The D-37C (D37C) is the computer component of the all-inertial NS-17 Missile Guidance Set (MGS) for accurately navigating to its target thousands of miles away. The NS-17 MGS was used in the Minuteman II (LGM-30F) ICBM. The MGS, originally designed and produced by the Autonetics Division of North American Aviation, could store multiple preprogrammed targets in its internal memory.
Unlike other methods of navigation, inertial guidance does not rely on observations of land positions or the stars, radio or radar signals, or any other information from outside the vehicle. Instead, the inertial navigator provides the guidance information using gyroscopes that indicate direction and accelerometers that measure changes in speed and direction. A computer then uses this information to calculate the vehicle's position and guide it on its course. Enemies could not "jam" the system with false or confusing information.
The Ogden Air Logistics Center at Hill AFB has been Program Manager for the Minuteman ICBM family since January 1959. The base has had complete logistics management responsibilities for Minuteman and the rest of the ICBM fleet since July 1965.
The D-37C computer consists of four main sections: the memory, the central processing unit (CPU), and the input and output units. These sections are enclosed in one case. The memory is a two-sided, fixed-head disk which rotatesat 6000 rpm. It contains 7222 words of 27 bits. Each word contains 24 data bits and three spacer bits not available to the programmer. The memory is arranged in 56 channels of 128 words each plus ten rapid access channels of one to sixteen words. The memory also includes the accumulators and instruction register.
The MM II missile was deployed with a D-37C disk computer. Autonetics also programmed functional simulators for flight program development and testing, and the code inserter verifier that was used at Wing headquarters to generate the codes to go into the airborne computer. It became necessary to verify not only that the flight program software was correct, but there was no code that would lead toward an unauthorized or accidental launch. TRW, Inc. continued its role of independent verification that first called verification and validation and then became nuclear safety cross check analysis (NSCCA). Logicon RDA was selected to perform the NSCCA of the targeting and execution plan programs developed by TRW.[1]
When MM III was developed, Autonetics generated the guidance equations that were programmed into the D37D computer, which contained a hybrid explicit guidance system for the first time. A new class of program was required by the Joint Strategic Targeting Planning Staff to select targets for the multiple warhead system. The Missile Application Programs were developed for these functions.
The next major update to the operational software was made under the Guidance Replacement Program. Autonetics (later acquired by The Boeing Co.) developed the necessary software for the new flight computer.
This section was excerpted from the original document, "Minuteman" D-37C Digital Computer System Depot Overhaul. Autonetics, Division of North American Rockwell, Inc. Anaheim, California. FET-D-120-D37/4.
The control unit interprets and processes all machine functions and consists of a location counter, the instruction register, and the phase register.
The arithmetic unit consists of three registers: the accumulator (A), lower accumulator (L), and the number register (N). Only the A and L registers are addressable.
The D-37C computer memory consists of a rotating magnetic disk driven by a synchronous motor at 6000 rpm. Adjacent to the disk are two fixed head plates which house the read and write heads. The disk has a thin magnetic oxide coating on both sides for storing information. This disk is supported by air bearings generated by the rotating disk. The disk is divided into tracks or channels of 128 words each for main memory. A total capacity of 7222 words may be contained in the 56 channels of 128 Sectors, six 4-word loops, one 8-word loop, one 16-word loop and six 1-word loops.
The computer uses a full 24-bit instruction word and data word. Data is represented in one of two fashions, as a 23-bit binary fraction (full word) or as a 10-bit fraction (split word). The two formats are shown in the figure. Instructions also have two formats, either flagged or unflagged as indicated in the figure. A list with all of the available instructions with numeric and mnemonic codes follows. For more information on programming see:
Kee, W. T. Programming Manual for the D-37C Computer. Anaheim, California, Autonetics, Division of North American Rockwell, Inc., 30 January 1965.
| MNEMONIC CODE | DESCRIPTION | NUMERIC CODE | CHANNEL (C), SECTOR (S) | |
|---|---|---|---|---|
| ADD | Add | 64 | C, S | |
| ALC | Accumulator Left Cycle | 00 | 26, S | |
| ANA | AND to Accumulator | 40 | 42, S | |
| ARC | Accumulator Right Cycle | 0 | 36, S | |
| ARS | Accumulator Right Shift | 0 | 32, S | |
| AWC | Add Without Carry | 40 | 50, S | |
| CLA | Clear And Add | 44 | C, S | |
| COA | Character Output A | 0 | (40-76), S | |
| CoM | Complement | 40 | 46, S | |
| DIA | Discrete Input A | 40 | 02, S | |
| DIB | Discrete Input B | 40 | 00, S | |
| DIC | Discrete Input C | 40 | 20, S | |
| DIV | Divide | 34 | C, S | |
| DOA | Discrete Output A | 40 | 54, XX2 | |
| DOB | Discrete Output B | 40 | 54, XX1 | |
| DPP | Disable Platform Power | 40 | 62, X20 | |
| ECO | Enable Cable Output | 40 | 62, X02 | |
| ECI | Enable Cable Input | 40 | 62, X03 | |
| EFC | Enable Fine Countdown | 40 | 26, S | |
| EPP | Enable Platform Power | 40 | 62, X40 | |
| FCL | Full Compare and Limit | 14 | C, S | |
| GBP | Generate Bit Pattern | 40 | 64, S | |
| GPT | Generate Parity Bit | 40 | 60, S | |
| HFC | Halt Fine Countdown | 40 | 24, S | |
| HPR | Halt and Proceed | 40 | 22, S | |
| LPR | Load Phase Register | 40 | (70-76), S | |
| MAL | Modify A and L | 40 | 52, S | |
| MIM | Minus Magnitude | 40 | 44, S | |
| MPY | Multiply | 24 | C, S | |
| ORA | OR to Accumulator | 40 | 40, S | |
| PLM | Plus Magnitude | 40 | 56, S | |
| RIC | Radio Intercommunication | 0 | 24, 001 | |
| RSD | Reset Detector | 40 | 62, X10 | |
| SAD | Split Add | 60 | C, S | |
| SAL | Split Accumulator Left Shift | 0 | 20, S | |
| SAR | Split Accumulator Right Shift | 0 | 30, S | |
| SCL | Split Compare and Limit | 4 | C, S | |
| SMP | Split Multiply | 20 | C, S | |
| SPM | Split Plus Magnitude | 40 | 66, S | |
| SRD | Simulate Transient | 0 | 16, S | |
| SSU | Split Subtract | 70 | C, S | |
| STO | Store Accumulator | 51 | C, S | |
| SUB | Subtract | 74 | C, S | |
| TMI | Transfer on Minus | 30 | C, S | |
| TRA | Transfer | 50 | C, S | |
| TSM | Transfer Sector on Minus | 40 | 06, S | |
| TSZ | Transfer Sector on Zero | 40 | 04, S | |
| TZE | Transfer on Zero | 10 | C, S | |
| VIA | Voltage Input A | 40 | 10, S | |
| VIB | Voltage Input B | 40 | 12, S | |
| VIC | Voltage Input C | 40 | 14, S | |
| VID | Voltage Input D | 40 | 16, S | |
| VIE | Voltage Input E | 40 | 30, S | |
| VIF | Voltage Input F | 40 | 32, S | |
| VIG | Voltage Input G | 40 | 34, S | |
| VIH | Voltage Input H | 40 | 36, S |
Both the D-17B and the D-37C computers were designed and built by Autonetics, then a division of North American Aviation, later a division of Boeing, for the real time guidance and control of a Minuteman ICBM from launch to detonation. The D-17B is a component of the NS-10Q missile guidance system for the Minuteman I, while the D-37C is a component of the NS-17 missile guidance system for the Minuteman II. There are many basic similarities between the two designs. They are both synchronous, serial machines with fixed head disks for primary memory. They have two-address instructions, half and whole word precision, and many similar instruction operator codes. The differences in the two computers are based mainly upon their differing technologies. The D-17B was built in 1962 using primarily diode-resistor logic and diode-transistor logic as needed to realize its logic circuits. On the other hand, the D-37C was built in 1964[1] using small scale integrated circuits made by Texas Instruments with discrete components only in the internal power supplies.
| + Comparison of D-17B and D-37C | |||
| Model: | D-17B | D-37C | |
|---|---|---|---|
| Year: | 1962 | 1964 | |
| Type: | Serial, Synchronous | ||
| Number System: | Binary, fixed point, 2's complement | ||
| Data Word Length: | 11 or 24 bit (double-precision) | ||
| Instruction Word Length: | 24 bit | ||
| Number of Instructions: | 39 | 57 | |
| Execution Times: | |||
| Add | 78 1/8 microsec | Same | |
| Multiply | 1 millisec | Same | |
| Divide | (software) | 2 msec | |
| Clock Channel: | 345.6 kHz | Same | |
| Addressing: | Direct of entire memory | Direct within Bank (1/4 of memory) | |
| Memory: | |||
| Word Length | 24 bits plus 3 timing | Same | |
| Type | Ferrous oxide-coated NDRO disc | ||
| Cycle Time | 78 1/8 microsec minimal | " | |
| Capacity | 5,454 or 2,727 words (double precision) | 14,444 or 7,222 words | |
| Input/Output: | |||
| Input Lines | 48 digital | 65 digital 32 analog | |
| Output Lines | 28 digital 12 analog 3 pulse | 45 digital 16 analog 8 pulse | |
| Program | 800 5-bit characters/sec | Same | |
| Physical Characteristics: | |||
| Dimensions | 20" high, 29" diameter | 20.9 × 6.9 × 9.5" | |
| Power | 28 VDC ±1 V at 19 A | 28 VDC ±1.7 V at 15 A | |
| Circuits: | Discrete DRL and DTL | IC DRL and DTL | |
| Software: | Minimal delay coding machine language modular special-purpose subroutines | ||
| Reliability: | 5.5 years MTBF | (classified) | |
APPLICATIONS Missile guidance and control
PROGRAMMING AND NUMERICAL SYSTEM Internal number system: Binary Binary digits/word: 27 Arithmetic system: Fixed point
ARITHMETIC UNIT Excl. Stor. Access MicrosecAdd 78Mult 1,016Div 2,030Arithmetic mode: SerialTiming: SynchronousOperation: Sequential
STORAGE No. of AccessMedium Words MicrosecDisk 6,912 5,000 (Avg) (General Purpose Channels)Disk 29 (Rapid Access Loops) 40 (1 word loop) 160 (4 word loop) 320 (8 word loop) 640 (16 word loop)
POWER, SPACE, WEIGHT, AND SITE PREPARATION Power, computer 0.169 kW Volume, computer 0.40 cu ft Weight, computer 26 lbs
Jerrold Foutz, President, SMPS Technology was the responsible engineer for the Minuteman D-37B guidance and control computer power supply study program which defined the state-of-art techniques later used in one of the first integrated-circuit military computers. These techniques included high-speed flat-pack power transistors and diodes (the first silicon power devices that could switch at 20 kHz and higher), high frequency DC-to-DC converters (100 kHz reduced to 20 kHz for reliability safety margins), high frequency pulse-width-modulated power supplies (20 kHz), metal substrate multilayer circuit boards (removing eight watts per cubic inch in space environment with 40°C rise, junction to system heat sink), and radiation circumvention techniques that removed all electrical power from the power distribution system, including decoupling capacitors, in less than 1 microsecond and restored to the specified voltage in a few microseconds upon command. Responsible for developing these concepts from exploratory development through to the production design. The basic power supply configuration was maintained in later Minuteman missiles whereas other components underwent major redesigns. Also developed, but not used, was a complete liquid dielectric cooling system based on phase change. This study verified, for the first time, that such a system could work in zero-gravity, and that the liquid dielectric showed no compatibility problems with the chosen electronic components over a test period lasting eight years.