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The Venera-7 mission On August 17, 1970, the Soviet Union launched Venera-7. It would become the first spacecraft to transmit data from another planet.
Venus, Earth's closest but mysterious planetary neighbor had become even more of an enigma as discoveries made by the early Soviet probes during the 1960s had shattered earlier beliefs that the similarly sized world was an "Earth-like" planet. Direct measurements left no hope for finding "warm oceans" on the planet's surface as it had been still believed just a decade earlier. The Venera-4 probe, launched in 1967 and designed to withstand around 10 atmospheres of pressure, had been obliterated at an altitude of around 26 kilometers by pressure that reached around 15 atmospheres. Designers at the Lavochkin bureau in Moscow, who were responsible for the development of Soviet planetary spacecraft, sent reinforced follow-up probes — Venera 5 and 6 in 1969. There were built to withstand up to 25 atmospheres which allowed them to descend as low as 19 kilometers before the atmospheric pressure destroyed them as well. The direct measurements conducted by Venera-5 and -6 at different regions of the planet down to an altitude of around 20 kilometers allowed scientists to extrapolate temperatures on the planet's surface at between 718 and 783K degrees and the pressure between 70 and 120 atmospheres. Obviously, not a drop of water could exist on the planet where 500-degree-Celsius surface temperatures were expected.
After carefully reviewing available data, in May 1969, the Lavochkin design bureau initiated work on the next set of Venus probes intended to withstand up to 180 atmospheres. To survive the landing, a pair of landers, designated V-70 based on the expected launch toward Venus in 1970, were each "packed" into the VT-6 titanium alloy shells, capable of retaining its mechanical properties under temperatures reaching 500C degrees. Huge external pressure dictated a shape as close to a sphere as possible. The welded structure was found to be unworkable, so the body of the capsule was fabricated from two hemispheres made by stamping.
Fabrication of the shell for the V-70 descent module. The extra protection came with a price -- the vehicles' mass exceeded the capabilities of their launchers by some 20 kilograms. In a frantic search to save weight, engineers decided to remove telemetry systems from the upper stage of the launch vehicles that would push each probe from initial Earth orbit on its way to Venus. "This way, we barely fit into the weight requirements," said Vladimir Perminov, deputy chief designer for deep-space spacecraft at Lavochkin bureau at the time. Each egg-shaped lander would then carry communication equipment and a multitude of sensors which would measure around two dozen factors during its descent, including external and internal temperature of the spacecraft, the pressure and the composition of atmospheric gases, etc. Each capsule was also equipped with a parachute, which would be deployed after the craft had completed its initial aerodynamic descent. The parachute was reduced in size, compared to the previous probes, in order to accelerate the landing. The Venera-7 mission
In August 1970, the two planetary missions lifted off toward Venus from Baikonur Cosmodrome: on August 17, at 08:38 Moscow Time, a Molniya booster successfully inserted the first probe — V-70 No. 630 — into an initial orbit around the Earth. The fourth stage ignited at 09:59 Moscow Time and fired for 244 seconds accelerating the vehicle to a velocity slightly higher than the second cosmic speed, according to the official TASS news agency. The announcement identified the spacecraft as Venera-7. (On Aug. 22, 1970, the second spacecraft — V-70 No. 631 — also reached parking orbit, but failed to enter a trans-Venusian trajectory and it was identified as Kosmos-359.) In December 1970, Venera-7 approached Venus after a rather uneventful flight. On December 15, the Venera-7 lander separated from its cruise stage and plunged into the planet's atmosphere on the dark side of the planet, which was facing Earth. To their horror, scientists on the ground discovered that due to malfunction of a mechanical switch on the probe, the spacecraft had lost the capability to transmit all but a single channel of data. "We were lucky, this switch stuck on a temperature reading," Perminov remembers, "Temperature data allows you to estimate pressure too, because they are related." As Venera-7 descended into the Venusian atmosphere, it continued transmitting temperature data down to an altitude of around 10 meters. Then another disaster struck. At this point, the probe's parachute was lost and the spacecraft plummeted toward the surface of Venus. The mission was seemingly over -- the Russian deep-space control station in Crimea was receiving nothing but background noise from the emptiness of space. More stunning was the news a week later, when experts from the Moscow's Institute of Radio Electronics told their colleagues from NPO Lavochkin that they had been able to discern Venera-7's signal from the background radio noise recorded after the landing. After deciphering a very weak signal, the scientists confirmed that for around 23 minutes after hitting the surface of another world, Venera-7, had continued transmitting temperature data. That was despite the fact it was laying on its side in darkness with its antennas pointed away from Earth. The hardy spacecraft had delivered the first measurements conducted directly on the surface of another planet. The data confirmed what has already been speculated about the "weather" on Venus -- the surface temperature was 237 to 246 degrees Celsius -- enough to melt such metals as lead or zinc. The atmospheric pressure at the surface turned out to be around 93 atmospheres, comparable to an ocean depth of 800 meters on Earth
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