Venera 11

Separating from its flight platform on December 23, 1978 it entered the Venus atmosphere two days later on December 25 at 11.2 km/sec. During the descent, it employed aerodynamic braking followed by parachute braking and ending with atmospheric braking. It made a soft landing on the surface at 06:24 Moscow time on 25 December after a descent time of approximately 1 hour. The touchdown speed was 7-8 m/s. Information was transmitted to the flight platform for retransmittal to earth until it moved out of range 95 minutes after touchdown.

The lander carried instruments to study the temperature and atmospheric and soil chemical composition. A device called Groza detected lightning on Venus. Both Venera 11 and Venera 12 had landers with two cameras, each designed for color imaging, though Soviet literature doesn't mention them.
Each failed to return images when the lens covers did not separate after landing due to a design flaw. The soil analyzer also failed.
A gas chromatograph was on board to measure the composition of the Venus atmosphere, as well as instruments to study scattered solar radiation. Results reported included evidence of lightning and thunder, a high Ar³⁶/Ar⁴⁰ ratio, and the discovery of carbon monoxide at low altitudes.

Venera 11 also carried solar wind detectors, ionosphere electron instruments and two gamma ray burst detectors - the Soviet-built KONUS and the French-built SIGNE 2. The SIGNE 2 detectors were simultaneously flown on Venera 12 and Prognoz 7 to allow triangulation of gamma ray sources. The mission ended in February, 1980.