I stumbled upon this interesting fact about the Mariner 1 spacecraft while browsing Wikipedia today (I was researching about loops in programming):
The Fortran DO loop caused an orbit computation error in a Mercury flight, and was long suspected to have caused the crash of the Mariner 1 space rocket on 22 July 1962 .
According to the NASA site, it was actually an omitted hyphen in the spacecraft's program that actually did Mariner 1 in.
Mariner 1 was supposed to explore Venus but was destroyed shortly after takeoff. Its backup, Mariner 2, was successfully launched however.