Reverse engineering circuitry in a Spacelab computer from 1980

Spacelab was a reusable laboratory that could be carried in the cargo bay of the Space Shuttle, providing lab space for astronauts and experiments. Spacelab was controlled by a French-built minicomputer, called the Mitra 125 MS. Unlike modern computers, this computer didn't contain a microprocessor chip. Instead, its 16-bit processor was constructed from several boards of chips. In this article, I reverse-engineer one of the processor boards, shown below, part of the computer's Arithmetic/Logic Unit (ALU). The Mitra 125 MS computer, built by CIMSA, with one of the ALU/register cards shown. Spacelab consisted of a pressurized cylindrical laboratory that held experiments, computers, and work areas for researchers. A tunnel connected the laboratory to the Shuttle, allowing researchers to move between the Shuttle and Spacelab. Spacelab also supported up to five unpressurized "pallets" that were exposed to space, holding experiments such as telescopes and sensors. The illustration below…