Mars 4, Soviet probe, launched 1973

The Soviets launched the Mars 4 probe on July 21, 1973 to orbit the Red Planet.  Shortly before it reached Mars, two of its on-board computers failed and it passed within 2000km of the Martian surface on February 10, 1974.  It did send back some information,  but little of it was useful.

Mars 5, Soviet probe, launched in 1973

The Mars 5 spacecraft was launched by the Soviet Union, July 25, 1973.  It was launched just 4 days after its twin, Mars 4.  However, unlike Mars 4, Mars 5 was considered a success.  Mars 4 was supposed to Mars but its retro-rockets failed to fire so it could settle into orbit.  It took pictures and made some measurements on its flyby.

Mars 5 performed almost perfectly.  It reached Mars on February 12, 1974 and obtained an elliptical orbit.  It made 22 revolutions of the planet before the transmitter housing depressurized and ended the mission.

Here are some of the 60 images that successfully transmitted.