Venera 11

Venera 11
	Seal of Venera 11
Operator	Soviet Academy of Sciences
COSPAR ID	1978-084A; 1978-084D
SATCAT no.	11020; 11027
Mission duration	Travel: 3 months and 16 days; Lander: 95 minutes
Spacecraft properties
Spacecraft	4V-1
Spacecraft type	4V-1 No. 360
Bus	4MV
Launch mass	4,447.3 kg (9,805 lb)
BOL mass	4,715 kg (10,395 lb)
Landing mass	760 kg (1,680 lb)
Dimensions	2.7 m × 2.3 m × 5.7 m (8.9 ft × 7.5 ft × 18.7 ft)
Start of mission
Launch date	September 9, 1978, 03:25:39 UTC
Rocket	Proton-K/D-1 8K82K
Launch site	Baikonur 81/23
End of mission
Last contact	February 1, 1980
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Semi-major axis	6,569 kilometers (4,082 mi)
Eccentricity	0.0312
Perigee altitude	177 kilometers (110 mi)
Apogee altitude	205 kilometers (127 mi)
Inclination	51.5°
Flyby of Venus
Spacecraft component	Venera 11 flight platform
Closest approach	25 December 1978
Distance	~35,000 kilometers (22,000 mi)
Venus lander
Spacecraft component	Venera 11 descent craft
Landing date	25 December 1978, 03:24
Landing site	14°S 299°E / 14°S 299°E (near Phoebe Regio)
	Venera ← Venera 10 Venera 12 →

The Venera 11 (Russian: Венера-11 meaning Venus 11) was a Soviet uncrewed space mission which was part of the Venera program to explore the planet Venus. Venera 11 was launched on 9 September 1978 at 03:25:39 UTC.^[2]

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 (03:24 UT) on 25 December after a descent time of approximately 1 hour. The touchdown speed was 7 to 8 m/s.^[3] Information was transmitted to the flight platform for retransmittal to Еarth until it moved out of range 95 minutes after touchdown.^[4] Landing coordinates are 14°S 299°E / 14°S 299°E / -14; 299.^[3]^[5]

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 35,000 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.^[6]

Venera 11 flight platform 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. 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:^[7]

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. Venera 11 is currently in heliocentric orbit, with perihelion of 0.69 AU, aphelion of 1.01 AU, eccentricity of 0.19, inclination of 2.3 degrees and orbital period of 284 days.

Lander

The lander carried instruments to study the temperature and atmospheric and soil chemical composition. A device called Groza was intended to search for lightning 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 some evidence of lightning,^[8] a high Ar³⁶/Ar⁴⁰ ratio, and the discovery of carbon monoxide at low altitudes.^[4]

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

References

^ ^a ^b ^c ^d Siddiqi, Asif A. (2018). Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016 (PDF). The NASA history series (second ed.). Washington, DC: NASA History Program Office. pp. 127–128. ISBN 978-1-62683-042-4. LCCN 2017059404. SP2018-4041.
^ "Venera 11". Archived from the original on 2015-01-21. Retrieved 2012-12-10.
^ ^a ^b "Venera 11 Descent Craft Launch and Orbital Information". NASA Space Science Data Coordinated Archive. Retrieved November 6, 2019.
^ ^a ^b "Venera 11 Descent Craft". NASA Space Science Data Coordinated Archive. Retrieved November 6, 2019.
^ "Venera 11 – Detail". Archived from the original on 2019-11-09. Retrieved 2012-12-10.
^ "Venera 11". NASA Space Science Data Coordinated Archive. Retrieved November 6, 2019.
^ Mitchell, Don P. "Drilling into the Surface of Venus". Retrieved 13 April 2013.
^ Lorenz, Ralph D. (2018-06-20). "Lightning detection on Venus: a critical review". Progress in Earth and Planetary Science. 5 (1): 34. Bibcode:2018PEPS....5...34L. doi:10.1186/s40645-018-0181-x. ISSN 2197-4284.