Mariner 1, America's first Venus probe, was destroyed over a guidance-code error

Mariner 1 was the first spacecraft of NASA's Mariner program, intended to be the first American probe to fly by Venus. It launched on an Atlas-Agena rocket from Cape Canaveral on July 22, 1962. Within minutes, the rocket began to veer off course, and the range safety officer sent the command to destroy it before it could threaten anyone on the ground. The mission was lost less than five minutes after liftoff.

The investigation traced the failure to the guidance system. The rocket's flight path was controlled by equations that had been written out by hand in a specification and then transcribed into the computer program. In that transcription, an error crept in — a symbol was dropped or mis-copied — so the guidance software mishandled the rocket's motion and steered it wrong. Popular retellings, helped along by Arthur C. Clarke, turned it into 'the most expensive hyphen in history,' though the technical reality was a missing smoothing term in the hand-copied equations rather than a literal hyphen.

The loss cost on the order of $18 million and a launch window, but its sibling spacecraft, Mariner 2, launched successfully a few weeks later and became the first probe to fly by another planet. Mariner 1 became a foundational cautionary tale in software engineering: a reminder that a single transcription error, in code that controls something expensive and unforgiving, can be catastrophic — and that the humble act of copying a formula by hand deserves as much checking as the formula itself.