Apollo Lunar Module Inertial Measurement Unit (IMU) — G&N Gyro Ball

With nested rotating spheres within spheres, this mechanical device afforded motion sensing on 2 axis, much less effectively that the 6-axis accelerometers now standard in all of our cell phones (and built on-chip with Silicon MEMS). But she is a beauty inside, and the subject of a Pilat painting (details in comment below).

UPDATE: new research shows that this S/N 39, was in 1973 a LM spare located at AC/Delco in Milwaukee. Two of the three Inertial Reference Integrating Gyroscopes (IRIG) were prime spares for Apollo 17.

This Block II Apollo Inertial Measurement Unit (IMU) comprised the heart of the spacecraft’s primary guidance and navigational control system (PGNCS). Here is a cool 1-minute video on this “ball of wizardry and magic”..

The IMU provided inertial reference inputs to the onboard Apollo Guidance Computer, and Flight Director 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. RRAuction described it as “an extreme rarity, auction records indicate this is likely the first of its kind offered for sale.”

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.” An artifact in the Future Ventures’ 🚀 Space Collection.