Mars 6 was one of two landers launched by the Soviet Union during the 1973 launch window. The landers were very similar in design to the Mars 2 and Mars 3 landers dispatched by the Soviets in 1971, except that the spacecraft was now composed of a flyby vehicle (instead of an orbiter) and a lander. Mars 6 completed its first midcourse correction en route to Mars on 13 August 1973. A few days later, there was a major failure in the telemetry system that transmitted scientific and operations data from the spacecraft. Only two channels remained operational, neither of which provided the ground with any data on the status of the flyby vehicle's systems. Amazingly, the flyby spacecraft automatically performed all its functions, and on 12 March 1974, the lander successfully separated from its mother ship at a distance of 48,000 kilometers from Mars. Three hours later, it entered the Martian atmosphere. The parachute system deployed correctly at an altitude of 20 kilometers, and scientific instruments began to record data as the probe descended. Data seemed to indicate that the lander was rocking back and forth under its parachute far more vigorously than expected. Moments before expected landing, the ground lost contact with the probe. The last confirmed data was information on ignition of the softlanding engines at 08:58:20 UT. The probe landed at 09:11 UT at 23_54' south latitude and 19_25' west longitude. Later investigation never conclusively identified a single cause of loss of contact. Probable reasons included failure of the radio system or landing in a geographically rough area. All data from the Mars 6 lander was transmitted via the Mars 6 flyby bus, which also collected scientific information during its short flyby.
