In 1973, the USSR launched Mars 4, 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 4 reached Mars on 10 Feb 1974. Its intended mission was to be an orbiting station. Sadly, retro-rockets failed to fire, due to a flawed computer chip, and it flew past within only 2200-km of the planet. A limited series of pictures and data were returned, including the first detection of the nightside ionosphere. Equipment on board for its intended mission included instruments to detect atmospheric hydrogen, carbon dioxide, ozone, water, magnetic field and surface temperature. The craft remained in solar orbit, and transmitted interplanetary data back to Earth.« The Scientific Exploration of Mars, by Fredric W. Taylor. - book suggestion.