This project turned out to be devoted to the research of two space objects at once - the planet Venus and the comet Halley.
15 and 21 December 1984 of the year, from the BAYKONUR cosmodrome, automatic interplanetary stations (AMS) Vega-1 and Vega-2 were launched. They were put on the flight path to Venus by the four-rocket carrier Proton-K.
The AMS "Vega-1" and "Vega-2" consisted of two parts - the flying vehicle with a mass of 3170 kg and the descent vehicle with a mass of 1750 kg. The landing gear with a mass of 680 kg and a floating balloon station (PAS) were the payload of the descent vehicle, the mass of which together with the helium filling system was no more than 110 kg. The latter has become an important element of the project. Upon reaching the planet, the PAS was supposed to separate from the descent vehicle and rise into the atmosphere of Venus. The drift of the PAS was to take place for 2-5 of the day at 53-55 km altitude, in the cloud layer of the planet. The span apparatuses, after the fulfillment of the target task (the discharge of the descending apparatuses), were further redirected to Halley's comet.
The road to Venus was already well mastered by many Soviet interplanetary stations, beginning with Venus-2 and ending with Venus-16. Therefore, the flight of both stations "Vega" was almost without complications. On the route of the flight, scientific research was carried out, including the study of interplanetary magnetic fields, solar and cosmic rays, X-rays in space, the distribution of the components of neutral gas, and the registration of dust particles. The duration of the flight from Earth to Venus was for the station “Vega-1” 178 days, and for “Vega-2” - 176 days.
Two days before the approach, the descent module was separated from the Vega-1 automatic station, while the spacecraft (span) had gone onto the flight path. This correction was an integral part of the gravitational maneuver necessary for the subsequent flight to Halley's comet.
11 June 1985, the descent vehicle of the Vega-1 station entered the atmosphere of Venus on the night side. After the upper hemisphere was separated from it, in which the balloon was in the folded state, each part performed an autonomous descent. A few minutes later it began filling the balloon with helium. As the helium warms up, the probe floated to the design height (53-55 km).
The landing gear made a parachute descent and at the same time transmitted scientific information to the Vega-1 spacecraft with the subsequent retransmission of information to Earth. After 10 minutes after entering the atmosphere at an altitude of 46 km, the dropping parachute was reset, after which the descent was already on the aerodynamic brake flap. At an altitude of 17 km, the atmosphere of Venus presented a surprise: the landing alarm worked. Perhaps the blame for all was the strong turbulence of the atmosphere at altitudes 10-20 km. Subsequent calculations showed that the sudden eddy flow with a speed of more than 30 m / s could have been the cause of the premature landing of the landing alarm. But most importantly, the cyclogram of the operation of devices on the surface of the planet, including the sampling device (GZU), was launched using this signaling device. It turned out that the drill drilled the air, and not the ground of Venus.
After 63 minutes of descent, the landing gear descended to the surface of the planet in the lowland part of the Mermaid plain of the northern hemisphere. Although there was no benefit from the GZU anymore, other scientific instruments conveyed valuable information. The duration of receiving information from the descent vehicle after landing was 20 minutes. However, no lander has attracted worldwide attention. Scientists have been waiting for the appearance of a signal from a floating balloon station. After reaching the drift height, the transmitter turned on, and the radio telescopes of the whole world began to receive the signal. To provide reception of scientific information from the balloon probe, two radio telescope networks were created: the Soviet, coordinated by the Space Research Institute of the USSR Academy of Sciences, and the international, coordinated by CNES (France).
During 46 hours, radio telescopes from around the world were receiving a signal from a balloon probe in the atmosphere of Venus. During this time, the PAS overcame the distance 11500 km along the equator with an average wind speed of 69 m / s along the equator, measuring temperature, pressure, vertical gusts of wind and average illumination along the flight path. The PAS flight began from the middle of the night, and finished its work on the day side. The work from the first floating balloon station has just been completed, and the next AMC - Vega-2 has already flown to Venus. 13 June 1985 of the year was the separation of its descent and flying apparatuses, with the latter being withdrawn with the help of its own propulsion system to the flying trajectory.
15 June 1985 of the year, as a carbon copy, underwent operations for entering the descent vehicle into the atmosphere of Venus and receiving information from it, right up to landing, detaching a floating balloon station and exiting it to the height of the drift. The only difference was the timely triggering of the landing alarm at the moment of touching the surface. As a result, the soil collecting device worked out normally, which made it possible to analyze the soil at the landing site located in the foothills of the land of Aphrodite (southern hemisphere) at 1600 km from the landing site of the Vega-1 descent module.
The second PAS also drifted at an altitude of 54 km, and in 46 hours it overcame a path in 11 thousand km. Summarizing the interim results of the flight of the Soviet interplanetary stations "Vega-1" and "Vega-2", we can say that we managed to make a qualitatively new step in the development of Venus. With the help of small balloon probes designed and manufactured in the NPO. S.A. Lavochkin, the atmospheric circulation of the planet was studied at an altitude of 54-55 km, where the pressure is 0,5 of the atmosphere, and the temperature is + 40 ° С. This altitude corresponds to the densest part of the cloud layer of Venus, in which, as was supposed, the mechanisms supporting the rapid rotation of the atmosphere from east to west around the planet — the so-called superrotation of the atmosphere — should appear more clearly.
Shortly after the passage of Venus, the automatic stations Vega-1 and Vega-2 and the end of the PSN 25 and 29 on June 1985 were corrected, respectively, by the trajectory of the space (flying) vehicles with which they were directed to Halley's comet. Usually, interplanetary stations that delivered the lander to the atmosphere of Venus continued their flight in heliocentric orbit, carrying out an optional scientific program. This time it was necessary to arrange a meeting with the comet of Halley at a given time in the appointed place. Therefore, since the discovery of the comet by ground-based telescopes, it was observed by observatories and astronomers around the world. In addition, interferometric measurements were regularly carried out not only to determine the trajectory of the vehicles themselves, but also to plot the course of the European Giotto interplanetary station, which had a meeting with the comet on 8 days later, as part of the Lotsman project.
As the target approached, the relative position of the vehicles and the comet was clarified. 10 February 1986 of the year was corrected trajectory of the station "Vega-1". As for “Vega-2”, the deviation from the specified trajectory was within the allowable range, and they decided to abandon the last correction. After the February 12 correction on Vega-1 and February 15 on Vega-2, respectively, the automatic stabilized platforms (ASP-G) of the devices were opened and removed from the transport position, and the calibrations of the television system and ASP-G according to Jupiter were carried out. In the days remaining before the meeting with the comet, the functioning of ASP and G and all scientific equipment was checked.
March 4 1986, when the distance from Vega-1 station to Halley's comet was 14 million km, the first comet session took place. After pointing the platform at the comet's core, it was shot with a narrow-angle camera. The next time 5 was turned on in March, the distance to the comet's core was already 7 million km. The expedition culminated in March 6 of 1986. 3 hours before the closest approach to the comet, scientific instruments were included for its study. At this point, the distance to the comet was almost 760 thousand. Km. For the first time the spacecraft was at such a short distance from the comet.
However, this was not the limit, as the Vega-1 was rapidly approaching the goal of its journey. After targeting TSA-G to the nucleus of the comet, a survey was started in tracking mode according to information from the television system, as well as the study of the nucleus of the comet and the gas-dust envelope surrounding it, using the whole complex of scientific equipment. Information was transmitted to Earth in real time at a speed of 65 kbaud. The incoming images of the comet were immediately processed and displayed on the flight control center and the Space Research Institute. Using these images, it was possible to estimate the size of the comet's nucleus, its shape and reflectivity, and observe the complex processes inside the gas and dust coma. The closest approach of the Vega-1 station to the comet was 8879 km.
The total duration of the span session was 4 hours 50 minutes. During the passage, the spacecraft was subjected to strong effects of cometary particles at a collision speed of 78 km / s. As a result, the power of the solar battery fell by almost 45%, and at the end of the session, the triaxial orientation of the device also failed. By 7, the triaxial orientation was restored in March, which allowed us to carry out another cycle of studying Halley's comet, but on the other side. In principle, it was planned to hold two sessions to study the cometary station "Vega-1" on departure, but the last of them did not hold, so as not to interfere with the second device.
Work with the second unit was carried out in a similar pattern. The first "cometary" session was held on March 7 and passed without comment. On this day, the comet was studied at once by two vehicles, but from different distances. But in the second session, held on the International Women's Day 8 in March, due to an error, the images of the comet were not obtained. Not without incident and during the 9 flight session in March. It began the same way as the Vega-1 flyby session. However, half an hour before the closest approach, which was 8045 km, a failure occurred in the platform control system. The situation was saved by the automatic activation of the backup control loop of ASP-H. As a result, the study program of comet Halley was able to complete. The total duration of the span of the Vega-2 session was 5 hours 30 minutes.
Although the drop in solar power after meeting the comet was the same 45%, this did not prevent another two sessions of studying the comet on departure - March 10 and 11. As a result of research by Soviet automatic stations Vega-1 and Vega-2, Halley's comet obtained unique scientific results, including some 1500 images. For the first time, spacecraft passed at such a close distance from a comet. For the first time it was possible to look at a close distance at one of the most mysterious bodies in the solar system. However, not only this exhausted the contribution of the stations "Vega-1" and "Vega-2" to the international program for the study of comet Halley.
During the flight of the stations, up to their closest approach to the comet, interferometric measurements were carried out as part of the Lotsman project. This allowed the Western European interplanetary station "Giotto" to be held at a distance of 605 km from the cometary nucleus. However, already at a distance of 1200 km as a result of an impact with a fragment of a comet at the station, the camera was out of order, and the station itself lost its orientation. However, Western European scientists were able to obtain unique scientific information.
Two Japanese interplanetary stations, Susi and Sakigake, also contributed to the study of comet Halley. The first of these, 8 in March, made the flyby of Halley’s comet at a distance of 150 thousand km, and the second passed through March at a distance of 10 million km.
The brilliant results of the study of comet Halley by the automatic interplanetary stations Vega-1, Vega-2, Giotto, Susi and Sakigake caused a wide international public response. An international conference dedicated to the results of the project was held in Padua (Italy).
Although the flight program of the automatic stations Vega-1 and Vega-2 was completed with the flight of Comet Halley, they continued their flight in heliocentric orbit, simultaneously investigating the meteor showers of the Comet Deining-Fujikawa, Bisle, Blanpeyna and the same Comet Halley. The last communication session with the station "Vega-1" was held on January 30 1987. It was recorded the complete consumption of nitrogen in gas balloons. Station "Vega-2" lasted longer. The last session, in which the teams were on board, was held on 24 March 1987.