Mars/Venus 3MV series, 1963-1972

As with the first campaign to Mars and Venus in 1960-61, the second campaign to both planets in 1962 failed. Of the ten spacecraft launched, only two survived launch and neither of those completed its cruise in a functioning state. But the long Highi of Mars 1 was very encouraging, and the 2M V design was upgraded with new avionics to make the 3MV spacecraft for the 1964 launch opportunities to Venus and Mars.

Six 3MV launches were planned for the 1964 campaign, three each for Mars and Venus, but only five came off. In view of the high rate of previous failures, the first launch in each set of three was to test the 3MV/launeh vehicle system. However, both the Mars vehicle test flight in November 1963 and the Venus vehicle test flight in February 1964 were lost to launch vehicle failures. Although there was little time left before the launch window to Venus opened in March 1964, it proved possible to launch the two spacecraft in late March and early April. The first mission was lost to a launch vehicle failure, and the second, designated Zond 1, failed 2 months into the cruise when pressurization was lost. A single 3MV was successfully launched to Mars in November 1964. Designated Zond 2, it failed in transit after 1 month, in this case because of avionics problems. Both of these missions were given the designation wZond’ because it was realized shortly after launch that neither would be able reach its target in a functioning state.

The 3MV spacecraft that missed its Mars launch window in November 1964 was launched as a test spacecraft in July 1965. It conducted a successful flyby of the Moon as Zond 3, but failed its planetary test objectives when communications were lost before reaching Mars distance. It was the last 3MV launched to Mars. Later in November 1965 three more were launched to Venus. The first, Venera 2, was lost only 17 days before Venus encounter and the second, Venera 3, was lost just as the spacecraft approached the planet. However, they w7ere both the first Soviet planetary missions to reach the vicinity of their targets. The third spacecraft was lost to a launch vehicle failure.

By March 1966 the Soviet planetary program had no success to show for nineteen launch attempts, eleven to Venus and eight to Mars, since the start of the program in October 1960. Meanwhile, the US had achieved successful flyby missions of Venus in 1962 and Mars in 1965. Also, the builder of all Soviet robotic spacecraft to date, OKB-1, was overloaded with work on the manned space program and so the robotic program was transferred to NPO-Lavochkin. Throughout 1966 Lavochkin modified Korolev’s designs to deal with the problems revealed by previous flights, and began to produce their own versions of the Ye-6 and Ye-8 lunar spacecraft and the 3MV planetary spacecraft for Venus. It was decided not to attempt further ЗМ V missions to Mars, and instead to design a new’ heavier spacecraft w’hich would enter into orbit around the planet and deliver a soft lander. This strategy was intended to upstage the US flyby missions of Venus and Mars scheduled for the 1967-1969 launch window’s with entry probe and lander missions to Venus and with orbiter and lander missions to Mars.

Lavochkin prepared two new’ 3MV spacecraft with entry probes for the Venus 1967 opportunity. The entry probe was designed to make atmospheric measurements while descending by parachute and to survive impact on the surface for an assumed marginal atmospheric pressure. Both were launched in June 1967. The second w as lost to a launch vehicle failure, but on October 18, 1967 the first. Venera 4, became

the first successful planetary entry probe. The Soviets initially believed that it had survived all the way to the surface, but it transpired that it had been overwhelmed by conditions while still high in the atmosphere.

This strategy of two Venus probe launches at each opportunity was repeated for the next three Venus launch opportunities in 1969, 1970 and 1972. There were four successes in six launches, Venera 5 and 6 in 1969, Venera 7 in 1970, and Venera 8 in 1972. The probes were strengthened for each opportunity until they were finally able to survive the high pressures and temperatures at the surface of Venus. The first spacecraft to land and survive on the surface of another planet was Venera 7. Venera 8 duplicated the feat in 1972 near the morning terminator on the illuminated side of Venus and with a more versatile set of measurements.