Venera 4 was the first spacecraft to transmit data from a another planet’s atmosphere.
Venera 4 was the first spacecraft to transmit data from a planet’s atmosphere. It was also the first Venus probe built by the Lavochkin design bureau, although Lavochkin engineers retained the basic design layout of the earlier 3MV probes built under Chief Designer Sergey Korolev (1907-1966).
The spacecraft consisted of a main bus about 11.5 feet (3.5 meters) high and a 844-pound (383-kilogram) lander probe designed to transmit data as it descended through the Venusian atmosphere. This capsule could endure loads as high as 300 g’s and land on both land and liquid.
For atmospheric entry it was equipped with a thick ablative heat shield. Launch, for the first time, used an upgraded Blok L (4th stage), the Blok VL.
After a mid-course correction on July 29, 1967, Venera 4 approached Venus on Oct. 18, 1967. About 2 hours before arrival at Venus, at a distance of 27,962 miles (45,000 kilometers), on command from Earth, the spacecraft was properly oriented for entry.
The bus released the lander at 04:34 UT, and the latter entered the Venusian atmosphere at a velocity of about 7 miles per second (11 kilometers per second). The bus returned data for some time before being destroyed in the atmosphere.
The lander, meanwhile experienced as much as 300 g’s and reduced its speed to 689 feet per second (210 meters per second), at which point the parachute system was deployed. Simultaneously, the lander began to transmit information back to Earth.
Because the altimeter was designed to record pressures only up to 7.3 atmospheres, it went off-scale rather quickly. Temperature measurements from 91.4 degrees Fahrenheit to 504 degrees Fahrenheit (33 degrees Celsius to 262 degrees Celsius) continued to come back for 93 minutes as the probe slowly descended through the atmosphere.
Initially, Soviet scientists believed that the probe transmitted until contact with the surface, announcing that “a calculation of the rate of descent of the station until termination of transmission of data indicates that it continued transmitting until it actually touched the surface of the planet.” Later analysis of data showed that transmissions ceased at an altitude of about 17 miles (28 kilometers) when the high atmospheric pressure and temperatures damaged the probe. The inert probe impacted the surface near 19 degrees north latitude and 36 degrees east longitude.
The data implied that surface temperatures and pressure were 932 degrees Fahrenheit (500 degrees Celsius) and 75 atmospheres respectively.
Venera 4’s gas analyzers also found that the planet’s atmosphere was composed of 90 to 95 percent carbon dioxide (with a sensitivity of plus or minus 7 percent) with no nitrogen, which had previously been assumed would constitute most of the atmosphere.
Data from the ionizing densitometer showed that cloud cover in the Venusian atmosphere exists at altitudes below about 32 miles (52 kilometers) with the lower boundary at roughly 22 miles (35 kilometers).
The spacecraft bus measured the planet’s weak magnetic field and found no ring of radiation belts. It detected a very weak atmosphere of atomic hydrogen about 6,150 miles (9,900 kilometers) above the planet.
Noteworthy was Venera 4’s detection of the planet’s bow shock, identified a day before by Mariner 5 (and later confirmed by Venera 5).
The mission’s importance was underscored when NASA Administrator James E. Webb (1906-1992) issued a statement on Oct. 18, 1967, noting that the landing “represents an accomplishment any nation can be proud of.”
Researchers at NASA Ames Research Center were particularly interested in data from Venera 4, especially the effect of planetary atmosphere on the propagation of radio signals from the spacecraft, in anticipation of future NASA missions to Venus.
Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.