The Venera 11 was a USSR unmanned space mission part of the Venera

Venera

The Venera series probes were developed by the Soviet Union between 1961 and 1984 to gather data from Venus, Venera being the Russian name for Venus...

 program to explore the planet Venus

Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

. Venera 11 was launched on 9 September 1978 at 3:25:39 UTC

Coordinated Universal Time

Coordinated Universal Time is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time. Computer servers, online services and other entities that rely on having a universally accepted time use UTC for that purpose...

.

Separating from its flight platform on December 23, 1978 the lander entered the Venus atmosphere two days later on December 25 at 11.2 km/s. 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 (0324 UT) on 25 December after a descent time of approximately 1 hour. The touchdown speed was 7 to 8 m/s. Landing coordinates are . Information was transmitted to the flight platform for retransmittal to earth until it moved out of range 95 minutes after touchdown.

Flight platform

After ejection of the lander probe, the flight platform continued on past Venus in a heliocentric orbit. Near encounter with Venus occurred on December 25, 1978, at approximately 34,000 km altitude. The flight platform acted as a data relay for the descent craft for 95 minutes until it flew out of range and returned its own measurements on interplanetary space.

Venera 11 flight platform carried solar wind detectors, ionosphere electron instruments and two gamma ray burst

Gamma ray burst

Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...

 detectors - the Soviet-built KONUS and the French

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

-built SIGNE 2. The SIGNE 2 detectors were simultaneously flown on Venera 12

Venera 12

The Venera 12 was an USSR unmanned space mission to explore the planet Venus. Venera 12 was launched on 14 September 1978 at 02:25:13 UTC. Separating from its flight platform on December 19, 1978, the lander entered the Venus atmosphere two days later at 11.2 km/s. During the descent, it...

 and Prognoz 7 to allow triangulation of gamma ray sources. Before and after Venus flyby, Venera 11 and Venera 12 yielded detailed time-profiles for 143 gamma-ray bursts, resulting in the first ever catalog of such events. The last gamma-ray burst reported by Venera 11 occurred on January 27, 1980

List of flight platform instruments and experiments:

• 30-166 nm Extreme UV Spectrometer
• Compound Plasma Spectrometer
• KONUS Gamma-Ray Burst Detector
• SNEG Gamma-Ray Burst Detector
• Magnetometer
• 4 Semiconductor Counters
• 2 Gas-Discharge Counters
• 4 Scintillation Counters
• Hemispherical Proton Telescope

The mission ended in February, 1980.

Lander

The lander carried instruments to study the temperature and atmospheric and soil chemical composition. A device called Groza detected lightning

Lightning

Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

on Venus. Both Venera 11 and Venera 12 had landers with two cameras, each designed for color imaging, though Soviet literature does not 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.

List of lander experiments and instruments:

• Backscatter Nephelometer
• Mass Spectrometer - MKh-6411
• Gas Chromatograph - Sigma
• X-Ray Fluorospectrometer
• 360° Scanning Photometer - IOAV
• Spectrometer (430-1170 nm)
• Microphone/Anemometer
• Low-Frequency Radio Sensor
• 4 Thermometers
• 3 Barometers
• Accelerometer - Bizon
• Penetrometer - PrOP-V
• Soil Analysis Device
• 2 Color Cameras
• Small solar batteries - MSB