In 1973, the USSR launched the Mars 7, on a Proton SL-12/D-1-e booster. It was one of several Soviet Mars probes - Mars 4, 5, 6, and 7 - launched in Jul-Aug 1973. The Mars 7 spacecraft was made up of a flyby bus and a descent module intended separate to study the atmosphere and land on the Martian surface with instruments to study soil composition, and mechanical properties soil sensors. The combined vehicle reached Mars on 9 Mar 1974. However, an equipment problem believed to be due to a faulty computer chip resulted in the premature separation of the lander. Being released about 4 hours too early, the lander missed the planet by 1300-km. Both the bus and the lander instead travelled into solar orbits.« The Scientific Exploration of Mars, by Fredric W. Taylor. - book suggestion.