Spacelab, the European laboratory module for Space Shuttle missions, relied on a French-built Mitra 125 MS minicomputer rather than modern microprocessors. Unlike today's computers, this 16-bit system was constructed from multiple boards of discrete TTL chips. The computer served as mission control for experiments, with three units providing redundancy for critical operations in space.

The computer's arithmetic operations were handled by a custom-built ALU using eight 74181 ALU chips. These chips, manufactured by Texas Instruments, contained about 170 transistors each and performed basic arithmetic and logical operations. The implementation spread across three boards with numerous additional chips including multiplexers and registers to create a functional processing unit.

The surprising 32-bit ALU design likely improved performance for multiplication and floating-point operations in this 16-bit computer. The chips were chained together with carry-lookahead circuits to speed up calculations. This reverse engineering project reveals the ingenuity of early space computing when every transistor counted and reliability was more important than processing power.