Vega (space probe)

Model of the Vega-1 probe, Dulles International Airport , USA

Postage stamps of the USSR with Vega motif, 1984

Vega ( Russian Вега ) was a Soviet research mission with two separate space probes to the planet Venus and Halley's Comet . The name plays with that of the popular star Vega and is an abbreviation of the first two letters of Венера = Venera = Venus and Галлей = Gallej = Halley. Both space probes were launched in 1984 and implemented with broad international participation from both Eastern and Western European countries.

mission

After completion of the largely successful Venera - space probes that led Soviet Union between 1984 and 1986 two more planetary spaceflight by: Vega 1 and Vega 2 .

Two mother probes should first fly past Venus . A landing probe and a balloon should be released. The lander was supposed to land on the surface, a maneuver that the USSR had successfully carried out eight times between 1970 and 1982 (cf. Venera ). The balloon represented something new. Hung with instruments, it should be driven back and forth through the Venusian atmosphere , depending on where the winds would take it. The two mother probes should then head for Comet Halley and explore it up close.

The two Vega probes were the first and remained the only Soviet probes that were supposed to fly to two completely different objects (Venus and Halley). There was also strong international participation in this mission: In addition to the Eastern Bloc states GDR , Poland , Czechoslovakia , Hungary and Bulgaria , the Western European states France , Austria and the Federal Republic of Germany , the latter for the first time on a Soviet probe, were represented. The probe had numerous technical innovations, such as a scan platform with the camera that was independent of the fuselage, or the CCD technology for image capture , which was used for the first time in an interplanetary probe .

Both probes weighed 4950 kg when launched and were launched from the Baikonur Cosmodrome with a Proton rocket . The images of the launch were the first images of the Proton rocket published by the Soviet Union at the time. As a result of international cooperation, the spacecraft launches were announced in advance for the first time in the history of the USSR.

The balloons

The balloons of the Vega probes were the first and so far only balloons used on another celestial body. They were made in France and deployed and ejected at an altitude of 54 km. The balloons were 3.4 m in diameter and weighed 25 kg. A balloon carried a 5 kg payload on a 12 m long rope with sensors for determining temperature, pressure, vertical wind speed, brightness and visibility of the atmosphere and for detecting lightning. The power supply came from batteries. Each balloon was launched on the night side of Venus and was driven only by the winds of the Venusian atmosphere; his path was therefore unpredictable. The balloon was tracked through a network of twelve ground stations, six of which were outside the Soviet Union. As soon as the balloon reached the day side of Venus, it was heated by the sunlight and burst.

course

Stage scheme for the Vega missions

Vega 1 successfully left the earth on December 15, 1984, as did the sister probe Vega 2 on December 21, 1984.
Vega 1 passed Venus on June 11, 1985 , and Vega 2 did the same on June 14, 1985.
The Venus landings of the Vega-1 and Vega-2 landing probes also took place on June 11 and 14, 1985. Both probes reached the surface and transmitted data from there for 56 and 57 minutes.
Furthermore, on June 11 and 14, 1985, the two balloons were launched. The Vega 1 balloon flew for 46½ hours, and that of Vega 2 for 60 hours before contact was broken.
The passage at Comet Halley took place at Vega 1 on March 6, 1986 at a distance of 8890 kilometers, at Vega 2 on March 9, 1986 at a distance of 8030 kilometers.
After the Halley rendezvous, both probes were turned off.

Results

Vega 1 and 2 were among the most complex space projects in the Soviet Union. Although only the Venus balloons provided important new results (the two countries played a subordinate role) and the successful flyby of Halley was masked by the even more successful flyby of the European probe Giotto , the Soviets at least had the high standard of their space technology in the 1980s demonstrated.

With the help of the measurement technology, the wind speeds could be determined with an accuracy of 2 km / h: The cyclones that drove the balloons in front of them were up to 250 km / h and repeatedly hurled the balloons vertically several hundred meters up and down. The fact that the middle cloud layer was as stormy as suspected by remote observations could thus be confirmed, as was the east-west direction, which on the day side ultimately led to the bursting of the balloons due to thermal expansion. The thickness of the middle layer of the atmosphere was determined to be 22 km, and tiny droplets of concentrated sulfuric acid were found to be the main components.
The two tons of heavy landing probes had successfully touched down on the night side of the equator near the largest Venus continent, Aphrodite Terra . The soil samples obtained by automatically operating drills were subjected to the X-ray fluorescence method within the probes and resulted in magnesium and iron as main components, comparable to terrestrial basalts from lava flows. The floor temperature was approx. 460 ° C with a pressure of approx. 90 bar. Nevertheless, the probes worked for about 20 minutes and transmitted the measurement data until they became inoperable due to the environment, which was hostile to life and also hostile to technology.

Incidentally, thanks to the data transmitted by the Vega probes, Giotto was able to successfully improve its approach path, so that the core of Halley's comet could be photographed.

The Vegas was originally intended to be the prelude to a whole series of missions by the Soviet Union. Involuntarily, Vega 1 and 2 instead became the Soviet Union's last successful planetary missions. On the one hand, because the later ambitious projects Fobos 1 and 2 as well as Mars 96 failed, and on the other hand, because of the desperate economic situation in Russia, the Soviet Union could not be inherited in this area.