Vega program

• 1. Introduction

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  The Vega program launched two spacecraft toward Venus in December 1984, carrying a secret tucked inside each one: a balloon. Not a scientific metaphor, but an actual helium-filled sphere, 3.54 meters across, designed to float through the cloud layers of another planet. When those balloons finally inflated and steadied themselves at 54 kilometers above Venus, they became the first human-made aircraft to fly anywhere other than Earth. That record would stand for decades, until NASA's Ingenuity helicopter lifted off from Mars in 2021.

  But Venus was only half the story. The same two spacecraft were also aimed at Halley's Comet, catching the comet during its 1985-1986 perihelion pass through the inner solar system. The name Vega was itself a clue: a contraction of Venera and Gallei, the Russian words for Venus and Halley, welded together into a single word for a mission that served two masters at once.

  How did the Soviet Union pull off a dual planetary encounter, and why did a canceled American mission help make it possible? Those are the questions this documentary will answer.

• 2. A Name Born of Cancellation

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  The American Halley mission was canceled in 1981, and that cancellation changed the course of Soviet planetary science. At the time, the Soviet Union was running the Venera program, a long-running series of Venus probes. With no American competitor heading for the comet, Soviet planners saw an opening. They redirected a future Venera mission toward Halley's Comet, and then reduced the Venus-side science on one of the spacecraft to make room for the new objective.

  The spacecraft design was rooted in two earlier missions: Venera 9 and Venera 10. Rather than building from scratch, engineers at the Babakin Space Center adapted what already worked. The craft were constructed by Lavochkin at Khimki, and they weighed 4,920 kilograms each. A Proton 8K82K rocket carried each one out of Baikonur Cosmodrome in the Kazakh SSR, the first launching on the 15th of December 1984 and the second on the 21st of December 1984.

  The project was not a solo Soviet effort. Austria, Bulgaria, France, Hungary, the German Democratic Republic, Poland, Czechoslovakia, and the Federal Republic of Germany all contributed. That coalition of countries, spanning both sides of the Cold War divide, helped make the mission's instruments broader and its data richer than any single nation could have managed alone.

• 3. Inside the Cloud Layer

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  At 54 kilometers above the Venusian surface, the pressure and temperature of the atmosphere match conditions on Earth at roughly 18,000 feet above sea level. That narrow band of relative familiarity was where the Vega balloon probes were designed to live. The planet's winds at that altitude move at hurricane velocity, and the carbon dioxide atmosphere carries sulfuric acid along with smaller concentrations of hydrochloric and hydrofluoric acid. To survive, the balloon envelopes were coated with polytetrafluoroethylene.

  Each balloon was a spherical superpressure type, 3.54 meters in diameter, filled with helium. A gondola assembly 1.3 meters long and weighing 6.9 kilograms hung below on a 13-meter tether. The total mass of the whole assembly was 21 kilograms. Power came from batteries designed to last 60 hours, though both balloons ultimately transmitted for more than 46 hours before contact was lost.

  The transmitter on board put out only 5 watts, limiting the data rate to 2,048 bits per second. Engineers used data compression to extract more information from that narrow channel, though even so, most instruments could only sample once every 75 seconds. Two networks of ground stations tracked the balloons: a Soviet network coordinated by the Soviet Academy of Sciences, and an international network coordinated by France's Centre national d'etudes spatiales. Between them, the two networks used 20 radio telescopes.

  The balloons were pulled from the landers at 180,000 feet above the planet's night side and fell to 164,000 feet while inflating before rising to a stable 177,000 feet. As they drifted from the night side to the daylight side, their tracking data revealed something unexpected: a vertical component to their motion, indicating up-and-down movement of air masses that no earlier Venus probe had detected.

• 4. What the Landers Found

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  Vega 2's lander touched down at 03:00:50 Universal Time on the 15th of June 1985, settling into eastern Aphrodite Terra at coordinates 8.5 degrees south, 164.5 degrees east. The touchdown site sat 0.1 kilometers above the planetary mean radius. At the surface, the lander measured a pressure of 91 atmospheres and a temperature of 736 Kelvin. A surface sample came back identified as anorthosite-troctolite, a rock type more commonly associated with the ancient crust of the Moon. The lander transmitted data from that scorching surface for 56 minutes.

  Vega 1's lander did not fare as well below. At 20 kilometers above the surface, a particularly hard gust of wind jolted the spacecraft and inadvertently activated the surface experiments early. By the time the lander actually touched down at 7.5 degrees north, 177.7 degrees east, those instruments had already exhausted themselves. The surface science from Vega 1 was lost.

  Both descent units were 1,500-kilogram spheres 240 centimeters in diameter. They were released several days before each spacecraft reached Venus and entered the atmosphere without active maneuvering. The instrument suites included temperature and pressure sensors, an ultraviolet spectrometer, a gas-phase chromatograph, an X-ray spectrometer, a mass spectrometer, and a drill-based surface sampling device.

• 5. The Halley Encounter

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  After releasing their Venus payloads, the two Vega motherships used Venus's gravity to bend their trajectories outward, redirecting themselves toward Comet Halley. Vega 1 made its closest approach on the 6th of March 1986, passing roughly 8,890 kilometers from the nucleus. Three days later, on the 9th of March, Vega 2 came within 8,030 kilometers.

  The examination of the comet was intense but brief: only the three hours around closest approach yielded the most detailed data. Scientists wanted measurements of the nucleus's dimensions, shape, temperature, and surface properties, as well as the structure of the surrounding coma and the interaction between the comet and the solar wind. The dust streaming off the comet was a particular concern, which is why each spacecraft carried a dual bumper shield for protection.

  Vega 1 and Vega 2 together returned about 1,500 images of Halley's Comet. The imaging system was itself a product of international cooperation, built by scientific and industrial teams from the Soviet Union, Hungary, France, and Czechoslovakia. Image processing was done at the IKI institute using a system built around a PDP-11/40 compatible computer. Scientists from the United States and East Germany joined their Soviet, Hungarian, French, and Czechoslovak colleagues in working through that data.

  The Vega probes were part of a larger group of spacecraft studying the comet, known as the Halley Armada. Spacecraft operations were discontinued a few weeks after the Halley encounters. Today, Vega 1 and Vega 2 travel in heliocentric orbits, carrying no further mission beyond their trajectory through the solar system.