# Soviet Venus Missions

By Douglas M. Messier
Copyright © by National Science Teachers Association

The Soviet Union flew a series of largely successful robotic missions to Venus. These missions included orbiters, landers, and atmospheric probes. The nation achieved a series of historic space firsts during its exploration of Earth's "sister" planet.

In 1967, the country became the first to place a probe into the Venusian atmosphere. The Venera 4 spacecraft, launched on June 12, 1967, released a 383-kilogram (845-pound) probe. The 1-meter (39-inch) probe descended under a parachute for 94 minutes, relaying data until it ceased transmissions at an altitude of 25 kilometers (15.5 miles). The probe's sensors returned data indicating the atmosphere was 90 to 95 percent carbon dioxide.

Venera 5 and 6, launched five days apart in January 1969, also contained atmospheric probes. The probes, which arrived in May 1969, transmitted data indicating that the atmosphere was composed of 93 to 97 percent carbon dioxide, 2 to 5 percent nitrogen, and less than 4 percent oxygen. The probes possessed smaller parachutes designed to speed their descents to the surface. However, the spacecraft were destroyed by the hot, high-pressure atmosphere before they could land.

The Soviets were more successful with Venera 7 and 8. Venera 7's 495-kilogram (1,091-pound) atmospheric probe reached the surface in December 1970, and transmitted for 23 minutes. It measured a surface temperature of 475°C (887°F), hot enough to melt lead. The probe measured the surface pressure at 90 bar. This pressure is equivalent to that found 2.4 kilometers (1.5 miles) beneath the ocean.

Venera 8, launched in March 1972, also successfully landed a probe that survived for 50 minutes. The probe, which was the first to land on the day side, returned data on light levels and soil density. It also measured wind speed variations during descent of:

- 100 meters/second (224 miles per hour) above 48 kilometers (30 miles);
- 40 to 47 meters/second (89 miles per hour) at 42 to 48 kilometers (26 to 30 miles), and,
- 1 meter/second (2 miles per hour) below 10 kilometers (6 miles).

In June 1975, the Soviet Union sent two sophisticated spacecraft, Venera 9 and 10, to Venus in the most ambitious effort to date. Each spacecraft included an orbiter and a soft lander. These missions marked the first time a spacecraft had orbited Venus.

The two probes landed and transmitted the first black and white images of the surface. The Venera 9 landing site showed sharp-edged, flat rocks and basaltic terrain. The terrain at the Venera 10 landing site was more eroded than the terrain at the other landing site. Venera 9 lasted for 53 minutes on the surface, while Venera 10 transmitted data for 65 minutes.

The orbiters photographed the Venusian cloud tops, studied the upper atmosphere, and measured the characteristics of space near the planet. Differences in cloud layers were discovered at 57 to 70 kilometers (35 to 44 miles), 52 to 57 kilometers (32 to 35 miles), and 49 to 52 kilometers (30 to 32 miles).

The Soviet Union launched Venera 11 and 12 in 1978. This was a repetition of the Venera 8 and 9 missions with improved sensors and equipment. The Venera 11 probe returned data for 95 minutes from the surface, although its imaging system failed. Venera 12 lasted 110 minutes on the surface, recording electrical discharges that indicated lightning was present on Venus.

The Soviets launched a major scientific assault on Venus during the early 1980's. The USSR launched six probes to the planet during a three-year period, undertaking some innovative scientific exploration.

Venera 13 and 14 were 5,000-kilogram (11,000-pound) flyby/landers launched in late 1981. Venera 13 landed on Venus on March 1, 1982, and its twin touched down four days later. The landers returned black and white pictures and the first color panoramic views of the Venusian surface. They also conducted soil analysis using an x-ray fluorescence spectrometer. Venera 13's sample was determined to be leucite basalt, a rare rock type on the Earth. Venera 14's sample was determined to be tholeiitic basalt, similar to that found at mid-ocean ridges on the Earth.

In 1983, two orbiters were sent to Venus. Venera 15 arrived at Venus on October 10, 1983, followed by Venera 16 four days later. Their high-resolution, synthetic aperture radar (SAR) systems were able to peer beneath the clouds to produce images at 1 to 2 kilometers (.6 to 1.2 miles) in resolution. Venera 15 and 16 produced a map of the northern hemisphere from the pole to 30°N. They found several hot spots, possibly caused by volcanic activity.

The last Soviet exploration of Venus took place in 1985 with the Vega 1 and 2 missions. These missions were notable for several reasons. The spacecraft had dual missions to explore both Venus and Comet Halley. Furthermore, the Soviets opened the flights to substantial participation from Western nations for the first time.

The original plan was for the Vega spacecraft to drop off Venera-type landers and balloons to investigate the Venusian middle-cloud level. However, at a cocktail party in 1980, Jacques Blamont, a French scientist who was working on the project, said that it would be relatively easy to redirect the spacecraft for a flyby of Comet Halley in 1986. The Soviets accepted the recommendation and set about modifying the spacecraft.

Blamont was one of many foreign scientists invited to participate in the Vega program. The Soviets received considerable cooperation on hardware development and mission operations from Western European nations. This was part of an effort to open a relatively closed space program to outside participation. Previously, the Soviets had undertaken limited cooperative activities with Eastern European nations and France.

American cooperation on this mission was at an unofficial level, in part due to political tensions between the nations during the early 1980's. The Soviets reached an agreement with the European Space Agency to use America's Deep Space Network for tracking the Vega probes when they reached Comet Halley. John A. Simpson, an American scientist from the University of Chicago, contributed comet-dust detectors. In order to avoid political problems, he had the instruments assembled in West Germany and publicized as a West German contribution to program.

The two spacecraft were launched six days apart in December 1984. Vega 1 flew past Venus on June 11, 1985, followed by Vega 2 four days later. Both spacecraft dropped off their probes and then continued on to their encounter with Comet Halley.

The Vega 1 soil experiment failed. Vega 2's soil experiment sampled anorthosite-troctolite, which is found in the lunar highlands but is rare on Earth. Both balloons floated in the atmosphere for about 48 hours at an altitude of 54 kilometers (34 miles). Vega 1 and 2 encountered downward gusts of 1 meter/second (2 miles per hour) and wind velocities of up to 240 kilometers/hour (150 miles per hour).

Vega 1's flyby of Comet Halley took place on March 6, 1986. The Vega 2 encounter occurred on March 9. The Soviet spacecraft were part of an international armada that included two Japanese probes, Sakigake and Suisei, and a European spacecraft, Giotto. The spacecraft took photographs and made measurements of the comet and its environment. The Vega probes are now in solar orbit.

The Soviet Union did not launch any further probes to Venus. When the USSR dissolved in 1991, Russia inherited most of the space program. The nation has been forced to cut back on space exploration because of budget problems. Russia's future plans for exploring Earth's "sister" planet are uncertain at the moment.

## References

Gatland, Kenneth, consultant and chief author, The Illustrated Encyclopedia of Space Technology, Harmony Books, New York, 1981.

Planetary Science Database, National Space Science Data Center (NSSDC), National Aeronautics and Space Administration, Greenbelt, Maryland. World Wide Web: http://nssdc.gsfc.nasa.gov/nssdc/nssdc_home.html.

Wilford, John Noble, Mars Beckons, Alfred A. Knopf, New York, 1990.

Space History

##### Calvin J. Hamilton