Venera 4 - The Mission

The Mission

Two nominally identical Venera 4-type probes were launched in June 1967. The first probe, Venera 4, was launched on 12 June from a Tyazheliy Sputnik (67-058B). A course correction was performed on 29 July when it was 12 million km away from Earth; otherwise the probe would have missed Venus. Although two such corrections had been planned, the first one was accurate enough and therefore the second correction was canceled. On October 18, 1967, the spacecraft entered the Venusian atmosphere with an estimated landing place near 19°N 38°E / 19°N 38°E / 19; 38.

The second, launched on 17 June, experienced a failure of one of its rocket stages and only managed to reach Earth orbit, reentering the Earth's atmosphere 8 days later. This probe was renamed Cosmos 167.

During entry into the Venusian atmosphere, the heat shield temperature rose to 11000 °C and at one point the cabin acceleration reached 300 G. The descent lasted 93 minutes. The capsule deployed its parachute at an altitude of about 52 km, and started sending data on pressure, temperature and gas composition back to Earth. The temperature control kept the inside of the capsule at -8 °C. The temperature at 52 km was recorded as 33 °C, and the pressure as less than 1 atm. At the end of the 26-km descent, the temperature reached 262 °C and pressure increased to 22 atmospheres, and the signal transmission terminated. The atmospheric composition was measured as 90-93% carbon dioxide, 0.4-0.8% oxygen, 7% nitrogen and 0.1-1.6% water vapor.

Misbehavior of the altimeter resulted in the value of initial altitude (deployment of the capsule's parachute and start of the measurements) being transmitted as 26 km. Therefore, some Earth observers interpreted the descent as having continued to the surface of Venus, which was quickly dismissed as inconsistent with other data. In particular, the pressure readings by the capsule were much too low for the Venusian surface.