Twenty-five years ago today — July 7, 1988 — the Soviet Union launched a Proton-K from the Baikonur Cosmodrome carrying the Phobos 1 spacecraft.
(Phobos 1. Image from the National Space Science Data Center.)
Phobos 1, launched just a few days before its twin Phobos 2, was built to study the composition of its namesake Martian moon, and also to study the Martian atmosphere and surface by remote sensing from orbit. It also carried instruments to study the Sun and the interplanetary space environment.
The spacecraft operated well until an attitude system failure — caused by faulty software — oriented Phobos 1 away from the Sun and prevented its solar arrays from recharging its batteries. The failure occurred sometime between August 30 and September 2, 1988,* and as a result Phobos 1 never reached Mars.
*As of the posting date, the NSSDC page records this failure as happening in 1989; however, other sources (e.g., this page) give the date as 1988, when the spacecraft was on the way to Mars.