Vega 1 and Vega 2

Vega grew out of a Venus mission that was already under way. The Space Research Institute of the USSR Academy of Sciences (IKI) dates the start of work on the station it calls V-85 5VK to a decree of the Communist Party Central Committee and the Council of Ministers of 8 May 1980. Ballistic studies then showed that the carrier, once it had released its payload at Venus, could be bent by the planet's gravity onto a path through Comet Halley, which was due at perihelion on 9 February 1986. IKI credits the change largely to its director, Roald Sagdeev; Don P. Mitchell's history of the Soviet Venus programme credits the proposal to the astronomer V. G. Kurt, with the orbital analyst A. A. Sukhanov proving it could be flown. The earlier project was folded, IKI says, and the new one was named Vega, from the Russian Venera (Venus) and Gallei (Halley). The Russian State Archive of Scientific and Technical Documentation (RGANTD) holds the technical assignment for the complex, drawn up between May and September 1981 and finally approved by the minister of general machine building, S. A. Afanasyev, on 24 February 1982. The comet had a cost on the Venus side: the NASA Planetary Data System catalogue notes that larger French-led balloons had been considered in early planning, and that adding Halley forced the use of the smaller Soviet balloons that eventually flew.

Roald Sagdeev, a plasma physicist, ran IKI from 1973 to 1988, according to the institute's own history, and IKI names him scientific leader of the project, with V. M. Kovtunenko of NPO Lavochkin as chief designer. NPO Lavochkin adds that an International Scientific and Technical Committee headed by Sagdeev coordinated the scientific and industrial cooperation, which drew specialists from the USSR, West Germany, France, Austria, East Germany, Hungary, Poland, Czechoslovakia, Bulgaria and the United States. The 1986 Soviet overview of the Venus results (NASA translation TM-88516) puts him in general charge of the balloon science and V. L. Barsukov in charge of the lander programme. IKI lists him as a foreign member of the US National Academy of Sciences and the Royal Swedish Academy of Sciences. He was still commenting on spaceflight in 2026: the newspaper Metro interviewed him on 13 April, and IKI's weekly press digest listed it.

Each station, index 5VK, had two parts: a carrier, which Soviet documents call the flyby craft, and a descent sphere 2.4 m across. NPO Lavochkin gives the whole station 4,923.5 kg; RGANTD splits a rounded 4,923 kg into a 3,170 kg carrier and a 1,750 kg descent vehicle, and Asif Siddiqi's NASA chronicle Beyond Earth gives about 4,840 kg. Inside the sphere rode a lander and, in a ring-shaped container around the lander's antenna, a balloon probe that RGANTD puts at about 120 kg with its parachutes and helium system. The lander's own mass is where the sources split most widely: 740 kg on the surface for NPO Lavochkin, 680 kg for RGANTD and about 750 kg in the Planetary Data System catalogue. Because the carriers would cross the comet's dust at around 80 km/s, NPO Lavochkin fitted armour of two-layer, and in places three-layer, screens over their vital parts. The cameras and spectrometers rode on a steerable platform, ASP-G, which the Soviet encyclopedia yearbook for 1987 credits to Czechoslovakia and the USSR; photographs in IKI's anniversary archive show its parts being made at the VPZ Behovice works in Czechoslovakia.

Proton-K rockets with Blok D-1 upper stages launched Vega 1 from Baikonur on 15 December 1984 and Vega 2 on 21 December. The clock times, 09:16:24 and 09:13:52, come with a disputed time zone: IKI labels the Vega 1 time Moscow time, while Siddiqi and Jonathan McDowell's launch catalogue give the same figures as UT, three hours apart. In NPO Lavochkin's flight scheme each station left a parking orbit of 51.5 degrees and 87.6 minutes for Venus after about 1.3 hours. The cruise took 178 days for Vega 1 and 176 days for Vega 2. Two trajectory corrections aimed the descent spheres, and on the way the carriers measured interplanetary magnetic fields, solar and cosmic rays, X-rays, neutral gas and dust.

The comet dictated how the Venus half would be flown. Because of the flight geometry toward Halley, the 1986 report on the landers' ultraviolet spectrometers explains, both landing sites had to be on the night side, so the landers carried no cameras (Mitchell) and the spectrometer brought its own lamp instead of relying on sunlight. NPO Lavochkin lists the other constraints. The balloons had to enter on the half of the disc visible from Earth, so that radio telescopes could follow them, and as far as possible from the subsolar meridian, where conditions could end a balloon's flight early. The carrier had to aim a sphere that could not steer itself, stay out of the atmosphere, remain in radio contact while relaying the lander's data, and then fire its engine again after the flyby to reach the comet.

The Vega 1 descent sphere separated on 9 June 1985. NSSDCA puts its entry into the atmosphere at 01:59:49 UT on 11 June, at 10.75 km/s and an angle of 18.23 degrees. The same catalogue has a pilot parachute opening at 65 km, the upper hemisphere of the heat shield coming away with the balloon system, the lower one a few seconds later and the parachute released at 47 km; the 1986 Soviet table gives 63 km for the parachute opening and 46 km for its release, heights measured from a radius of 6,052 km. The lander then fell on a disc-shaped air brake, a descent the 1985 Soviet yearbook planned at about 65 minutes. The carrier passed Venus at 39,000 km, measured from the surface in the 1986 yearbook; NSSDCA and Siddiqi give the same figure without saying what it is measured from.

About 18 km above the ground the Vega 1 lander was jolted. NSSDCA describes a mechanical shock of unknown origin, possibly a jammed valve suddenly releasing, which triggered the accelerometer meant to sense touchdown; the drill of the soil X-ray spectrometer deployed in mid-air and was useless after landing. Mitchell adds that electrical impulses and Doppler fluctuations were recorded at the same moment, and he notes similar disturbances between 12 and 18 km on Venera 11 to 14 and on the four Pioneer Venus probes; writing in 2003 and 2004, he called the cause of this layer of trouble unknown. The lander touched down at 03:02:54 UT in Rusalka Planitia, the Mermaid Plain, and transmitted for 56 minutes according to NSSDCA and Siddiqi (Mitchell says about 20 minutes). Sagdeev's team reported 95 atm and 740 K at the site but footnoted that the Vega 1 temperature came from a model; Siddiqi gives 467 °C and 93.88 atm, and Mitchell says the lander's temperature and pressure unit malfunctioned, which fits the absence of any Vega 1 descent profile in NASA's archive. The rest of the lander worked. Its gamma-ray spectrometer measured 0.45 per cent potassium, 0.64 ppm uranium and 1.5 ppm thorium in the ground, each with a wide error bar in Mitchell's table, and Mitchell credits its Malakhit mass spectrometer, the only one of the pair to work, with finding sulfur trioxide and chlorine in cloud particles.

Vega 2 repeated the sequence four days later: separation on 13 June, entry at 01:59:30 UT on 15 June at 10.80 km/s and 19.08 degrees, and touchdown at 03:00:50 UT, which Siddiqi places about 1,500 km south-east of its twin (Mitchell says about 1,300 km; every source's own coordinate pair except NSSDCA's puts them about 1,480 to 1,680 km apart). Its carrier passed 24,500 km from the surface, according to the 1986 yearbook; NSSDCA gives no figure. The lander transmitted for 57 minutes (Siddiqi). Its temperature and pressure sensors produced the lander profile in NASA's Planetary Data System (the volume holds no Vega 1 lander file): 431 records prepared by Ralph Lorenz, running from 62.9 km down to the ground and ending at 89.06 bar and 734.3 K. The 1986 Soviet table gives 91 atm and 734 K, a temperature it marks as based on measured data, NSSDCA gives 736 K, and Siddiqi gives 462 °C and 87.11 atm.

This time the drill worked. A sample was bored out, passed through an airlock into the pressure hull and analysed by X-ray fluorescence for the rest of the lander's life. Yuri Surkov's team at the Vernadsky Institute of Geochemistry reported about 45.6 per cent silica, 16 per cent alumina, 11 per cent magnesium oxide (11.5 in the yearbook's table) and very little potassium or titanium, each with a wide error bar. What the rock is has been read in several ways. Surkov's 1986 paper matched it to the anorthosite-norite-troctolite group, which it describes as widespread on the lunar surface, and explained that the site had been chosen in north-eastern Aphrodite Terra precisely to sample Venus's high mountain regions; the 1986 encyclopedia yearbook, 'with some reservations', called it olivine gabbro-norite; NSSDCA and Siddiqi write anorthosite-troctolite. Magellan radar later changed the picture of the site itself. Mapping published in 2001 by A. M. Abdrakhimov, also of the Vernadsky Institute, found more than 99 per cent of the Vega 2 landing circle covered by wrinkle-ridged plains of mafic lava in southern Rusalka Planitia, and cited earlier work concluding that every Venera and Vega lander had sampled volcanic plains. By uranium, thorium and potassium, the yearbook put both sites' rocks 'close to terrestrial gabbroids'.

Several new lander experiments asked what the clouds are made of. The 1986 yearbook reports direct measurements of about 1 mg of sulfuric acid per cubic metre between 48 and 63 km, along with sulfur, chlorine and probably phosphorus, which it says was detected in the clouds for the first time. It describes the clouds as a thin fog by Earth standards, with particles concentrated in two layers 3 to 5 km thick near 50 and 58 km. The ultraviolet spectrometers, led by V. I. Moroz and the French researcher J. L. Bertaux, returned about 30 full spectra from 55 km to the ground on both landers. Mitchell says they found sulfur dioxide and possibly sulfur vapour; the team's first report, in 1986, found a broad absorption band whose shape did not match sulfur dioxide, tentatively credited it to free sulfur vapour and called the identification unresolved. Mitchell also reports that the aerosol counters found two populations of particle sizes and no sign of the large third population that the Pioneer Venus large probe had reported in 1978, a difference his account leaves open. The VM-4 hygrometers measured water vapour on the night side from 62 km down to 25 km.

The descent spheres also carried the balloon probes, which NPO Lavochkin describes as the first used as a research tool in world spaceflight; RGANTD says they drifted at 53 to 55 km for about two days each and covered more than 11,000 km. Two networks of radio telescopes followed them: a Soviet one coordinated by IKI and an international one coordinated by the French space agency CNES, with NASA's large antennas at its core. Their flights, tracks and results have their own page, The Vega balloons.

Two weeks after the Venus flybys the Vega Halley leg began. Trajectory corrections on 25 June for Vega 1 and 29 June 1985 for Vega 2 turned both carriers toward the comet, according to NPO Lavochkin. The navigation was unusually tight: Halley orbits the Sun in the opposite direction to the planets, so the meeting was head-on at about 80 km/s, and IKI calculates that a craft only one hour late after its 14 months of flight would have missed the meeting point by about 100,000 km. Vega 1 made a further correction on 10 February 1986 (Siddiqi). On 12 February controllers at the deep space centre in Yevpatoria commanded the Vega 1 scan platform out of its stowed position, and Vega 2's three days later; both then imaged Jupiter from about 800 million km to calibrate the cameras, the 1987 yearbook records.

Vega 1 took its first television pictures of the comet on 4 March from about 14 million km, looked again on 5 March from 7 million km, and flew past the nucleus on 6 March during a three-hour session. Siddiqi times closest approach at 07:20:06 UT at 8,889 km and 79.2 km/s. Other Russian figures for the distance are 8,879 km in NPO Lavochkin's 2024 anniversary article, 8,880 km at RGANTD and 8,890 km in the 1987 yearbook and on NPO Lavochkin's project page. Siddiqi says Vega 1 took more than 500 pictures and that dust battered it without disabling any instrument. The French infrared spectrometer IKS, built by the laboratories now called LESIA and IAS, worked nominally on this pass, according to CNES. It recorded water, carbon dioxide, carbon monoxide, formaldehyde and carbonyl sulfide, a strong band at 3 micrometres from carbon-hydrogen bonds in complex but unidentified organic molecules, and a broad silicate feature characteristic of olivine.

Its twin began the approach on 7 March, when controllers alternated sessions between the two craft and photographed the comet from the head and the tail almost at once, as the 1987 yearbook puts it. On 9 March Vega 2 passed the nucleus at 8,030 km at 07:20 UT and 76.8 km/s (Siddiqi); NPO Lavochkin's 2024 article gives 8,010 km and RGANTD 8,045 km. Its roughly 700 images were sharper than its twin's, partly because there was less dust outside the coma, but a fault in the primary pointing software overexposed many of them, and the craft lost 80 per cent of its power, against 40 per cent for Vega 1 (Siddiqi; Mitchell gives a 50 per cent loss of solar-panel power for the pair). Across the two carriers seven instruments were partly damaged and none was put out of action (Siddiqi). Vega 2 went on observing on 10 and 11 March. IKI's retrospective describes a trade-off behind the real-time design: the platform kept the comet in view while the craft stayed pointed at Earth, and data went straight home because dust might wreck a recorder; NSSDCA, by contrast, describes a 5-megabit tape recorder covering the plasma and dust instruments.

Soviet sources present the nucleus pictures as the first ever taken; the 1987 yearbook says they were 'obtained for the first time in the history of mankind'. ESA, for its part, credits Giotto with the first close-up images of a nucleus and the first view of its shape. The two craft together returned more than 1,500 images, about 70 of them of the nucleus (RGANTD; NPO Lavochkin's 2024 article says more than 1,000). The nucleus proved to be an irregular, dark body: 16 by 8 by 8 km in the 1987 yearbook and at RGANTD, about 15 by 7 by 7 km in IKI's 2016 retrospective, reflecting about 4 per cent of the light and turning once in 53 hours, according to the yearbook and RGANTD. It was 'losing about 40 tonnes of water per second', in IKI's words (the yearbook says about 40 tonnes of ices, mostly water and carbon dioxide), and about ten jets of gas and dust were seen during the Vega 2 pass (the yearbook; Mitchell counts at least five on the sunward side). The dust instruments found many grains containing hydrogen, carbon and oxygen, and the PUMA analyser measured a high ratio of carbon to silicon, with nitrogen alongside the carbon, which the yearbook read as a sign of complex organic matter. IKI adds two surprises from the ion measurements: iron ions near Vega 2's closest approach that optical spectra had not shown, and an unpredicted boundary, the cometopause, about 160,000 km out.

The Vegas also worked for another spacecraft. In the Pathfinder project, Lotsman in Russian, radio telescopes in different parts of the world fixed the positions of the two craft while their television images refined the comet's path; the 1987 yearbook, which describes the method, dates its end to 11 March and names organisations of the USSR, ESA and the United States. IKI says the data narrowed the nucleus position from about 1,500 km to 40 km. ESA describes the Vegas as pathfinders that passed close enough to locate the nucleus so that Giotto could home in on it, and the European probe passed within 596 km on 14 March 1986. CNES, describing the French instruments aboard, puts the same role simply: being first, the Vegas had to refine Giotto's trajectory. The Japanese probes Sakigake and Suisei and the American-European ICE completed the fleet that IKI lists for Halley's 1986 return.

After Halley both carriers went into orbit around the Sun and kept measuring the space around them. NPO Lavochkin records the last session with Vega 1 on 30 January 1987, when the nitrogen in its gas bottles was found to be completely spent. Vega 2 lasted longer, and its last session in which commands got through to the spacecraft was held on 24 March 1987. By then the project had been celebrated at home: on 18 March 1986 Mikhail Gorbachev received its leading scientists in the Kremlin, and NPO Lavochkin's general designer, V. M. Kovtunenko, the project's technical leader, was elected a corresponding member of the USSR Academy of Sciences after the mission.

In Mitchell's history Vega is the closing chapter of the Soviet Venus programme, whose last missions to the planet arrived in 1985. What the pair left there is poorly located. The two landers lie in Rusalka Planitia inside circles of probable error 150 km in radius, and at least five published coordinate pairs exist for each; the Vega 2 figure in NSSDCA's catalogue sits 1,400 to 1,750 km west of the others. The heat-shield hemispheres and parachutes also came down, at positions the sources read here do not give. The inventory of everything that reached the planet is on What we left at Venus, and the engineering of the descent on Landing on Venus.