The first microcomputer: The transfluxor-powered Arma Micro Computer from 1962

What would you say is the first microcomputer?1 The Apple I from 1976? The Altair 8800 from 1974? Perhaps the lesser-known Micral N (1973) or Q1 (1972)? How about the Arma Micro Computer from way back in 1962. The Arma Micro Computer was a compact 20-pound transistorized computer, designed for applications in space such as inertial or celestial navigation, steering, radar, or engine control.

Obviously, the Arma Micro Computer is not a microcomputer according to modern definitions, since its processor was made from discrete components. But it's an interesting computer in many ways. First, it is an example of the aerospace computers of the 1960s, advanced systems that are now almost entirely forgotten. People think of 1960s computers as room-filling mainframes, but there was a whole separate world of cutting-edge miniaturized aerospace computers. (Taking up just 0.4 cubic feet, the Arma Micro Computer was smaller than an Apple II.) Second, the Arma Micro Computer used strange components such as transfluxors and had an unusual 22-bit serial architecture. Finally, the Arma Micro Computer evolved into a series of computers used on Navy ships and submarines, the E-2C Hawkeye airborne early warning plane, the Concorde, and even Air Force One.

The Arma Micro Computer

The Arma Micro Computer, with a circuit board on top. Click this image (or any other) for a larger version. Photo courtesy of Daniel Plotnick.

The Micro Computer used 22-bit words, which may seem like a strange size from the modern perspective. But there's no inherent need for a word size to be a power of 2. In particular, the Micro Computer was designed for mathematical calculations, not dealing with 8-bit characters. The word size was selected to provide enough accuracy for its navigational tasks.

Another strange aspect of the Micro Computer is that it was a serial machine, sequentially operating on one bit of a word at a time.2 This approach was often used in early machines because it substantially reduced the amount of hardware required: it only needs a 1-bit data bus and a 1-bit ALU. The downside is that a serial machine is much slower because each 22-bit word takes 22 clock cycles (plus 5 cycles of overhead). As a result, the Micro Computer executed just 36000 operations per second, despite its 1 megahertz clock speed.

Ad for the Arma Micro Computer (called the MICRO here). Source: Electronics, July 27, 1962.

The Micro Computer had a small instruction set of 19 instructions.3 It included multiply, divide, and square root, instructions that weren't implemented in early microprocessors. This illustrates how early microprocessors were a significant step backward in functionality. Moreover, the multiply, divide, and square root instructions used a separate arithmetic unit, so they could execute in parallel with other arithmetic instructions. Because the Micro Computer needed to interact with spacecraft systems, it had a focus on I/O, with 120 digital inputs or outputs, configured as needed for a particular mission.

Circuits

The Micro Computer was built from silicon transistors and diodes, using diode-transistor logic. The construction technique was somewhat unusual. The basic circuits were the flip-flop, the complementary buffer (i.e. an inverter), and the diode gate. Each basic circuit was constructed on a small wafer, .77 inches on a side.5 The photo below shows wafers for a two-transistor flip-flop and two diode gates. Each wafer had up to 16 connection tabs on the edges. These wafers are analogous to integrated circuits, but constructed from discrete components.

Three circuit modules from the Arma Micro Computer. Image from "The Arma Micro Computer for Space Applications".

The wafers were mounted on printed circuit boards, with up to 22 wafers on a board. Pairs of boards were mounted back to back with polyurethane foam between the boards to form a "sandwich", which was conformally coated. The result was a module that was protected against the harsh environment of a missile or spacecraft. The computer could handle a shock of 100 g's and temperatures of 0°C to 85°C as well as 100% humidity or a vacuum.

Because the Micro Computer was a serial machine, its bits were constantly moving. For register storage such as the accumulator, it used six magnetostrictive torsional delay lines, storing a sequence of bits as physical twists that formed pulses racing through a long coil of wire.

The photo below shows the Arma Micro Computer with the case removed. If you look closely, you can see the 22 small circuit wafers mounted on each printed circuit board. The memory driver boards and delay lines are towards the back, spaced more widely than the other printed circuit boards. The cable harness underneath the boards provides the connections between boards.4

Circuit boards inside the Arma Micro Computer. Photo courtesy of Daniel Plotnick.

Transfluxors

One of the most unusual parts of the Micro Computer was its storage. Computers at the time typically used magnetic core memory, with each bit stored in a tiny ferrite ring, magnetized either clockwise or counterclockwise to store a 0 or 1. One drawback of standard core memory was that the process of reading a core also cleared the core, requiring data to be written back after a read.

Diagram of Arma's memory system. From patent 3048828.

The Micro Computer used ferrite cores, but these were "two-aperture" cores, with a larger hole and a smaller hole, as shown above. Data is written to the "major aperture" and read from the "minor aperture". Although the minor aperture switches state and is erased during a read, the major aperture retains the bit, allowing the minor aperture to be switched back to its original state. Thus, unlike regular core memory, transfluxors don't lose their data when reading.

The resulting system is called non-destructive readout (NDRO), compared to the destructive readout (DRO) of regular core memory.6 The Micro Computer used non-destructive readout memory to ensure that the program memory remained uncorrupted. In contrast, if a program is stored in regular core memory, each instruction must be written back as it is executed, creating the possibility that a transient could corrupt the software. By using transfluxors, this possibility of error is eliminated. (In either case, core memory has the convenient property that data is preserved when power is removed, since data is stored magnetically. With modern semiconductor memory, you lose data when the power goes off.)

The photo below shows a compact transfluxor-based storage module used in the Micro Computer, holding 512 words. In total, the computer could hold up to 7808 words of program memory and 256 words of data memory. It appears that transfluxors didn't live up to their promise, since most computers used regular core memory until semiconductor memory took over in the early 1970s.

Transfluxor-based core memory module from the Arma Micro Computer. Image from "The Arma Micro Computer for Space Applications".

Arma's history and the path to the Micro Computer

The Arma Engineering Company was founded in 1918 and built advanced military equipment.7 Its first product was a searchlight for the Navy, followed by a gyroscopic compass and analog computers for naval gun targeting. In 1939, Arma produced the Torpedo Data Computer, a remarkable electromechanical analog computer. US submarines used this computer to track target ships and automatically aim torpedos. The Torpedo Data Computer performed complex trigonometric calculations and integration to account for the motion of the target ship and the submarine. While the Torpedo Data Computer performed well, the Navy's Mark 14 torpedo had many problems—running too deep, exploding too soon, or failing to explode—making torpedoes often ineffectual even with a perfect hit.

The Torpedo Data Computer Mark III in the USS Pampanito.

Arma underwent major corporate changes due to World War II. Before the war, the German-owned Bosch Company built vehicle starters and aircraft magnetos in the United States. When the US entered World War II in 1941, the government was concerned that a German-controlled company was manufacturing key military hardware so the Office of Alien Property Custodian took over the Bosch plant. In 1948, the banking group that controlled Arma bought Bosch from the Office of the Alien Property Custodian, merging them into the American Bosch Arma Corporation (AMBAC).8 (Arma had earlier received the rights to gyrocompass technology from the German Anschutz company, seized by the Navy after World War I, so Arma benefitted twice from wartime government seizures.)

In the mid-1950s, Arma moved into digital computers, building an inertial guidance computer for the Atlas nuclear missile program. America's first ICBM was the Atlas missile, which became operational in 1959. The first Atlas missiles used radio guidance from the launch site to direct the missile. Since radio signals could be jammed by the enemy, this wasn't a robust solution.

The solution to missile guidance was an inertial navigation system. By using sensitive gyroscopes and accelerometers, a missile could continuously track its position and velocity without any external input, making it unjammable. A key developer of this system was Arma's Wen Tsing Chow, one of the driving forces behind digital aviation computers. He faced extreme skepticism in the 1950s for the idea of putting a computer in a missile. One general mocked him, asking "Where are you going to put the five Harvard professors you'll need to keep it running?" But computerized navigation was successful and in 1961, the Atlas missile was updated to use the Arma inertial guidance computer. It was said to be the first production airborne digital computer.9 Wen Tsing Chow also invented the programmable read-only memory (PROM), allowing missile targeting information to be programmed into a computer outside the factory.

Wen Tsing Chow, computer engineer, with Arma Micro Computer. From Control Engineering, January 1963, page 19. Courtesy of Daniel Plotnick.

The photo below shows the Atlas ICBM's guidance system. The Arma W-107A computer is at the top and the gyroscopes are in the middle. This computer was an 18-bit serial machine running at 143.36 kHz. It ran a hard-wired program that integrated the accelerometer information and solved equations for the crossrange error function, range error function, and gravity, making these computations every half second.10 The computer weighed 240 pounds and consumed 1000 watts. The computer contained about 36,000 components: discrete transistors, diodes, resistors, and capacitors mounted on 9.5" × 6.5" printed-circuit boards. On the ground, the computer was air-cooled to 55 °F, but there was no cooling after launch as the computer only operated for five minutes of powered flight and wouldn't overheat during that time.

Guidance system for Atlas ICBM. From "Atlas Inertial Guidance System" by John Heiderstadt. Photo unclassified in 1967.

The Atlas wasn't originally designed for a computerized guidance system so there wasn't room inside the missile for the computer. To get around this, a large pod was stuck on the side of the missile to hold the computer and gyroscopes, as indicated in the photo below. This doesn't look aerodynamic, but I guess it worked.

Atlas missile. Arrow indicates the pod containing the Arma guidance computer and inertial navigation system. Original photo by Robert DuHamel, CC BY-SA 3.0.

The Atlas guidance computer (left, below) consisted of three aluminum sections called "decks". The top deck held two replaceable target constant units, each providing 54 navigation constants that specified a target. The constants were stored in a stack of printed circuit boards 16" × 8" × 1.5", covered in over a thousand diodes, Wen Tsing Chow's PROM memory. A target was programmed into the stack by a rack of equipment that would selectively burn out diodes, changing the corresponding bit to a 1. (This is why programming a PROM is referred to as "burning the PROM".11) The diode matrix was later replaced with a transfluxor memory array, which had the advantage that it could be reprogrammed as necessary. The top deck also had connectors for the accelerometer inputs, the outputs, and connections for ground support equipment. The bottom deck had power connectors for 28 volts DC and 115V 400 Hz 3-phase AC. In the bottom deck, quartz delay lines were used for storage, representing bits as acoustic waves. Twelve circuit cards, each with a faceted quartz block four inches in diameter, provided a total of 32 words of storage.

Three generations of Arma Computers: the W-107A Atlas ICBM guidance computer, the Lightweight Airborne Digital Computer, and the Arma Micro Computer (perhaps a prototype). Photo courtesy of Daniel Plotnick.

Arma considered the Micro Computer the third generation of its airborne computers. The first generation was the Atlas guidance computer, constructed from germanium transistors and diodes (in the pre-silicon era). The second-generation computer moved to silicon transistors and diodes. The third-generation computers still used discrete components, but mounted on the small square wafers. The third generation also had a general-purpose architecture and programmable transfluxor memory instead of a hard-wired program.

After the Micro Computer

Arma continued to develop computers, improving the Arma Micro Computer. The Micro C computer (1965) was developed for Navy ships and submarines. Much like the original Micro, the Micro C used transfluxor storage, but increased the clock frequency to 972 kHz. The computer was much larger: 3.87 cubic feet and 150 pounds. This description states that "the machine is an outgrowth of the ARMA product line of micro computers and is logically and electrically similar to micro-computers designed for missile environments."

Module from the Arma Micro-C Computer. Photo courtesy of Daniel Plotnick.

In mid-1966, Arma introduced the Micro D computer, built from TTL integrated circuits. Like the original Micro, this computer was serial, but the Micro D had a word length of 18 bits and ran at 1.5 MHz. It weighed 5.25 pounds and was very compact, just 0.09 ft³. Instead of transfluxors, the Micro D used regular magnetic core memory, 4K to 31K words.

The Arma Micro-D 1801 computer. The 1808 was a slightly larger model. Photo courtesy of Daniel Plotnick.

The widely-used Litton LTN-51 inertial navigation system was built around the Arma Micro-D computer.12 This navigation system was designed for commercial aircraft, but was also used for military applications, ships, and NASA aircraft. Aircraft from early Concordes to Air Force One used the LTN-51 for navigation. The photo below shows a navigation unit with the Arma Micro-D computer in the lower left and the gyroscope unit on the right.

Litton LTN-51 inertial navigation system. Photo courtesy of pascal mz, concordescopia.com.

In early 1968, the Arma Portable Micro D was introduced, a 14-pound battery-powered computer also called the Celestial Data Processor. This handheld computer was designed for navigation in crewed earth orbital flight, determining orbital parameters from stadimeter and sextant measurements performed by astronauts. As far as I can tell, this computer never made it beyond the prototype stage.

The Arma Celestial Data Processor (source).

Conclusions

The Arma Micro Computer is just one of the dozens of compact aerospace computers of the 1960s, a category that is mostly forgotten and ignored. Another example is the Delco MAGIC I (1961), said to be the "first complete airborne computer to have its logic functions mechanized exclusively with integrated circuits". IBM's 4 Pi series started in 1966 and was used in many systems from the F-15 to the Space Shuttle. By 1968, denser MOS/LSI chips were used in general-purpose aerospace computers such as the Rockwell MOS GP and the Texas Instruments Model 2502 LSI Computer. 13

Arma also illustrates that a company can be on the cutting edge of technology for decades and then suddenly go out of business and be forgotten. After some struggles, Arma was acquired by United Technologies in 1978 for $210 million and was then shut down in 1982. (The German Bosch corporation remains, now a large multinational known for products such as dishwashers, auto parts, and power tools.) Looking at a list of aerospace computers shows many innovative but vanished companies: Univac, Burroughs, Sperry (now all Unisys), AC Electronics (now part of Raytheon), Autonetics (acquired by Boeing), RCA (bought by GE), and TRW (acquired by Northrop Grumman).

Finally, the Micro Computer illustrates that terms such as "microcomputer" are not objective categories but are social constructs. At first, it seems obvious that the Arma Micro Computer is not a real microcomputer. If you consider a microcomputer to be a computer built around a microprocessor, that's true. (Although "microprocessor" is also not as clear as you might think.) But a microcomputer can also be defined as "A small computer that includes one or more input/output units and sufficient memory to execute instructions" (according to the IBM Dictionary of Computing, 1994)14 and the Arma Micro Computer meets that definition. The "microcomputer" is a shifting concept, changing from the 1960s to the 1990s to today.

For more, follow me on Twitter @kenshirriff or RSS for updates. I'm also on Mastodon as @[email protected]. Thanks to Daniel Plotnick for providing a great deal of information and photos. Thanks to John Hartman for obtaining an obscure conference proceedings for me.

Notes and references

1. I should mention the danger of "firsts" from a historical perspective. Historian Michael Williams advised "not to use the word 'first'" and said, "If you add enough adjectives to a description you can always claim your own favorite." (See ENIAC in Action, p7.)

   The first usage of "micro-computer" that I could find is from 1956. In Isaac Asimov's short story "The Dying Night", he mentions a "micro-computer" in passing: "In recent years, it [the handheld scanner] had become the hallmark of the scientist, much as the stethoscope was that of the physician and the micro-computer that of the statistician."

   Another interesting example of a "micro-computer" is the Texas Instruments Semiconductor Network Computer. This palm-sized computer is often considered the first integrated-circuit computer. It was an 11-bit serial computer running at 100 kHz, built out of RS flip-flops, NOR gates, and logic drivers. The 1961 article below described this computer as a "micro-computer", although this was a one-off use of the term, not the computer's name. This brochure describes the Semiconductor Network Computer in more detail and Semiconductor Networks are described in detail in this article. Unlike modern ICs, these integrated circuits used flying wires for internal connections rather than a deposited metal layer, making their design a dead end.

   

   The Texas Instruments Semiconductor Network Computer. From Computers and Automation, Dec. 1961.

    ↩

2. Most of the information on the Arma Micro Computer in this article is from "The Arma Micro Computer for Space Applications", by E. Keonjian and J. Marx, Spaceborne Computing Engineering Conference, 1962, pages 103-116. ↩

3. The Arma Micro Computer's instruction set consisted of 19 22-bit instructions, shown below.

   

   Instruction set of the Arma Micro Computer. Figure from "The Arma Micro Computer for Space Applications".

    ↩

4. This block diagram shows the structure of the Micro Computer. The accumulator register (AC) is used for all data transfers as well as addition and subtraction. The multiply-divide register is used for multiplication, division, and square roots. The product register (PR), quotient register (QR), and square root register (SR) are used by the corresponding instructions. The data buffer register (S) holds data moving in or out of storage; it is shown with two 11-bit parts.

   

   Block diagram of the Arma Micro Computer. Figure from "The Arma Micro Computer for Space Applications".

   For control logic, the location counter (L) is the 13-bit program counter. For a subroutine call, the current address can be stored in the recall register (RR), which acts as a link register to hold the return address. (The RR is not shown on the diagram because it is held in memory.) Instruction decoding uses the instruction register (I), with the next instruction in the instruction buffer (B). The operand register (P) contains the 13-bit address from an instruction, while the remaining register (R) is used for I/O addressing. ↩

5. Arma's original plan was to mount circuits on ceramic wafers. Resistors would be printed onto the wafer and wiring silk-screened. (This is similar to IBM's SLT modules (1964), although IBM mounted diode and transistors as bare dies rather than components.) However, the Micro Computer ended up using epoxy-glass wafers with small, but discrete components: standard TO-46 transistors, "fly-speck" diodes, and 1/10 watt resistors. I don't see much advantage to these wafers over mounting the components directly on the printed-circuit board; maybe standardization is the benefit. ↩

6. The Micro Computer used an unusual mechanism to select a word to read or write. Most computers used a grid of selection wires; by energizing an X and a Y wire at the same time, the corresponding core was selected. The key idea of this "coincident-current" approach is that each wire has half the current necessary to flip a core, so the core with the energized X and Y wires will have enough current to flip. This puts tight constraints on the current level, since too much current will flip all the cores along the wire, but not enough current will not flip the selected core. What makes this difficult is that the properties of a core change with temperature, so either the cores need to be temperature-stabilized or the current needs to be adjusted based on the temperature.

   The Micro Computer instead used a separate wire for each word, so as long as the current is large enough, the cores will flip. This approach avoids the issues with temperature sensitivity, an important concern for a computer that needs to handle the large temperature swings of a spacecraft, not an air-conditioned data center. Unfortunately, it requires much more wiring. Specifically, the large advantage of the coincident-current approach is that an N×N grid of wires lets you select N² words. With the Micro Computer approach, N wires only select N words, so the scalability is much worse.

   For more on Arma's memory systems, see patents: Memory Device, 3048828 and Multiaperture Core Memory Matrix, 3289181. ↩

7. The capitalization of Arma vs. ARMA is inconsistent. It often appears in all-caps, but both forms are used, sometimes in the same article. "Arma" is not an acronym; the name came from the names of its founders: Arthur Davis and David Mahood (source: Between Human and Machine, p54). I suspect a 1960s corporate branding effort was responsible for the use of all-caps. ↩

8. For more on the corporate history of Arma, see IRE Pulse, March 1958, p9-10. Details of corporate politics and what went wrong are here. More information on the financial ups and downs of Arma is in "Charles Perelle's Spacemanship", Fortune, January 1959, an article that focused on Charles Perelle, the president of American Bosch Arma. ↩

9. Wikipedia says that Arma's guidance computer was "the first production airborne digital computer". However, the Hughes Digitair (1958) has also been called "the first airborne digital computer in actual production." Another source says the Arma computer was the "first all-solid-state, high-reliability, space-borne digital computer." The TRADIC (Transistorized Airborne Digital Computer) (1954) was earlier, but was a prototype system, not a production system. In turn, the TRADIC is said by some to be the first fully transistorized computer, but that depends on exactly how you interpret "fully".

   This is another example of how the "first" depends on the specific adjectives used. ↩

10. The information on the Arma W-107A computer is from "Atlas Inertial Guidance System: As I Remember It" by Principal Engineer John Heiderstadt. ↩

11. Chow Wen Tsing's PROM patent discusses the term "burning", explaining that it refers to burning out the diodes electrically. To widen the patent, he clarifies that "The term 'blowing out' or 'burning out' further includes any process which, by means less drastic than actual destruction of the non-linear elements, effects a change of the circuit impedance to a level which makes the particular circuit inoperative." This description prevented someone from trying to get around the patent by stating that nothing was really burning. ↩

12. Details on the LTN-51 navigation system and its uses are in this document. ↩

13. For more information on early aerospace computers, see State-of-the-art of Aerospace Digital Computers (1967), updated as Trends in Aerospace Digital Computer Design (1969). Also see the 1970 Survey of Military CPUs. Efficient partitioning for the batch-fabricated fourth generation computer (1968) discusses how "The computer industry is on the verge of an upheaval" from new hardware including LSI and fast ROMs, and describes various LSI aerospace computers. ↩

14. The "IBM Dictionary of Computing" (1994) has two definitions of "microcomputer": "(1) A digital computer whose processing unit consists of one or more microprocessors, and includes storage and input/output facilities. (2) A small computer that includes one or more input/output units and sufficient memory to execute instructions; for example a personal computer. The essential components of a microcomputer are often contained within a single enclosure." The latter definition was from an ISO/IEC draft standard for terminology so it is somewhat "official". ↩

Reverse-engineering the Globus INK, a Soviet spaceflight navigation computer

One of the most interesting navigation instruments onboard Soyuz spacecraft was the Globus INK,1 which used a rotating globe to indicate the spacecraft's position above the Earth. This electromechanical analog computer used an elaborate system of gears, cams, and differentials to compute the spacecraft's position. The globe rotates in two dimensions: it spins end-over-end to indicate the spacecraft's orbit, while the globe's hemispheres rotate according to the Earth's daily rotation around its axis.2 The spacecraft's position above the Earth was represented by the fixed crosshairs on the plastic dome. The Globus also has latitude and longitude dials next to the globe to show the position numerically, while the light/shadow dial below the globe indicated when the spacecraft would enter or leave the Earth's shadow.

The INK-2S "Globus" space navigation indicator.

Opening up the Globus reveals that it is packed with complicated gears and mechanisms. It's amazing that this mechanical technology was used from the 1960s into the 21st century. But what are all those gears doing? How can orbital functions be implemented with gears? To answer these questions, I reverse-engineered the Globus and traced out its system of gears.

The Globus with the case removed, showing the complex gearing inside.

The diagram below summarizes my analysis. The Globus is an analog computer that represents values by rotating shafts by particular amounts. These rotations control the globe and the indicator dials. The flow of these rotational signals is shown by the lines on the diagram. The computation is based around addition, performed by ten differential gear assemblies. On the diagram, each "⨁" symbol indicates one of these differential gear assemblies. Other gears connect the components while scaling the signals through various gear ratios. Complicated functions are implemented with three specially-shaped cams. In the remainder of this blog post, I will break this diagram down into functional blocks and explain how the Globus operates.

This diagram shows the interconnections of the gear network in the Globus.

For all its complexity, though, the functionality of the Globus is pretty limited. It only handles a fixed orbit at a specific angle, and treats the orbit as circular. The Globus does not have any navigation input such as an inertial measurement unit (IMU). Instead, the cosmonauts configured the Globus by turning knobs to set the spacecraft's initial position and orbital period. From there, the Globus simply projected the current position of the spacecraft forward, essentially dead reckoning.

A closeup of the gears inside the Globus.

The globe

On seeing the Globus, one might wonder how the globe is rotated. It may seem that the globe must be free-floating so it can rotate in two axes. Instead, a clever mechanism attaches the globe to the unit. The key is that the globe's equator is a solid piece of metal that rotates around the horizontal axis of the unit. A second gear mechanism inside the globe rotates the globe around the North-South axis. The two rotations are controlled by concentric shafts that are fixed to the unit. Thus, the globe has two rotational degrees of freedom, even though it is attached at both ends.

The photo below shows the frame that holds and controls the globe. The dotted axis is fixed horizontally in the unit and rotations are fed through the two gears at the left. One gear rotates the globe and frame around the dotted axis, while the gear train causes the globe to rotate around the vertical polar axis (while the equator remains fixed).

The axis of the globe is at 51.8° to support that orbital inclination.

The angle above is 51.8° which is very important: this is the inclination of the standard Soyuz orbit. As a result, simply rotating the globe around the dotted line causes the crosshair to trace the orbit.3 Rotating the two halves of the globe around the poles yields the different paths over the Earth's surface as the Earth rotates. An important consequence of this design is that the Globus only supports a circular orbit at a fixed angle.

Differential gear mechanism

The primary mathematical element of the Globus is the differential gear mechanism, which can perform addition or subtraction. A differential gear takes two rotations as inputs and produces the (scaled) sum of the rotations as the output. The photo below shows one of the differential mechanisms. In the middle, the spider gear assembly (red box) consists of two bevel gears that can spin freely on a vertical shaft. The spider gear assembly as a whole is attached to a horizontal shaft, called the spider shaft. At the right, the spider shaft is attached to a spur gear (a gear with straight-cut teeth). The spider gear assembly, the spider shaft, and the spider's spur gear rotate together as a unit.

Diagram showing the components of a differential gear mechanism.

At the left and right are two end gear assemblies (yellow). The end gear is a bevel gear with angled teeth to mesh with the spider gears. Each end gear is locked to a spur gear and these gears spin freely on the horizontal spider shaft. In total, there are three spur gears: two connected to the end gears and one connected to the spider assembly. In the diagrams, I'll use the symbol below to represent the differential gear assembly: the end gears are symmetric on the top and bottom, with the spider shaft on the side. Any of the three spur gears can be used as an output, with the other two serving as inputs.

The symbol for the differential gear assembly.

To understand the behavior of the differential, suppose the two end gears are driven in the same direction at the same rate, say upwards.4 These gears will push on the spider gears and rotate the spider gear assembly, with the entire differential rotating as a fixed unit. On the other hand, suppose the two end gears are driven in opposite directions. In this case, the spider gears will spin on their shaft, but the spider gear assembly will remain stationary. In either case, the spider gear assembly motion is the average of the two end gear rotations, that is, the sum of the two rotations divided by 2. (I'll ignore the factor of 2 since I'm ignoring all the gear ratios.) If the operation of the differential is still confusing, this vintage Navy video has a detailed explanation.

The controls and displays

The diagram below shows the controls and displays of the Globus. The rotating globe is the centerpiece of the unit. Its plastic cover has a crosshair that represents the spacecraft's position above the Earth's surface. Surrounding the globe itself are dials that show the longitude, latitude, and the time before entering light and shadow. The cosmonauts manually initialize the globe position with the concentric globe rotation knobs: one rotates the globe along the orbital path while the other rotates the hemispheres. The mode switch at the top selects between the landing position mode, the standard Earth orbit mode, and turning off the unit. The orbit time adjustment configures the orbital time period in minutes while the orbit counter below it counts the number of orbits. Finally, the landing point angle sets the distance to the landing point in degrees of orbit.

The Globus with the controls labeled.

Computing the orbit time

The primary motion of the Globus is the end-over-end rotation of the globe showing the movement of the spacecraft in orbit. The orbital motion is powered by a solenoid at the top of the Globus that receives pulses once a second and advances a ratchet wheel (video).5 This wheel is connected to a complicated cam and differential system to provide the orbital motion.

The orbit solenoid (green) has a ratchet that rotates the gear to the right. The shaft connects it to differential gear assembly 1 at the bottom right.

Each orbit takes about 92 minutes, but the orbital time can be adjusted by a few minutes in steps of 0.01 minutes6 to account for changes in altitude. The Globus is surprisingly inflexible and this is the only orbital parameter that can be adjusted.7 The orbital period is adjusted by the three-position orbit time switch, which points to the minutes, tenths, or hundredths. Turning the central knob adjusts the indicated period dial.

The problem is how to generate the variable orbital rotation speed from the fixed speed of the solenoid. The solution is a special cam, shaped like a cone with a spiral cross-section. Three followers ride on the cam, so as the cam rotates, the follower is pushed outward and rotates on its shaft. If the follower is near the narrow part of the cam, it moves over a small distance and has a small rotation. But if the follower is near the wide part of the cam, it moves a larger distance and has a larger rotation. Thus, by moving the follower to a particular point on the cam, the rotational speed of the follower is selected. One follower adjusts the speed based on the minutes setting with others for the tenths and hundredths of minutes.

A diagram showing the orbital speed control mechanism. The cone has three followers, but only two are visible from this angle. The "transmission" gears are moved in and out by the outer knob to select which follower is adjusted by the inner knob.

Of course, the cam can't spiral out forever. Instead, at the end of one revolution, its cross-section drops back sharply to the starting diameter. This causes the follower to snap back to its original position. To prevent this from jerking the globe backward, the follower is connected to the differential gearing via a slip clutch and ratchet. Thus, when the follower snaps back, the ratchet holds the drive shaft stationary. The drive shaft then continues its rotation as the follower starts cycling out again. Each shaft output is accordingly a (mostly) smooth rotation at a speed that depends on the position of the follower.

A cam-based system adjusts the orbital speed using three differential gear assemblies.

The three adjustment signals are scaled by gear ratios to provide the appropriate contribution to the rotation. As shown above, the adjustments are added to the solenoid output by three differentials to generate the orbit rotation signal, output from differential 3.8 This signal also drives the odometer-like orbit counter on the front of the Globus. The diagram below shows how the components are arranged, as viewed from the back.

A back view of the Globus showing the orbit components.

Displaying the orbit rotation

Since the Globus doesn't have any external position input such as inertial guidance, it must be initialized by the cosmonauts. A knob on the front of the Globus provides manual adjustment of the orbital position. Differential 4 adds the knob signal to the orbit output discussed above.

The orbit controls drive the globe's motion.

The Globus has a "landing point" mode where the globe is rapidly rotated through a fraction of an orbit to indicate where the spacecraft would land if the retro-rockets were fired. Turning the mode switch caused the globe to rotate until the landing position was under the crosshairs and the cosmonauts could evaluate the suitability of this landing site. This mode is implemented with a landing position motor that provides the rapid rotation. This motor also rotates the globe back to the orbital position. The motor is driven through an electronics board with relays and a transistor, controlled by limit switches. I discussed the electronics in a previous post so I won't go into more details here. The landing position motor feeds into the orbit signal through differential 5, producing the final orbit signal.

The landing position motor and its associated gearing. The motor speed is geared down and then fed through a worm gear (upper center).

The orbit signal from differential 5 is used in several ways. Most importantly, the orbit signal provides the end-over-end rotation of the globe to indicate the spacecraft's travel in orbit. As discussed earlier, this is accomplished by rotating the globe's metal frame around the horizontal axis. The orbital signal also rotates a potentiometer to provide an electrical indication of the orbital position to other spacecraft systems.

The light/shadow indicator

Docking a spacecraft is a tricky endeavor, best performed in daylight, so it is useful to know how much time remains until the spacecraft enters the Earth's shadow. The light/shadow dial under the globe provides this information. This display consists of two nested wheels. The outer wheel is white and has two quarters removed. Through these gaps, the partially-black inner wheel is exposed, which can be adjusted to show 0% to 50% dark. This display is rotated by the orbital signal, turning half a revolution per orbit. As the spacecraft orbits, this dial shows the light/shadow transition and the time to the transistion.9

The light/shadow indicator, viewed from the underside of the Globus. The shadow indicator has been set to 35% shadow. Near the hub, a pin restricts motion of the inner wheel relative to the outer wheel.

You might expect the orbit to be in the dark 50% of the time, but because the spacecraft is about 200 km above the Earth's surface, it will sometimes be illuminated when the surface of the Earth underneath is dark.10 In the ground track below, the dotted part of the track is where the spacecraft is in the Earth's shadow; this is considerably less than 50%. Also note that the end of the orbit doesn't match up with the beginning, due to the Earth's rotation during the orbit.

Ground track of an Apollo-Soyuz Test Project orbit, corresponding to this Globus. Image courtesy of heavens-above.com.

The latitude indicator

The latitude indicator to the left of the globe shows the spacecraft's latitude. The map above shows how the latitude oscillates between 51.8°N and 51.8°S, corresponding to the launch inclination angle. Even though the path around the globe is a straight (circular) line, the orbit appears roughly sinusoidal when projected onto the map.11 The exact latitude is a surprisingly complicated function of the orbital position.12 This function is implemented by a cam that is attached to the globe. The varying radius of the cam corresponds to the function. A follower tracks the profile of the cam and rotates the latitude display wheel accordingly, providing the non-linear motion.

A cam is attached to the globe and rotates with the globe.

The Earth's rotation

The second motion of the globe is the Earth's daily rotation around its axis, which I'll call the Earth rotation. The Earth rotation is fed into the globe through the outer part of a concentric shaft, while the orbital rotation is provided through the inner shaft. The Earth rotation is transferred through three gears to the equatorial frame, where an internal mechanism rotates the hemispheres. There's a complication, though: if the globe's orbital shaft turns while the Earth rotation shaft remains stationary, the frame will rotate, causing the gears to turn and the hemispheres to rotate. In other words, keeping the hemispheres stationary requires the Earth shaft to rotate with the orbit shaft.

A closeup of the gear mechanisms that drive the Globus, showing the concentric shafts that control the two rotations.

The Globus solves this problem by adding the orbit rotation to the Earth rotation, as shown in the diagram below, using differentials 7 and 8. Differential 8 adds the normal orbit rotation, while differential 7 adds the orbit rotation due to the landing motor.14

The mechanism to compute the Earth's rotation around its axis.

The Earth motion is generated by a second solenoid (below) that is driven with one pulse per second.13 This motion is simpler than the orbit motion because it has a fixed rate. The "Earth" knob on the front of the Globus permits manual rotation around the Earth's axis. This signal is combined with the solenoid signal by differential 6. The sum from the three differentials is fed into the globe, rotating the hemispheres around their axis.

This solenoid, ratchet, and gear on the underside of the Globus drive the Earth rotation.

The solenoid and differentials are visible from the underside of the Globus. The diagram below labels these components as well as other important components.

The underside of the Globus.

The longitude display

The longitude cam and the followers that track its radius.

The longitude display is more complicated than the latitude display because it depends on both the Earth rotation and the orbit rotation. Unlike the latitude, the longitude doesn't oscillate but increases. The longitude increases by 360° every orbit according to a complicated formula describing the projection of the orbit onto the globe. Most of the time, the increase is small, but when crossing near the poles, the longitude changes rapidly. The Earth's rotation provides a smaller but steady negative change to the longitude.

The computation of the longitude.

The diagram above shows how the longitude is computed by combining the Earth rotation with the orbit rotation. Differential 9 adds the linear effect of the orbit on longitude (360° per orbit) and subtracts the effect of the Earth's rotation (360° per day). The nonlinear effect of the orbit is computed by a cam that is rotated by the orbit signal. The shape of the cam is picked up and fed into differential 10, computing the longitude that is displayed on the dial. The differentials, cam, and dial are visible from the back of the Globus (below).

A closeup of the differentials from the back of the Globus.

The time-lapse video below demonstrates the behavior of the rotating displays. The latitude display on the left oscillates between 51.8°N and 51.8°S. The longitude display at the top advances at a changing rate. Near the equator, it advances slowly, while it accelerates near the poles. The light/shadow display at the bottom rotates at a constant speed, completing half a revolution (one light/shadow cycle) per orbit.

Conclusions

The Globus INK is a remarkable piece of machinery, an analog computer that calculates orbits through an intricate system of gears, cams, and differentials. It provided astronauts with a high-resolution, full-color display of the spacecraft's position, way beyond what an electronic space computer could provide in the 1960s.

The drawback of the Globus is that its functionality is limited. Its parameters must be manually configured: the spacecraft's starting position, the orbital speed, the light/shadow regions, and the landing angle. It doesn't take any external guidance inputs, such as an IMU (inertial measurement unit), so it's not particularly accurate. Finally, it only supports a circular orbit at a fixed angle. While a more modern digital display lacks the physical charm of a rotating globe, the digital solution provides much more capability.

I recently wrote blog posts providing a Globus overview and the Globus electronics. Follow me on Twitter @kenshirriff or RSS for updates. I've also started experimenting with Mastodon recently as @[email protected]. Many thanks to Marcel for providing the Globus. I worked on this with CuriousMarc, so check out his Globus videos.

Notes and references

1. In Russian, the name for the device is "Индикатор Навигационный Космический" abbreviated as ИНК (INK). This translates to "space navigation indicator." but I'll use the more descriptive nickname "Globus" (i.e. globe). The Globus has a long history, back to the beginnings of Soviet crewed spaceflight. The first version was simpler and had the Russian acronym ИМП (IMP). Development of the IMP started in 1960 for the Vostok (1961) and Voshod (1964) spaceflights. The more complex INK model (described in this blog post) was created for the Soyuz flights, starting in 1967. The landing position feature is the main improvement of the INK model. The Soyuz-TMA (2002) upgraded to the Neptun-ME system which used digital display screens and abandoned the Globus. ↩

2. According to this document, one revolution of the globe relative to the axis of daily rotation occurs in a time equal to a sidereal day, taking into account the precession of the orbit relative to the earth's axis, caused by the asymmetry of the Earth's gravitational field. (A sidereal day is approximately 4 minutes shorter than a regular 24-hour day. The difference is that the sidereal day is relative to the fixed stars, rather than relative to the Sun.) ↩

3. To see how the angle between the poles and the globe's rotation results in the desired orbital inclination, consider two limit cases. First, suppose the angle between is 90°. In this case, the globe is "straight" with the equator horizontal. Rotating the globe along the horizontal axis, flipping the poles end-over-end, will cause the crosshair to trace a polar orbit, giving the expected inclination of 90°. On the other hand, suppose the angle is 0°. In this case, the globe is "sideways" with the equator vertical. Rotating the globe will cause the crosshair to remain over the equator, corresponding to an equatorial orbit with 0° inclination. ↩

4. There is a bit of ambiguity when describing the gear motions. If the end gears are rotating upwards when viewed from the front, the gears are both rotating clockwise when viewed from the right, so I'm referring to them as rotating in the same direction. But if you view each gear from its own side, the gear on the left is turning counterclockwise, so from that perspective they are turning in opposite directions. ↩

5. The solenoids are important since they provide all the energy to drive the globe. One of the problems with gear-driven analog computers is that each gear and shaft has a bit of friction and loses a bit of torque, and there is nothing to amplify the signal along the way. Thus, the 27-volt solenoids need to provide enough force to run the entire system. ↩

6. The orbital time can be adjusted between 86.85 minutes and 96.85 minutes according to this detailed page that describes the Globus in Russian. ↩

7. The Globus is manufactured for a particular orbital inclination, in this case 51.8°. The Globus assumes a circular orbit and does not account for any variations. The Globus does not account for any maneuvering in orbit. ↩

8. The outputs from the orbit cam are fed into the overall orbit rotation, which drives the orbit cam. This may seem like an "infinite loop" since the outputs from the cam turn the cam itself. However, the outputs from the cam are a small part of the overall orbit rotation, so the feedback dies off. ↩

9. The scales on the light/shadow display are a bit confusing. The inner scale (blue) is measured in percentage of an orbit, up to 100%. The fixed outer scale (red) measures minutes, indicating how many minutes until the spacecraft enters or leaves shadow. The spacecraft completes 100% of an orbit in about 90 minutes, so the scales almost, but not quite, line up. The wheel is driven by the orbit mechanism and turns half a revolution per orbit.

   

   The light and shadow indicator is controlled by two knobs.

    ↩

10. The Internation Space Station illustrates how an orbiting spacecraft is illuminated more than 50% of the time due to its height. You can often see the ISS illuminated in the nighttime sky close to sunset and sunrise (link). ↩

11. The ground track on the map is roughly, but not exactly, sinusoidal. As the orbit swings further from the equator, the track deviates more from a pure sinusoid. The shape will depend, of course, on the rectangular map projection. For more information, see this StackExcahnge post. ↩

12. To get an idea of how the latitude and longitude behave, consider a polar orbit with 90° angle of inclination, one that goes up a line of longitude, crosses the North Pole, and goes down the opposite line of latitude. Now, shift the orbit away from the poles a bit, but keeping a great circle. The spacecraft will go up, nearly along a constant line of longitude, with the latitude increasing steadily. As the spacecraft reaches the peak of its orbit near the North Pole, it will fall a bit short of the Pole but will still rapidly cross over to the other side. During this phase, the spacecraft rapidly crosses many lines of longitude (which are close together near the Pole) until it reaches the opposite line of longitude. Meanwhile, the latitude stops increasing short of 90° and then starts dropping. On the other side, the process repeats, with the longitude nearly constant while the latitude drops relatively constantly.

    The latitude and longitude are generated by complicated trigonometric functions. The latitude is given by arcsin(sin i * sin (2πt/T)), while the longitude is given by λ = arctan (cos i * tan(2πt/T)) + Ωt + λ₀, where t is the spaceship's flight time starting at the equator, i is the angle of inclination (51.8°), T is the orbital period, Ω is the angular velocity of the Earth's rotation, and λ₀ is the longitude of the ascending node. ↩

13. An important function of the gears is to scale the rotations as needed by using different gear ratios. For the most part, I'm ignoring the gear ratios, but the Earth rotation gearing is interesting. The gear driven by the solenoid has 60 teeth, so it rotates exactly once per minute. This gear drives a shaft with a very small gear on the other end with 15 teeth. This gear meshes with a much larger gear with approximately 75 teeth, which will thus rotate once every 5 minutes. The other end of that shaft has a gear with approximately 15 teeth, meshed with a large gear with approximately 90 teeth. This divides the rate by 6, yielding a rotation every 30 minutes. The sequence of gears and shafts continues, until the rotation is reduced to once per day. (The tooth counts are approximate because the gears are partially obstructed inside the Globus, making counting difficult.) ↩

14. There's a potential simplification when canceling out the orbital shaft rotation from the Earth rotation. If the orbit motion was taken from differential 5 instead of differential 4, the landing motor effect would get added automatically, eliminating the need for differential 7. I think the landing motor motion was added separately so the mechanism could account for the Earth's rotation during the landing descent. ↩

Reverse-engineering the electronics in the Globus analog navigational computer

In the Soyuz space missions, cosmonauts tracked their position above the Earth with a remarkable electromechanical device with a rotating globe. This navigation instrument was an analog computer that used an elaborate system of gears, cams, and differentials to compute the spacecraft's position. Officially, the unit was called a "space navigation indicator" with the Russian acronym ИНК (INK),1 but I'll use the nickname "Globus".

The INK-2S "Globus" space navigation indicator.

We recently received a Globus from a collector and opened it up for repair and reverse engineering. Although the Globus does all its calculations mechanically, it has some electronics to control the motors. Inconveniently, all the wires in the wiring harness to the external connector had been cut so I had to do some reverse engineering before we could power it up. In this blog post, I explain how the electronics operate. (For an overview of the mechanical components inside the Globus, see my previous article.)

A closeup of the gears inside the Globus. It performed calculations with gears, cams, and differentials.

Functionality

The primary purpose of the Globus is to indicate the spacecraft's position. The globe rotated while fixed crosshairs on the plastic dome indicated the spacecraft's position. Thus, the globe matched the cosmonauts' view of the Earth, allowing them to confirm their location. Latitude and longitude dials next to the globe provided a numerical indication of location. The light/shadow dial at the bottom showed when the spacecraft would be illuminated by the sun or in shadow.

The mode of the Globus is controlled by a three-position rotary switch near the top of the Globus. The middle position "З" (Земля, Earth) shows the position of the spacecraft over the Earth. The left position, "МП" (место посадки, landing site) selects the landing position mode. The third position "Откл" (off) turns off most of the Globus. This rotary switch is surprisingly complicated with three wafers, each with two poles. Most of the electronics go through this switch, so this switch will appear often in the schematics below.

The rotary switch to select the landing angle mode.

In the landing position mode, the Globus rotates to show where the spacecraft would land if you fired the retrorockets now. This allowed the cosmonauts to evaluate the suitability of this landing site. This position is computed simply by rapidly rotating the globe through a fraction of an orbit, since the landing position will be on the current orbital track. Most of the electronics in the Globus control the motor that performs this rotation.

Overview of the electronics

The Globus is primarily mechanical, but it has more electrical and electronic components than you might expect. The mechanical motion is powered by two solenoids with ratchets to turn gears. The landing site mode is implemented with a motor to rotate to the landing position, controlled by two limit switches. An electroluminescent light indicates the landing position mode. A potentiometer provides position feedback to external devices.

To control these components, the Globus has an electronics board with four relays, along with a germanium power transistor and some resistors and diodes.2 Bundles of thin white wires with careful lacing connect the electronics board to the other components.

The electronics circuit board.

The back of the circuit board has a few more diodes. The wiring is all point-to-point; it is not a printed-circuit board. I will explain the circuitry in more detail below.

The back of the circuit board.

The drive solenoids

The green cylinder at the front is the upper solenoid, driving the orbital motion. The digit wheels to indicate orbital time are at the left.

The Globus contains two ratchet solenoids: one for the orbital rotation and one for the Earth's rotation. The complex gear trains and the motion of the globe are driven by these solenoids. These solenoids take 1-hertz pules of 27 volts and 100ms duration. Each pulse causes the solenoid to advance the gear by one tooth; a pawl keeps the gear from slipping back. These small rotations drive the gears throughout the Globus and result in a tiny movement of the globe.

The lower driving solenoid powers the Earth rotation.

As the schematic shows, the solenoids are controlled by two switches that are closed in the МП (landing position) and З (Earth orbit) modes. The solenoids are powered through three pins. The wiring doesn't entirely make sense to me. If powered through pins 2A and 7A, the Earth motor is switched while the orbit motor is always powered. But if powered through pins 2A and 5B, both motors are switched. Maybe pin 7A monitors the on/off status of the Globus.

Schematic diagram of the solenoid wiring.

By powering the solenoids with 1 hertz pulses, we caused the Globus to rotate. The motion is very slow (90 minutes for an orbit and one day for the Earth's rotation), so we tried overclocking it at 10 hertz. This made the motion barely visible; Marc used a time-lapse to speed it up in the video below.

The landing location mechanism

The Globus can display where the spacecraft would land if you started a re-entry burn now, with an accuracy of 150 km. This is computed by projecting the current orbit forward for a particular distance, specified as an angle. The cosmonaut specifies this value with the landing angle knob (details). Rotating the globe to this new position is harder than you might expect, using a motor, limit switches, and the majority of the electronics in the Globus.

The landing angle control.

The landing angle knob pivots the angle limit switch, shown below. The swing arm moves as the globe rotates to the landing position and hits the angle limit switch when the landing position is reached. When returning to Earth orbit mode, the swing arm swings back until it hits the fixed limit switch. Thus, the globe is rotated by the selected amount when displaying the landing position.

The landing angle function uses a complex mechanism.

To control the motor, the rotary switch reverses the DC motor based on the mode, while the limit switches and power transistor turn the motor on and off. In landing position mode (МП), the motor spins the globe forward. The mode switch controls the direction of current flow: from upper right, through the motor, through the angle limit switch, through the transistor, and to ground at the bottom. The motor will rotate the globe and the arm until it hits the "landing position" limit switch, cutting power to the motor and activating the path to the light circuit, which I will discuss below. The diode prevents current flowing backward through the motor to the relay. The power transistor apparently acts as a current sink, regulating the current through the motor.

Schematic diagram of the landing location mechanism.

In Earth orbit mode (З), the motor spins the globe back to its regular position. The mode switch reverses the current flow through the motor: from the upper-left, through the diode and the motor, and out the lower-right to the transistor. At the bottom, the relay completes the circuit until the moving arm hits the fixed orbit limit switch. This opens the normally-closed contact, cutting power to the relay, opening the relay contact, and stopping the motor.

The landing place light

The upper-left corner of the Globus has an electroluminescent light labeled "Место посадки" (Landing place). This light illuminates when the globe indicates the landing place rather than the orbital position. The light is powered by AC provided on two external pins and is controlled by two relays. One relay is activated by the landing circuit described above, when the limit switch closes. The second relay is driven by an external pin. I don't know if this is for a "lamp test" or control from an external system.

Schematic diagram of the circuitry that controls the electroluminescent light.

We powered the light with an EL inverter from Adafruit, which produces 100 VAC at 2KHz, perhaps. The spacecraft used a "Static Inverter" to power the light, but I don't have any details on it. The display provides a nice blue glow.

The landing position indicator, illuminated.

The potentiometer

A 360° potentiometer (below) converts the spacecraft's orbital position into a resistance. Sources indicate that the Globus provides this signal to other units on the spacecraft, but I don't know specifically what these devices are. The potentiometer appears to linearly track the spacecraft's position through the orbital cycle. Note that this is not the same as the latitude, which oscillates, or the longitude, which is non-linear.

The potentiometer converts the orbital position into a voltage. To the right is the cam that produces the longitude display. Antarctica is visible on the globe.

As the schematic below shows, the potentiometer has a resistor on one leg for some reason.

Schematic diagram of the orbital-position potentiometer.

The external connector

To connect the Globus to the rest of the spacecraft, the back of the Globus has a 32-pin connector, a standard RS32TV Soviet military design.

The back of the Globus, with the connector at the upper left.

The connector was wired to nearby 5-pin and 7-pin terminal strips. In the schematics, I label these connectors as "B" and "A" respectively. Inconveniently, all the wires to the box's external connector were cut (the black wires), perhaps to decommission the unit. The pinout of the external connector is unknown so we can't easily reconnect the wires.

A closeup of the back of the connector showing the cut black wires.

Conclusions

By tracing out the wiring of the Globus, I determined its circuitry. This was more difficult than expected, since the wiring consists of bundles of identical white wires. Moreover, many things go through the mode switch, and its terminals were inaccessible. Between the mode switch and the limit switches, there were many cases to check.

Once I determined the circuitry, we could power up the Globus. So far, we have powered the solenoids to turn the Globus. We also illuminated the landing position light. Finally, we ran the landing position motor.

Follow me on Twitter @kenshirriff or RSS for updates. I've also started experimenting with Mastodon recently as @oldbytes.space@kenshirriff. Many thanks to Marcel for providing the Globus.

Notes and references

1. In Russian, the name for the device is "Индикатор Навигационный Космический" abbreviated as ИНК (INK). This translates to "space navigation indicator." ↩

2. Most of the diodes are flyback diodes, two diodes in series across each relay coil to eliminate the inductive kick when the coil is disconnected. ↩