A Block II Apollo Command Module Inertial Measurement Unit (IMU) which comprised the heart of the spacecraft’s primary guidance and navigational control system (PGNCS). The device is spherical and approximately 12″ in diameter, and bears a metal NASA tag reading: “Apollo G. &. N. System. Name: Inertial Measuring Unit, Part No. 2018601-241, Serial No. AC 39, Cont. No. NAS 9-497.” Above this is another tag, labeled “PIP,” reading: “X: 2AP-293R, Y: 3AP-313, Z: 2AP-241.” In fine condition with expected wear, including various marks and scratches. The IMU provided inertial reference inputs to the onboard Apollo Guidance Computer, and Flight Direction Attitude Indicators and served as a fixed reference point in space with which to measure vehicle displacement. Encased within the housing are three inertial rate integrating gyros and three pulsed-integrating pendulous accelerometers; these are mounted to a gimbaled platform to allow three directions of freedom. Any displacement of the platform, resulting from either a change in spacecraft attitude or velocity, would be sensed and communicate signals representative of the magnitude and direction of displacement. The IMU was developed by Dr. Charles Draper and the MIT Instrumentation Laboratory and manufactured by General Motors (A.C. Spark Plug Division). The technology is a derivative of the Polaris Ballistic Missile submarine guidance system. An extreme rarity, auction records indicate this is likely the first of its kind offered for sale.
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