D-17B

The D-17B computer was used in the Minuteman I NS-1OQ missile guidance system. The complete guidance system contained a D-17B computer, the associated stable platform, and power supplies.

The D-17B weighed approximately 62 pounds (28 kg), contained 1,521 transistors, 6,282 diodes, 1,116 capacitors, and 504 resistors. These components were mounted on double copper-clad, engraved, gold-plated, glass fiber laminate circuit boards. There were 75 of these circuit boards and each one was coated with a flexible polyurethane compound for moisture and vibration protection. The high degree of reliability and ruggedness of the computer were driven by the strict requirements of the weapons system.

High reliability was required of the D-17B. It controlled a key weapon that would have just one chance to execute its mission. Reliability of the D-17B was achieved through the use of solid-state electronics and a relatively simple design. Simpler DRL (diode-resistor) logic was used extensively, but less-reliable DTL (diode-transistor) logic was used only where needed. In the late 1950s and early 1960s, when the D-17B was designed, transistors lacked today's reliability. DTL provided, however, either gain or inversion. Reliability was also enhanced by the rotating disk memory with non-destructive readout (NDRO). In actual real-time situations, Minuteman missiles achieved a mean time between failure (MTBF) of over 5.5 years.

The Soviets had much larger rockets and could use vacuum tubes (thermionic valves) in their guidance systems. (The weights of the Minuteman I and II remain classified, but the Minuteman III was 35,000 kg versus the Soviet R-7 missile (1959) of 280,000 kg.) The US planners had to choose either to develop solid state guidance systems (which weigh less) or consider the additional cost and time delay of developing larger rockets.

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