Mission Type: Flyby, Lander
Launch Vehicle: 8K82K + Blok DM (Proton-K no. 296-01 / Blok DM no. 3L)
Launch Site: NIIP-5 / launch site 81L
Spacecraft Mass: 4,450 kg
Spacecraft Instruments:
Flyby bus: 1) plasma spectrometer; 2) Konus gamma-ray detector; 3) Sneg-2MZ gamma- and x-ray burst detector; 4) ultraviolet spectrometer; 5) magnetometer; 6) solar wind detectors; and 7) cosmic-ray detectors
Lander: 1) imaging system; 2) Sigma gas chromatograph; 3) mass spectrometer; 4) gamma-ray spectrometer; 5) Groza lightning detector; 6) temperature and pressure sensors; 7) nephelometer; 8) anemometer; 9) optical spectrophotometer; 10) remote soil collector; 11) x-ray fluorescence cloud aerosol analyzer; and 12) Arakhis x-ray fluorescence spectrometer and drill
References:
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi

National Space Science Data Center, http://nssdc.gsfc.nasa.gov/

Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

Venera 11 was one of two identical probes (the other being Venera 12) that followed up on the highly successful Soviet missions to Venus in 1975.

Veneras 11 and 12 differed from their predecessors principally in the fact each carried a flyby bus/lander combination instead of the previous orbiter/lander combination. Engineers reverted to the flyby combination partly because of the weight limitations of the 1978 launch window, but also because flyby probes afforded better transmission time for landers. Several of the scientific instruments were also modified and new ones added.

Venera 11 arrived at Venus after two course corrections on 16 September and 17
December 1978. On 23 December 1978, the lander separated from the flyby probe and entered the Venusian atmosphere two days later.

The lander probe safely landed on Venus at 03:24 UT on 25 December 1978 and then relayed 95 minutes of data from the surface. Landing coordinates were 14° south latitude and 299° longitude. The point of cutoff was determined by the range of visibility of the flyby probe.

A soil-drilling instrument collected soil for chemical and physical analysis, but soil analysis was unsuccessful because the soil was not properly deposited to an examination container for analysis (probably due to leaking air that disturbed the soil). The lander also failed to take color panoramas of the Venusian surface due to a failure of the lens covers of the camera system to open. While extensive
atmospheric data was later released, the Soviets have published relatively little data from surface measurements.

The flyby probe entered heliocentric orbit after flying past the planet at a range of 35,000 kilometers.