This project turned out to be devoted to the study of two space objects at once - the planet Venus and Halley's comet.
On December 15 and 21, 1984, the automatic interplanetary stations (AMS) Vega-1 and Vega-2 were launched from the BAIKONUR cosmodrome. They were placed on a flight path to Venus by a four-stage Proton-K launch vehicle.
AMS "Vega-1" and "Vega-2" consisted of two parts - a flight vehicle with a mass of 3170 kg and a descent vehicle with a mass of 1750 kg. The payload of the descent vehicle was a landing vehicle with a mass of 680 kg and a floating balloon station (PAS), the mass of which, together with the helium filling system, was no more than 110 kg. The latter became an important element of the project. Upon reaching the planet, PAS was supposed to separate from the descent vehicle and ascend into the atmosphere of Venus. The PAS drift was supposed to take place for 2-5 days at an altitude of 53-55 km, in the cloudy layer of the planet. The flying vehicles, after completing the target task (dropping the descent vehicles), were then redirected to Halley's comet.
The road to Venus was already well mastered by many Soviet interplanetary stations, from Venera-2 to Venera-16. Therefore, the flight of both Vega stations proceeded practically without complications. On the flight route, scientific research was carried out, including the study of interplanetary magnetic fields, solar and cosmic rays, X-rays in space, the distribution of neutral gas components, as well as the registration of dust particles. The duration of the flight from Earth to Venus was 178 days for the Vega-1 station, and 176 days for the Vega-2 station.
Two days before the approach, the descent module was separated from the automatic station "Vega-1", while the spacecraft (flyby) itself went on a flyby trajectory. This correction was an integral part of the gravitational maneuver required for the subsequent flight to Halley's comet.
On June 11, 1985, the descent vehicle of the Vega-1 station entered the atmosphere of Venus on the night side. After separating the upper hemisphere from it, in which the balloon probe was folded, each part performed an autonomous descent. In a few minutes the balloon was filled with helium. As the helium warmed up, the probe floated to the calculated altitude (53-55 km).
The lander performed a parachute descent and simultaneously transmitted scientific information to the Vega-1 spacecraft with subsequent relaying of the information to Earth. 10 minutes after entering the atmosphere at an altitude of 46 km, the braking parachute was dropped, after which the descent took place on the aerodynamic brake flap. At an altitude of 17 km, the atmosphere of Venus presented a surprise: the landing alarm went off. Probably, the strong turbulence of the atmosphere at altitudes of 10-20 km was to blame. Subsequent calculations showed that a sudden vortex flow with a velocity of more than 30 m / s could serve as the cause of the early triggering of the landing signal. But most importantly, this signaling device triggered a cyclogram of the operation of devices on the planet's surface, including the soil intake device (GDU). It turned out that the drill was drilling the air, not the soil of Venus.
After 63 minutes of descent, the lander landed on the planet's surface in the low-lying part of the Rusalka Plain in the northern hemisphere. Although there was no longer any benefit from the GDU, other scientific instruments conveyed valuable information. The duration of receiving information from the descent vehicle after landing was 20 minutes. However, it was not the lander that attracted everyone's attention. Scientists were waiting for a signal from a floating balloon station. After reaching the drift altitude, the transmitter turned on, and radio telescopes around the world began to receive the signal. To ensure the reception of scientific information from the balloon probe, two radio telescope networks were created: the Soviet one, coordinated by the Space Research Institute of the USSR Academy of Sciences, and the international one, coordinated by CNES (France).
For 46 hours, radio telescopes around the world were receiving a signal from a balloon probe in the atmosphere of Venus. During this time, the PAS, under the influence of the wind, covered the distance of 11,500 km along the equator at an average speed of 69 m / s, measuring temperature, pressure, vertical gusts of wind and average illumination along the flight path. The PAS flight started from the midnight area and ended up on the day side. The work with the first floating balloon station had just finished, and the next AMS, Vega-2, was already flying up to Venus. On June 13, 1985, its descent and flight vehicles were separated, with the latter being withdrawn to the flight path with the help of its own propulsion system.
On June 15, 1985, as a blueprint, operations were carried out to enter the descent vehicle into the atmosphere of Venus and receive information from it, up to landing, separation of the floating balloon station and its exit to the drift altitude. The only difference was the timely triggering of the landing indicator at the moment of touching the surface. As a result, the soil intake device worked normally, which made it possible to analyze the soil at the landing site located in the foothills of the land of Aphrodite (southern hemisphere) 1600 km from the landing site of the Vega-1 descent module.
The second PAS also drifted at an altitude of 54 km and covered a distance of 11 thousand km in 46 hours. Summing up the intermediate results of the flight of the Soviet interplanetary stations "Vega-1" and "Vega-2", we can say that it was possible to make a qualitatively new step in the exploration of Venus. With the help of small balloon probes, developed and manufactured at NPO im. S. A. Lavochkin, the circulation of the planet's atmosphere was studied at an altitude of 54-55 km, where the pressure is 0.5 atmospheres, and the temperature is + 40 ° C. This height corresponds to the densest part of the cloud layer of Venus, in which, as was assumed, the action of the mechanisms supporting the rapid rotation of the atmosphere from east to west around the planet, the so-called super-rotation of the atmosphere, should be more clearly manifested.
Soon after the passage of Venus, the automated probes Vega-1 and Vega-2 and the completion of the PAS operation on June 25 and 29, 1985, respectively, corrected the trajectory of the spacecraft (flyby), with the help of which they were directed to Halley's comet. Usually, interplanetary stations that delivered descent vehicles to the atmosphere of Venus continued to fly in a heliocentric orbit, carrying out an optional scientific program. This time it was required to ensure a meeting with Halley's comet at a given time in an agreed place. Therefore, starting from the moment the comet was discovered by ground-based telescopes, its observations were carried out by observatories and astronomers around the world. In addition, interferometric measurements were regularly carried out not only to determine the trajectory of the spacecraft themselves, but also to plot the course of the European interplanetary station "Giotto", in which the meeting with the comet was supposed to take place 8 days later, within the framework of the "Pilot" project.
As they approached the target, the relative position of the spacecraft and the comet was clarified. On February 10, 1986, the trajectory of the Vega-1 station was corrected. As for Vega-2, the deviation from the specified trajectory turned out to be within the permissible range, and they decided to abandon the last correction. After the correction was carried out on February 12 on Vega-1 and on February 15 on Vega-2, the automatic stabilized platforms (ASP-G) of the vehicles were respectively opened and removed from the transport position, and the television system and ASP-G were calibrated according to Jupiter. In the days remaining before the meeting with the comet, the functioning of the ASP-G and all scientific equipment was checked.
On March 4, 1986, when the distance from the Vega-1 station to Halley's comet was 14 million km, the first “comet” session took place. After the platform was aimed at the comet's nucleus, it was filmed with a narrow-angle camera. The next time it was turned on on March 5, the distance to the comet's nucleus was already 7 million km. The climax of the expedition came on March 6, 1986. 3 hours before the closest approach to the comet, scientific instruments were turned on for its study. At this moment, the distance to the comet was almost 760 thousand km. This is the first time a spacecraft has been so close to a comet.
However, this was not the limit, as the Vega-1 was rapidly approaching the destination of its journey. After aiming the ASP-G at the comet's nucleus, shooting began in the tracking mode using information from the television system, as well as studying the comet's nucleus and the gas-dust envelope surrounding it using the entire set 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 screens at the Mission Control Center and the Space Research Institute. From these images, it was possible to estimate the size of the comet's nucleus, its shape and reflectivity, and to observe complex processes inside the gas and dust coma. The maximum approach of the Vega-1 station with the comet was 8879 km.
The total duration of the flight session was 4 hours 50 minutes. During the passage, the spacecraft was strongly affected by cometary particles at a collision speed of 78 km / sec. As a result, the power of the solar battery dropped by almost 45%, and at the end of the session there was also a failure of the three-axis orientation of the vehicle. By March 7, the triaxial orientation was restored, which made it possible to carry out another cycle of studying Halley's comet, but from the other side. In principle, it was planned to conduct two sessions of studying the comet by the Vega-1 station on departure, but the last of them was not carried out so as not to interfere with the second spacecraft.
The work with the second apparatus was carried out in a similar way. The first "comet" session was carried out on March 7 and passed without comment. On this day, the comet was studied by two devices at once, but from different distances. But in the second session, held on International Women's Day on March 8, due to a pointing error, no images of the comet were obtained. There were some adventures during the flight session on March 9. It began in the same way as the flight session of Vega-1. However, half an hour before the maximum approach, which was 8045 km, there was a failure in the platform control system. The situation was saved by the automatic activation of the ASP-G backup control loop. As a result, the program for the study of Halley's comet was fully completed. The total duration of the Vega-2 flight was 5 hours 30 minutes.
Although the drop in the power of solar batteries after the encounter with the comet was the same 45%, this did not prevent two more sessions of studying the comet on departure - on March 10 and 11. As a result of the study of Halley's comet by the Soviet automatic stations Vega-1 and Vega-2, unique scientific results were obtained, including about 1,500 images. For the first time, spacecraft passed at such a close distance from a comet. For the first time managed to look at close range at one of the most mysterious bodies in the solar system. However, this was not the only contribution made by the Vega-1 and Vega-2 stations to the international program for the study of Halley's comet.
During the flight of the stations, up to their closest approach to the comet, interferometric measurements were carried out within the framework of the Pilot project. This made it possible to conduct the West European interplanetary station "Giotto" at a distance of 605 km from the comet's nucleus. True, already at a distance of 1200 km as a result of a collision with a cometary fragment at the station, the television camera went out of order, and the station itself lost its orientation. Nevertheless, Western European scientists managed to obtain unique scientific information.
The two Japanese interplanetary stations "Susi" and "Sakigake" also contributed to the study of Halley's comet. The first of them flew by Halley's comet on March 8 at a distance of 150 thousand km, and the second passed on March 10 at a distance of 7 million km.
The brilliant results of the study of Halley's comet by the automatic interplanetary stations "Vega-1", "Vega-2", "Giotto", "Susi" and "Sakigake" caused a wide international public outcry. 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 passage of Halley's comet, they continued their flight in heliocentric orbit, simultaneously exploring the meteor showers of comets Deining-Fujikawa, Bisla, Blanpane and all the same Halley's comet. The last communication session with the Vega-1 station was held on January 30, 1987. It recorded the complete consumption of nitrogen in gas cylinders. Station "Vega-2" lasted longer. The last session in which the crews were on board was held on March 24, 1987.
