The Soviet Venera 6 probe sent back 51 minutes of valuable data as it descended through Venus' thick atmosphere.
Identical to Venera 5, Venera 6 reached Venus after performing 63 communications sessions with Earth and one mid-course correction at a range of about 9.8 million miles (15.7 million kilometers) from Earth on March 16, 1969.
Its 893-pound (405-kilogram) lander separated from the main bus about 15,534 miles (25,000 kilometers) from the planet and entered the Venusian atmosphere at a velocity of about 7 miles per second (11.17 kilometers per second) at 06:05 UT on May 17, 1969.
The Venera 6 capsule transmitted data for 51 minutes before contact was lost, probably at an altitude of about 11 miles (18 kilometers). Pressure was 27 atmospheres at loss of contact, similar to that measured by Venera 5 at a much higher altitude indicating that Venera 6 may have come down over a mountain or high plateau. Landing coordinates were 5 degrees south latitude and 23 degrees north longitude.
Results from the Venera 5 and 6 missions, published by the Soviets in March 1970, seemed to confirm and sharpen earlier findings from Venera 4, suggesting that the planetary atmosphere consisted of 97 percent carbon dioxide, less than 2 percent nitrogen, and less than 0.1 percent oxygen.
Data from Venera 6 suggested the ground pressure was about 60 atmospheres and ground temperature was about 752 degrees Fahrenheit (400 degrees Celsius). This data compared with Venera 4’s readings which indicated pressure at 75 atmospheres and temperature at 932 degrees Fahrenheit (500 degrees Celsius).
Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.