The Missing Overbar That Sank Mariner 1 and Redefined Software QA

In July 1962, a single missing overbar in the Mariner 1 guidance code caused it to misinterpret raw radar data as real course deviations, leading to destructive corrections and the mission’s destruction 293 seconds after liftoff (costing about $18.5 million then, ~$190 million today). Arthur C. Clarke later dubbed it the most expensive hyphen in history. A separate hardware fault also contributed, but the episode spurred rigorous code review, equation-to-code verification, and formal testing practices that shaped software engineering for space missions; Mariner 2, launched five weeks later, successfully reached Venus and provided crucial data. The event remains a cautionary tale about the gap between paper mathematics and executable code.