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D-17B
The D-17B was the computer used 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 , 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.
==Design constraints==
Since an airborne, computer-controlled missile only gets one chance to execute its mission, the design specifications of the D-17B required very high reliability. This was achieved by using DRL (diode-resistor) logic extensively and only using DTL (diode-transistor) logic where gain or inversion was required in this fully solid-state computer. In the early 1960s when the D-17B was designed, transistors were not as reliable as they are now, thus the designers used transistors only when necessary. The rotating disk memory, with non-destructive readout (NDRO), also enhanced the reliability of the computer. In actual, real-time situations involving Minuteman missiles, the mean time between failures (MTBF) was 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 are 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 between developing solid state guidance systems and the considerable cost and time delay of developing larger rockets. Most would now agree that the correct decision was made.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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