЛА8 (134LA8) NAND gate integrated circuit. (Click any photo for a larger image.)
The chip is used in the clock shown below.
We recently obtained this digital clock that flew on a Soyuz space mission.1
The clock displays the time on the upper LED digits and provides a stopwatch on the lower LEDs.
Its alarm feature activates an external circuit at a preset time.
I expected that this clock would have a single clock chip inside, but
the clock is surprisingly complicated, with over 100 integrated circuits on ten circuit boards.
(See my previous blog post for more information about the clock.)
Space clock from Soyuz with the cover removed.
The clock's circuit boards can be opened like a book to reveal the integrated circuits and other components, thanks to the flexible wiring harnesses that connect the boards.
The integrated circuits are mostly 14-pin "flat packs" in metal packages, surface-mounted on the printed circuit boards.
I wanted to know more about these integrated circuits, so I opened one up,2 took photos, and reverse-engineered the chip's circuitry.
The wiring bundles are arranged so the boards can swing apart. The quartz crystal that controls the clock's timing is visible in the upper center. The clock's power supply is on the boards at the right, with multiple round inductors.
Soviet integrated circuits
The clock is built from TTL integrated circuits, a type of digital logic that was popular
in the 1970s through the 1990s because it was reliable, inexpensive, and easy to use.
(If you've done hobbyist digital electronics, you probably know the 7400-series of TTL chips.)
A basic TTL chip contained just a few logic gates, such as 4 NAND gates or 6 inverters, while
a more complex TTL chip implemented a functional unit such as a 4-bit counter.
Eventually, TTL lost out to CMOS chips (the chips in modern computers), which use much less power and are much
denser.
The photo below shows a chip with its metal lid removed.
The tiny silicon die is visible in the middle, with bond wires connecting the die to the pins.
This integrated circuit is very small; the ceramic package is 9.5mm×6.5mm, considerably smaller than a fingernail.
To open up a chip like this, I normally put it in a vise and then tap the seam with a chisel.
However, in this case, the chip decapped itself—while I was looking for a hammer, the top suddenly popped off due to the pressure
from the vise.
The integrated circuit with its metal lid removed, showing the tiny silicon die inside.
The chip I'm examining has the Cyrillic part number 134ЛА8 (134LA8)6.
It implements four open-collector NAND gates, as shown below.4
The NAND gate is a standard logic gate, outputting a 0 if both inputs are 1, and otherwise outputting a 1.
An open-collector output is slightly different from a standard output.
It will pull the output pin low for a 0, but for a 1 it just leaves the output floating ("high impedance").5
An external pull-up resistor is required to pull the output high for a 1.
The clock uses three of these chips: one in the quartz crystal oscillator circuit, and another functioning as inverters in another part of the clock.3
Logic diagram of the Soviet 134ЛА8 (134LA8) integrated circuit, with pin numbers.
The Soviet Union lagged about 9 years behind the US in integrated circuit development.7
The lag would have been much larger, except the Soviet Union copied many Western integrated circuits.
As a result, most of the Soviet TTL chips have Western equivalents.4
However, the 134ЛА8 chip that I examined is different from Western chips8
with two unusual features.
First, to reduce the number of external resistors, this chip includes two pull-up resistors on the chip that can be wired up as desired.
Second, the chip shares two NAND gate inputs, which frees up the two pins used by the resistors.
Thus, even though the Soviet Union was copying integrated circuits, they were also creatively designing their own chips.
Integrated circuit components
Under the microscope, the transistors and resistors of the integrated circuit are visible.
The silicon die appears in shades of pink, purple, and green, depending on how different regions of the chip have been "doped".
By doping the silicon with impurities, the silicon takes on different semiconductor properties, making N-type and P-type silicon.
On top of the silicon, the white lines are metal traces that wire together the components on the silicon layer.
The photo below shows how a resistor appears on the silicon die.
A resistor is formed by doping silicon to form a high-resistance path, the reddish line below. The longer the path, the higher the resistance, so
the resistors typically zig-zag back and forth to create the desired resistance.
The resistor is connected to the metal layer at both ends,
while another metal passes over the resistor shown below.
A resistor on the integrated circuit die.
This chip, like other TTL chips, uses bipolar NPN transistors.
These transistors have N-type silicon for the emitter, P-type silicon for the base, and N-type silicon
for the collector. On the IC, the transistors are constructed by doping the silicon to form layers with different properties.
At the bottom of the stack, the collector forms the bulk of the transistor, doped to form N-type silicon (the large green area below).
On top of the collector, a thin region of P-type silicon forms the base; this is the reddish region in the middle.
Finally, a small square N-type emitter is formed on top of the base.
These layers form the N-P-N structure of the transistor.
Note that the metal wiring to the collector and base is off to the side, away from the main body of the transistor.
An input transistor on the integrated circuit die. The transistor is surrounded by an isolation ring (dark color) to separate it from the other transistors.
TTL circuits typically used transistors with multiple emitters, one for each input, and this can be seen above.
A multiple-emitter transistor may seem strange, but it is straightforward to build one on an integrated circuit.
The transistor above has two emitters wired up.
Close examination shows there are four emitters, but the two lower unused emitters are shorted to the base.
The output transistors on the chip produce the external signal from the chip, so they must support much higher current than the
other transistors.
As a result, they are much larger than the other transistors.
As before, the transistor has a large N-type collector region (green), with a base on top (pink), and then emitter on top of the base.
The output transistor has long contacts between the metal layer and the silicon, rather than the small square contacts of the previous transistor.
The emitter (wired in a "U" shape) is also much larger.
These changes allow more current to flow through the transistor.
In the photo below, the transistor on the left has no metal layer, so its silicon features are more visible.9
The transistor on the right shows the metal wiring.
Two output transistors on the integrated circuit die. The one on the left is unused, while the one on the right is wired into the circuit by the metal layer.
How a TTL NAND gate works
The schematic below shows one of the open-collector NAND gates in the chip.
In this paragraph, I'll give a brief explanation of the circuit; you can skip this if you want.10
To understand the circuit, first assume that an input is 0.
The current through resistor R1 and the base of transistor Q1 will flow out through the transistor's emitter and the low input.
Transistor Q2 will be off, so R3 pulls Q3's base low, turning Q3 off.
Thus, the output will float (i.e. open-collector 1 output).
On the other hand, suppose both inputs are 1.
Now the current through R1 can't pass through an input so it will flow out the collector of Q1 (i.e. backward) and into Q2's base, turning on Q2.
Q2 will pull Q3's base high, turning on Q3 and pulling the
output low.
Thus, the circuit implements a NAND gate, outputting 0 if both inputs are high.
Note that Q1 isn't acting like a normal transistor, but instead is "current-steering", directing the current from R1 in one direction or the other.
Schematic of one gate in the integrated circuit. This is an open-collector TTL NAND gate.
The diagram below shows the components for one of the NAND gates, labeled to match the schematic.
(The three other NAND gates on the chip are similar.)
The wiring of the gate is simple compared to most integrated circuits; you can follow the metal traces (white) and match up the wiring with the schematic.
Note the winding path from the ground pad to Q3.
Q1 is a two-emitter transistor while Q3 is a large output transistor. Two unused transistors are below Q2.
The die, showing the components in a gate. Components are labeled (blue) for one of the NAND gates, while pins are labeled in red. The pull-up resistors are above and below the Vcc wire.
Conclusion
This Soviet chip from 1984 is simple enough that the circuitry can be easily traced out,
illustrating how a TTL NAND gate is constructed.
The downside of simple chips, however, is that the Soyuz clock required over 100 chips to implement basic clock functionality.
Even at the time, single chips implemented wristwatches and alarm clocks.
Now, modern chips can contain billions of transistors, providing an extraordinary amount of functionality, but
making the chip impossible to understand visually.
My previous blog post discussed the clock's circuitry in detail and
I plan to write more about the clock,
so follow me @kenshirriff (or on RSS) for details.
Until then, you can watch CuriousMarc's video showing the disassembly of the space clock:
Notes and References
CuriousMarc obtained the clock from an auction and it
was advertised as flown to space, but we don't know which mission it was flown on.
The date codes on the components inside the clock are mostly from 1983, with one from 1984, so the clock was probably manufactured in 1984.
The Russian name for the clock is "Бортовые Часы Космические" (Onboard Space Clock), which is abbreviated as "БЧК". ↩
Don't worry; I didn't destroy any of the chips in the clock. We bought duplicate chips on eBay for reverse-engineering.
I was surprised that most of these 1980s-era chips are not too hard to obtain. ↩
I don't see any obvious reason why the 134ЛА8 chip was used instead of an inverter chip.
Surprisingly, even though the 7404 hex inverter chip was extremely common in US designs, the clock doesn't use any inverter chips at all. ↩
For more information on Russian integrated circuits, including the ones used in the clock, see the databook Интегральные микросхемы и их зарубежные аналоги (Integrated circuits and their foreign counterparts).
(The title makes it explicit that they were copying foreign chips.)
Be warned that the databook's description of the 134ЛА8 has a few typos. ↩↩
One reason to use open-collector gates is to get an AND gate "for free".
Connecting outputs together produces a wired-AND;
if any output is a 0, the tied-together output is a 0.
(Tying together NAND gates is equivalent to AND-OR-INVERT logic.)
Open-collector outputs can also be used on a bus, where multiple devices or boards can write signals to a bus line (as in the Xerox Alto)
without electrical conflict.
This use is obsolete, though; tri-state outputs provide much better performance. ↩
One nice thing about Russian ICs is that the part numbers are assigned according to a
rational system,
unlike the essentially random numbering of American integrated circuits.
Two letters in the part number indicate the function of the chip, such as a logic gate, counter, flip flop, or decoder.
For example, consider the label "Δ134 ЛA8A".
The series number, 134, indicates the chip is a low-power TTL chip.
The "Л" (L) indicates a logic chip (Логические), with "A" indicating the NAND gate subcategory.
Finally, "8" indicates a specific type of NAND chip in the ЛA category.
As with American chips, the "0684" date code on the chip indicates that it was made in the 6th week of 1984. ↩
Two CIA reports (1974 and 1986) provide information on the lag between Soviet IC technology and Western technology.
"Microcomputing in the Soviet Union and Eastern Europe", ABACUS, 1985, discusses how the Soviet Union copied American microprocessors,
especially Intel ones. ↩
The 7400 series includes several quad open-collector NAND gate chips, such as the 7401, 7403, 7426, 7438, and 7439.
These are all different from the Soviet chip.
A die photo of the 74S01 is here; I think the Soviet chip has a much
nicer layout. ↩
The integrated circuit has a few unused transistors. In addition, the input transistors have 4 emitters, but only two of them are used.
This is probably so the same silicon die can be used to manufacture multiple integrated circuits by changing the metal layer.
For instance, the 4-emitter transistors could be used for 3- or 4-input NAND gates. Alternatively, the unused transistors could be used to
create a hex inverter chip. ↩
For a detailed explanation of how TTL gates work, see this page. ↩
We recently obtained a clock that flew on a Soyuz space mission.1
The clock, manufactured in 1984, is much more complex inside than you'd expect, with over 100 integrated circuits on ten circuit boards.
In this blog post, I examine the clock's circuitry and find that it needed so many chips because it was implemented with simple TTL logic.
The clock also provides a glimpse into the little-known world of Soviet aerospace electronics and how it compares to American technology.
"Onboard space clock" from a Soyuz mission. The clock provides the time, an alarm, and a stopwatch.
The Soyuz series of spacecraft was designed for the Soviet space program as part of the race to the Moon.
Soyuz first flew in 1966 and has made more than 140 flights over the past 50 years.
The spacecraft (below) consists of three parts.
The round section on the left is the orbital or habitation module, holding cargo, equipment, and living space.
The descent module in the middle is the only part that returns to Earth; the astronauts are seated in the descent module during
launch and reentry.
Finally, the service module on the right has the main engine, solar panels, and other systems.
Soyuz TMA-7 spacecraft departing from the International Space Station, 2006. Photo from NASA.
The descent module contains the spacecraft's control panel (below).2 Note the digital clock in the upper left.
Early Soyuz spacecraft used an analog clock, but from 1996 to 2002, the spacecraft used a digital clock.3
The digital clock was also used in the Mir space station.
The clock was eliminated from later Soyuz spacecraft, which used two computer screens on the control panel in place of the earlier controls.
Control panel from a Soyuz spacecraft. The digital clock is in the upper left of the panel. The screen in the middle is a TV monitor. Photo from Stanislav Kozlovskiy, CC BY-SA 4.0.
A closer look at the clock
The diagram below shows the clock's labels translated into English.
The clock has three functions: the time, an alarm, and a stopwatch.
The "Clock of Current Time"5 mode shows the current Moscow time on the six upper LED digits, while "Announcement" shows the alarm time.
The alarm can be set to a particular time; at that time, the clock triggers a relay activating an external circuit in the spacecraft.4
The clock is set using the "Correction" mode; digits are incremented using the "Enter" button.
The lower half of the unit is the stopwatch;
the bottom four LEDs display elapsed minutes and seconds.
The lower pushbutton stops, starts, or resets the stopwatch.6
Finally, the power switch at the right turns the clock on.
Front of the clock. The red text is the translation of the Russian labels into English.
We wanted to see what was inside the clock, of course, so
Marc unscrewed the cover and removed it from the clock.
This revealed a dense stack of circuit boards inside.
The clock was much more complex than I expected, with ten circuit boards crammed full of surface-mount ICs and other components.
The components are mounted on two-layer printed-circuit boards, a common construction technique.
The boards use a mixture of through-hole components and surface-mount components.
That is, components such as resistors and capacitors were mounted by inserting their leads through holes in the boards.
The surface-mount integrated circuits, on the other hand, were soldered to pads on top of the board.
This is more advanced than 1984-era American consumer electronics, which typically used larger through-hole integrated circuits and didn't
move to surface-mount ICs until the late 1980s. (American aerospace computers, in contrast, had used surface-mount ICs since the 1960s.)
Space clock from Soyuz with the cover removed.
One interesting feature of the clock is that the boards are connected by individual wires that are bundled into wiring harnesses (below).
(I expected the boards to plug into a backplane, or be connected by ribbon cables.)
The boards have rows of pins along the sides, with wires soldered to these pins.
These wires were gathered into bundles, wrapped in plastic, and then carefully laced into wiring harnesses that were tied to the boards.
The clock has point-to-point wires, wrapped into neat harnesses.
At first, we thought that further disassembly of the clock would be impossible without unsoldering all the wires, but then we realized that the wiring harnesses were
designed so the boards could be opened like a book (see below).
This allowed us to examine the boards more closely.
Inconveniently, some pairs of boards were soldered together at the front by short wires, so we couldn't see both sides of these boards.
The wiring bundles are arranged so the boards can swing apart.
In the photo above, you can see the numerous integrated circuits in the clock.
These are mostly 14-pin "flat pack" integrated circuits in metal packages, unlike contemporary American integrated circuits which were usually packaged in black epoxy.
There are also some 16-pin integrated circuits, encased in pink ceramic.
The circuitry inside
The next step was to examine the circuitry in more detail, which I'll discuss starting at the back of the clock.
A 19-pin connector7 linked the clock to the rest of the spacecraft.
The spacecraft provided the clock with 28 volts through this connector, as well as external timing pulses and stopwatch control signals.
The clock could signal the spacecraft through relay contacts when the alarm time was reached.
This 19-pin connector interfaces the clock to the spacecraft.
The two circuit boards at the back of the clock are the power supply, which was more complex than I expected.
The first board (below) is a switching power supply that converts the spacecraft's 28-volt power to
the 5 volts required by the integrated circuits.
The round ceramic components are inductors, ranging from simple coils to complex 16-pin inductors.
The control circuitry includes two op amps in metal can packages.
Two other packages that look like integrated circuits each hold four transistors.
Next to them, a bullet-shaped Zener diode sets the output voltage level.
The large round switching power transistor is visible in the middle of the board.
You might expect the power supply to be a simple
buck converter.
However, the power supply uses a more complicated design to
provide electrical isolation between the spacecraft and the clock.
I'm not sure, though, why isolation was necessary.8
Board 1 implements a switching power supply to produce 5 volts for the clock.
Many of the components in the power supply look different from American components.
While American resistors are usually labeled with colored bands, the Soviet resistors are green cylinders with their values printed
on them.
The Soviet diodes have orange rectangular packages (below), unlike the usual cylindrical American diodes.
The power transistor in the middle of the board is round, lacking the metal flanges of American power transistors
in "TO-3" packages.
I don't think the Soviet packaging is better or worse, but it's interesting to see how components from the two countries diverged.
The power supply uses 1 amp diodes in rectangular orange packages. The "OC" indicates a higher-quality military part.
The second board is also part of the power supply, but is much simpler. It has inductors and capacitors to filter the power, as well as a linear voltage regulator chip (pink) to produce 15 volts for the op amp ICs in the first board.
The voltage regulator chip has two large metal tabs on the bottom that were soldered to the circuit board to dissipate heat.
Strangely, the board has three large holes in the right side.
The obvious explanation would be that these holes made room for tall components, a situation that arises on another board.
However, there are no components that fit the holes on this board.
Thus, I suspect this board was originally designed for a different device and reused in the clock.
Power supply board 2 is half-empty, with the right half apparently acting as a heat sink.
The remaining boards are filled with digital logic integrated circuits.
Board 3 (below) and board 5 (which is similar) implement the current time and alarm time functions.
Each board contains six BCD counter chips for the six digits (hours, minutes, and seconds).9
In addition, each digit counter requires a logic chip to control when it is incremented and another chip to control when it is reset, depending on whether the clock is being set or is running.
(This is one reason why so many chips are required.)
The pink chip on the board controls which digit is modified when setting the clock.10
Board 3 is filled with digital logic integrated circuits. Pins on either side connect the board to the wiring harnesses.
Board 4 (below) has two functions. First, it controls whether the clock displays the current time or the alarm time.
This is implemented with a selection chip for each digit.
Second, the board signals the spacecraft when the current time reaches the alarm time.
This is implemented with multiple chips to step through each digit, compare the times, and determine if they match.
Thus, even though the functions of this board seem simple, they require a whole board of chips.
The connections at the bottom of the board link board 4 to board 5. The board is connected to board 3 through the wiring harness.
Board 4 selects between the current time and the alarm time. It also compares the two values to determine when the alarm time has been reached.
Some of the boards have more circuitry than just digital logic.
For instance, boards 6 and 7 have pulse transformers to electrically isolate the control signals fed into the clock through the 19-pin connector.
(In modern circuits, this role would be performed by an optoisolator.)
These transformers look a bit like mushrooms or miniature water towers, and can be seen in the photo below.
Board 7 also has a quartz crystal, the metal rectangle below.11
Board 7 has a 1 MHz crystal that provides the timing signals for the clock. It also has three round pulse transformers that isolate the control signals from the spacecraft.
The two functions of board 7 (below) are to generate the clock's timing pulses and to implement the stopwatch.
The quartz crystal generates accurate 1 megahertz pulses.
These pulses are reduced to one-second pulses by six BCD counters;
each counter chip divides the frequency by 10.
These timing pulses are used by the rest of the clock.
To implement the stopwatch, the board has
four BCD counters for the four digits.
It also has control logic to start, stop, and reset the stopwatch.
The three pulse transformers allow the spacecraft to control the stopwatch when certain events happen.
Additional chips handle these mode changes.
Board 7 contains the stopwatch circuitry, as well as the quartz crystal that generates timings for the whole clock. Wires along the front connect the board to Board 6.
Boards eight and nine drive the LED displays.
Each LED digit requires a chip to illuminates the appropriate segments of the 7-segment LED based on the BCD (binary-coded decimal) value.
These BCD-to-7-segment driver chips are the pink 16-pin chips on the board.12
Since the clock displays 10 digits in total, 10 driver chips are used.
Eight driver chips are on board 8, while board 9 has two chips along with numerous current-limiting resistors for the LEDs.
The switches to control the clock are also visible in the photo below.
Board 8 is an LED driver board holding eight 7-segment driver chips. Board 9 (underneath) has two more driver chips and many resistors.
Finally, board 10 (below) holds the ten LED digits.
Each digit consists of a seven-segment LED, along with a comma. I think one of the commas is wired up to indicate something; we'll find out what
when we power up the clock.
Board 10 holds the ten LED digits. Photo from Marc Verdiell.
Soviet integrated circuits
Next, I'll discuss the integrated circuits used in the clock.
The clock is built mostly from TTL integrated circuits, a type of digital logic that was popular
in the 1970s through the 1990s.
(If you've done hobbyist digital electronics, you probably know the 7400-series of TTL chips.)
TTL chips were fast, inexpensive and reliable.
Their main drawback, however, was that a TTL chip didn't contain much functionality.
A basic TTL chip contained just a few logic gates, such as 4 NAND gates or 6 inverters, while
a more complex TTL chip implemented a functional unit such as a 4-bit counter.
Eventually, TTL lost out to CMOS chips (the chips in modern computers), which use much less power and are much
denser.
Because each chip in the Soyuz clock didn't do very much, the clock required many boards of chips to perform its functions.
For example, each digit of the clock requires a counter chip, as well as a couple of logic chips to increment and clear that digit as needed,
and a chip to drive the associated 7-segment LED display.
Since the clock displays 10 digits, that's 40 chips already.
Additional chips handle the buttons and switches, implement the alarm, keep track of the stopwatch state, run the oscillator, and so forth, pushing the total to over 100 chips.
One nice thing about Soviet ICs is that the part numbers are assigned according to a rational system, unlike the essentially random numbering of American integrated circuits.13
Two letters in the part number indicate the function of the chip, such as a logic gate, counter, flip flop, or decoder.
For example, the IC below is labeled "Δ134 ΛБ2A".
The series number, 134, indicates the chip is a low-power TTL chip.
The "Л" (L) indicates a logic chip (Логические), with "ЛБ" indicating NAND/NOR logic gates.
Finally, "2" indicates a specific chip in the ЛБ category.
(The 134ЛБ2 chip's functionality is two 4-input NAND gates and an inverter, a chip that doesn't have an American counterpart.)
14
Two integrated circuits inside the clock.
The logos on the integrated circuits reveal that they were
manufactured by a variety of companies.
Some of the chips in the clock are shown below,
along with the name of the manufacturer and its English translation.
More information on Soviet semiconductor logos can be found here and here.
By looking up the logo on each chip, the manufacturer can be determined.
Comparison with US technology
How does the Soyuz clock compare with US technology?
When I first looked at the clock I would have guessed it was manufactured in 1969, not 1984, based on the construction and the large number of simple flat-pack chips.
In comparison, American technology in 1984 produced the IBM PC/AT and the Apple Macintosh.
It seemed absurd for the clock to use boards full of TTL chips a decade after the US had produced single-chip digital watches.16
However, the comparison turned out to be not so simple.
To compare the Soyuz clock with contemporary 1980s American space electronics, I looked at a board from
the Space Shuttle's AP-101S computer.17
The photo below shows circuitry from the Soyuz clock (left) and the Shuttle computer (right).
Although the Shuttle computer is technologically more advanced, the gap was smaller than I expected.
Both systems were built from TTL chips, although the Shuttle computer used a faster generation of chips.
Many Shuttle chips are slightly more complex; note the larger 20-pin chips at the
top of the board.
The large white chip is significantly more complex; it is an AMD Am2960 memory error correction chip.
The Shuttle's printed-circuit board is more advanced, with multiple layers rather than two layers,
allowing the chips to be packed 50% more densely.
At the time, the USSR was estimated to be about 8 to 9 years behind the West in integrated circuit technology;15
this is in line with the differences I see between the two boards.
The Soyuz clock board (left) and Space Shuttle computer board (right), to the same scale. Both use surface-mount TTL chips.
What surprised me, though, was the similarities between the Shuttle computer and the Soviet clock.
I expected the Shuttle computer to use 1980s microprocessors and be a generation ahead of the Soyuz clock, but instead the two systems
both use TTL technology, and in many cases chips with almost identical functionality.
For example, both boards use chips that implement four NAND gates. (See if you can find the
134ΛБ1A chip on the left and the 54F00 on the right.)
Conclusion
Why does the Soyuz clock contain over 100 chips instead of being implemented with a single clock chip?
Soviet integrated circuit technology was about 8 years behind American technology and TTL chips were a reasonable choice at the time, even in the US.
Since each TTL chip doesn't do very much, it takes boards full of chips to implement even something simple like a clock.
The next step will be to power up the clock and see the clock in operation.
I've been studying the power supply so we can make this happen.
I plan to write more about the power supply and other parts of the clock,
so follow me @kenshirriff for details. also have an RSS feed.
Until then, you can watch Marc's video showing the disassembly of the space clock:
Notes and References
CuriousMarc obtained the clock from an auction and it
was advertised as flown to space, but I don't know which mission it was flown on.
The date codes on the components inside the clock are mostly from 1983, with one from 1984, so the clock was probably manufactured in 1984.
The Russian name for the clock is "Бортовые Часы Космические" (Onboard Space Clock), which is abbreviated as "БЧК". ↩
The photo of the Soyuz console was mislabeled as from Soyuz 7K-VI.
However, that mission was in the 1960s and the Soyuz-7K console was much different.
A photo of the Soyuz-7K console is in this Russian article. ↩
The digital clock was used in the Soyuz-TM version of the spacecraft.
This version of the console was known as Neptune (Нептун).
For details on Soyuz consoles, see
The Integrated Information Display System for the Soyuz-TMA.
Two Russian documents are
this and
(this.
The analog clock can be seen in a Scott Manley video here and in some
photos by Steve Jurvetson. ↩
Most of the description of how the clock works is based on my reverse engineering, so I don't guarantee that everything
in this post is accurate. When we power up the clock, I'll find out what I got wrong :-) ↩
The clock has the label "ЧТВ", which is an abbreviation for "Часы Текущего Времени".
The Soyuz Crew Ops Manual
translates this as "Clock of Current Time". ↩
The Soyuz Crew Ops Manual has some
information on the clock on page 35.
According to the manual, the stopwatch is
controlled automatically during the propulsion system engine burn timing, to measure the time between the
Engine Fire command and the Engine Cut Off command.
It also automatically measures the time during descent until contact. ↩
The 19-pin connector was a standard Soviet military connector of type RS19TV (РС19ТВ in Cyrillic).
I was able to find a matching connector on eBay, which we will use for powering the clock. ↩
Cell-phone chargers, for instance, use isolated power supplies for safety, to protect the user from the dangerous 120-volt line voltage.
The clock, however, is powered with 28 volts, so there's no obvious reason for electrical isolation.
(The Apollo Guidance Computer's power supply, for example,
used a non-isolated switching power supply.) ↩
The clock uses a BCD counter chip for each digit with some exceptions. The top hours digit only goes to "2" (for a 24-hour clock), so two flip flops are used instead of a counter. The top digit for minutes and seconds needs to roll over at 6 (i.e. 60 seconds/minutes), so
the clock uses a divide-by-12 chip similar to the 7492 chip.
(The chip can be configured to roll over at 6 rather than 12.) ↩
The pink chip on board 3 is a К134ИД6 decimal decoder, which selects one of 10 outputs based on the 4-bit BCD value fed into it.
(The part number ИД indicates a decoder, Дешифраторы.)
This chip is a copy of the American 74L42 chip.
For some reason, the 16-pin integrated circuits are in pink ceramic packages, while the more common 14-pin integrated circuits are
in metal packages. ↩
The Soyuz Crew Ops Manual
(page 35) specifies the clock's accuracy as 30 seconds per day, which isn't very good. In comparison, a low-cost Timex quartz watch
from the early 1970s was accurate within 15 seconds per month.
According to the manual, the clock could be synchronized to external time pulses.
During launch/injection and autonomous orbital flight phases, the clock
was synchronized to the
Program-Timing Control Equipment (АПВУ). It could also be synchronized to the TV unit (KЛ110). ↩
LED displays often use multiplexing, where one driver chip is shared across all the digits and the display rapidly cycles through
the digits.
This reduces the number of chips and resistors required. I'm not sure why the clock uses separate drivers instead of multiplexing. ↩
For more information on Soviet integrated circuits, including the ones used in the clock, see the databook Интегральные микросхемы и их зарубежные аналоги (Integrated circuits and their foreign counterparts). ↩
The Soviet IC designation system is described in detail on Wikipedia.
There are a few complications that make a chip's designation different from the labels printed on the chip.
Because Л and П (Cyrillic L and P) look similar on small chips,
the chip labels use Λ (Greek L) in place of Л (Cyrillic L).
The Greek D (Δ) may replace Cyrillic D (Д) to avoid confusion with Cyrillic А.
Moreover, names for commercial chips start with K, unlike the military chips used in the clock.
Thus, a chip labeled "Δ134 ΛБ2A" appears in databooks and on the web under the name "К134ЛБ2". ↩
Two CIA reports (1974 and 1986) provide information on the lag between Soviet IC technology and Western technology. ↩
US manufacturers implemented clocks on a single chip in the early 1970s.
Mostek introduced a single-chip digital clock chip in 1972, the Mostek MM5017.
In 1974,
Intel introduced a watch using a low-power CMOS chip, the
Intel 5810
In other words, the Soyuz clock could (roughly) have been replaced with a single chip a decade earlier. ↩
The AP-101S computer in the Space Shuttle was part of IBM's System/4π line of
avionics computers.
This 64-pound computer was built from TTL integrated circuits, using
the 74F00 series (Fairchild's FAST line) for improved performance.
(Its memory, however, was built from high-capacity CMOS chips.)
The AP-101S computer was an updated version of the AP-101B used in the earlier Space Shuttle flights.
(See The new AP101S general-purpose computer (GPC) for the space shuttle and
Space Shuttle Avionics Upgrade.)
At first, it surprised me that they designed both Shuttle computers from low-complexity TTL chips, but
it made sense when the design of the earlier AP-101B computer started in 1972.
Back in the 1970s, minicomputers were commonly built from TTL chips because
microprocessors were new and much slower than TTL.
The first Shuttle computer achieved a speed of
0.42 MIPS.
This performance was respectable in 1972 but poor by 1981, when the Shuttle first flew.
To improve performance, a redesign of the computer started in 1982.
The updated AP-101S computer stuck with TTL, so its performance improved only moderately, to 1.27 MIPS, slightly slower than
the Motorola 68010 (1982) which ran at 2.4 MIPS.
Unfortunately, the gap between TTL computers and microcomputers got exponentially worse, following Moore's law.
By 1991, when the AP-101S first flew, the Motorola 68040 ran at 44 MIPS.
And by the end of the Shuttle program in 2011, the Intel Core i7 processor ran at 100,000 MIPS,
many orders of magnitude faster than the Shuttle computer.
So why did the Space Shuttle use mostly-obsolete TTL technology in the 1980s redesign?
One reason was backward compatibility. Since the first Shuttle computer
used the proprietary IBM 4π architecture, it couldn't be replaced by an off-the-shelf microprocessor.
Reliability was another motivation for TTL. Commerical microprocessors weren't designed for the reliability needs of space systems and
lacked features such as radiation resistance and parity-protected caches.
Finally, the aerospace development cycle is very long; although the Shuttle computer redesign started in 1982, the computer wasn't used on a flight until 1991 and remained in use until 2011.
The point is that there were reasons to build aerospace systems from TTL, even though microprocessors were much
faster, more compact, and lower power. ↩
Front view of the igniter. The black text is hard to read under the brown front.
Oscilloscope trace pickingup electrical noise from the igniter over the air. Image from CuriousMarc's video.
Schematic of the spark generator.
