The Mars program was a series of uncrewed spacecraft launched by the Soviet Union between 1960 and 1973. The spacecraft were intended to explore Mars, and included flyby probes, landers and orbiters. Early Mars spacecraft were small, and launched by Molniya rockets. Starting with two failures in 1969, the heavier Proton-K rocket was used to launch larger 5 tonne spacecraft, consisting of an orbiter and a lander to Mars. The orbiter bus design was likely somewhat rushed into service and immature, considering that it performed very unreliably in the Venera variant after 1975. This reliability problem was common to much Soviet space hardware from the late 1960s and early 1970s and was largely corrected with a deliberate policy, implemented in the mid-1970s, of consolidating (or "debugging") existing designs rather than introducing new ones. The names of the "Mars" missions do not need to be translated, as the word "Mars" is spelled and pronounced approximately the same way in English and Russian. In addition to the Mars program, the Soviet Union also sent a probe to Mars as part of the Zond program; Zond 2, however it failed en route. Two more spacecraft were sent during the Phobos program; both failed. In 1996, Russia launched Mars 96, its first interplanetary mission since the dissolution of the Soviet Union, however it failed to depart Earth orbit. Spacecraft Mars 1M The first Soviet attempts to send a probe to Mars were the two Mars 1M spacecraft, which each had a mass of about 650 kg. Both were launched in 1960 and failed to achieve orbit. The spacecraft were dubbed Marsnik by the Western media. Mars 2MV Mars 1 was launched in 1962 but failed en route to Mars. Two other Soviet launches at around the same time, Mars 2MV-4 No.1 and Mars 2MV-3 No.1 were spacecraft, however both failed to leave Earth orbit due to problems with the upper stages of their carrier rockets. Mars 2M Mars 2M No.521 and Mars 2M No.522, known in the West as Mars 1969A and B, were heavier spacecraft with masses of . They were launched by Proton-K rockets, and consisted of orbiters. Both were destroyed during launch. Mars 4M The Mars 4M spacecraft; Mars 2 and Mars 3 missions consisted of identical spacecraft, each with an orbiter and an attached lander, which became the first spacecraft to reach the surface of Mars. The orbiters' primary scientific