Mariner 1 was the first spacecraft of the Mariner program. Intended to fly by Venus, it was destroyed by range safety during its launch on July 22, 1962. A hardware failure in an antenna caused the booster to lose contact with guidance systems on the ground, so an onboard computer assumed control. However, that computer's software contained a bug.

Reports that the bug consisted of a missing comma (specifically "DO I=1.10" instead of "DO I=1,10") are now considered to be an urban legend; the failure is blamed on a transcriber missing the handwritten superscript bar in "R-dot-bar sub n" (the n-th smoothed value of derivative of radius). Without the smoothing function indicated by the bar, normal minor variations of velocity were treated as if they were serious.

Its mission was later completed by Mariner 2.