In 1985, Soviet engineers sent two balloons floating through Venus for 46.5 hours. Their motherships then used the planet’s gravity to chase Halley’s Comet

In 1985, two Soviet spacecraft carried out a major mission that took them from Venus to Halley’s Comet. Vega 1 and Vega 2 were designed to place landers on Venus, release balloons into its atmosphere, and then use Venusian gravity to fly their remaining buses past Halley.

The twin spacecraft were part of what was described as perhaps the most ambitious Soviet deep-space mission to date. The project was a cooperative effort involving the Soviet Union, Austria, Bulgaria, Hungary, East Germany, Poland, Czechoslovakia, France, and West Germany. The balloon gondolas were French-made.

Two balloons spent 46.5 hours in Venus’ atmosphere

Vega 1 released its 1,500-kilogram descent module on June 9, 1985, two days before atmospheric entry. As the lander descended through the Venusian atmosphere, it reached an altitude of 61 kilometers and released a helium-inflated plastic balloon with a gondola hanging underneath.


The balloon weighed around 20.8 kilograms. Partly controlled by ballast, it drifted through Venus’ atmosphere while its instruments measured temperature and pressure, vertical winds, atmospheric scattering and light levels. It transmitted atmospheric data back to a network of tracking antennas on Earth.

Vega 1’s balloon survived for 46.5 hours before operations ended because of battery failure.

Vega 2 released its own balloon upon entry into the atmosphere. The balloon flew through Venus’ atmosphere while collecting data and survived for 46.5 hours of data transmission.

The landers also reached the surface

Vega 1’s lander safely reached the surface at 03:02:54 UT on June 11, 1985. It landed at 7.2° north latitude and 177.8° longitude on Venus’ night side, in the Mermaid Plain north of Aphrodite, as per NASA's report titled 'A Chronology of Deep Space and Planetary Probes.'

The lander transmitted from the surface for 56 minutes. Its soil sample drill failed to complete its soil analysis, but its mass spectrometer returned important data.

Vega 2 reached Venus four days later, landing at 03:00:50 UT on June 15 in the northern region of Aphrodite. It transmitted from the surface for 57 minutes.

Unlike Vega 1, Vega 2 successfully collected and investigated a soil sample. The experiment identified an anorthosite-troctolite rock, which is rarely found on Earth but is present in the lunar highlands. The lander’s data also indicated that the area was probably the oldest explored by any Venera vehicle. Its mass spectrometer did not return any data.

From Venus to Halley’s Comet

After releasing their landers, the flyby probes continued toward Halley. Vega 1 flew past Venus at a range of 39,000 kilometers before heading for the comet. Following a course correction on February 10, 1986, it began formal comet studies on March 4, when it was 14 million kilometers from Halley.

On March 6, Vega 1 came within 8,889 kilometers of Halley at 07:20:06 UT. During the three-hour encounter, it took more than 500 pictures through different filters as it flew through the gas cloud around the comet’s coma. Although the spacecraft was battered by dust, none of its instruments were disabled. It collected information about Halley’s nucleus, dust production rate, chemical composition, and rotational rate.

Vega 2 began its encounter on March 7 by taking 100 photographs from 14 million kilometers away. Two days later, it reached its closest approach at 07:20 UT while traveling at 76.8 kilometers per second, slightly slower than Vega 1’s 79.2 kilometers per second.

During the encounter, Vega 2 took 700 images of the comet, with better resolution than those from Vega 1, partly because there was less dust outside the coma during its transit. The spacecraft sustained an 80% power loss during the encounter, compared with 40% for Vega 1.

Seven instruments between the two spacecraft were partially damaged, although none were incapacitated.

After further imaging sessions on March 10 and 11, Vega 2 finished its primary mission and headed into heliocentric orbit. Vega 1 carried out additional imaging on March 7 and 8 before heading out to deep space.