Landing on the Moon, Venus, and Mars

TIMELINE: AUG 1970-FEB 1972

The Soviets reached the zenith of their success at the Moon with robotic missions in 1970 and 1971. In September 1970 the Luna 16 mission successfully returned a sample of the Moon to Earth; an impressive achievement still unmatched by the US. In November the Luna 17 mission successfully deployed the first robotic rover on the Moon, Lunokhod 1; another achievement unmatched by the US. An attempt at sample return in September 1971 failed when communications were lost as Luna 18 was landing. It was followed immediately by Luna 19, a successful orbiter version of the spacecraft. Luna 20 became the second successful sample return mission in February 1972.

The Soviets also finally achieved a landing on Venus after eleven attempts since February 1961. Venera 7 was launched on August 17, 1970. with a descent capsule modified to withstand the massive surface pressure on Venus, and this succeeded in descending through the entire atmosphere and gently impacting the surface where it continued to operate for 23 minutes before succumbing to the high temperature. The Soviets finally had some success at Mars in 1971 after eight attempts since October 1960. The 1971 opportunity was not as energetically favorable as in 1969. requiring the landers to be released in the approach rather than after entering orbit around the planet. This and several engineering problems with the Mars-69 spacecraft forced a complete redesign. The 1971 Mars spacecraft became the basic design reference for all Soviet Proton-launched planetary spacecraft thereafter.

The Soviet plan in 1971 was to start with an orbiter to Mars which would provide precise information on the position of the planet to the spacecraft that followed, to enable these to deploy their landers on the necessarily very precise entry trajectories before themselves entering into orbit. This plan tvas foiled when the launch of the leading orbiter failed on May 10. Fortunately, the Soviets had a backup plan in which the approaching carrier spacecraft would use on board optical navigation to determine the position of Mars and autonomously update their navigation system so that they could properly deploy their landers. This complex and sophisticated system was far in advance of its lime, but very risky. The Mars 2 syslem rvorked, but due to a software error it dispatched its lander on an entry angle which was too steep and

W. T. Huntress and M. Y. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer Praxis Books 1, DOl 10.1007/978-1-4419-7898-1 12,

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Launch date

1971

1972

14 Feb Luna 20 sample return

resulted in a crash. It worked perfectly for Mars 3 whose entry system placed the first successful lander on Mars, but after sending 20 seconds of uninterpretable data it fell silent. Both spacecraft entered orbit around the planet and transmitted images of its surface and data on its atmosphere, surface and plasma environment.

The US also had a major success at Mars in 1971. Mariner 9 was the lirst mission from this launch opportunity to arrive and became the first spacecraft to enter orbit. With more sophisticated cameras and systems, and an excellent instrument suite, its accomplishments completely eclipsed those of the much heavier Soviet orbiters.