On this day in (engineering) history…

October 22, 1975 - The Soviet unmanned space mission Venera 9 lands on Venus.

A hot, overcast, though reasonably bright, October day. The sulphuric acid clouds are so thick the Sun casts no shadows. Don't worry about sulphuric acid rain because surface temperatures of 485°C (the hottest in the Solar System and easily hot enough to melt lead) evaporate it long before a drop hits the ground. All of this contained in an atmosphere thick enough to crush a submarine.

This is Venus, where the Soviet Venera 9 probe is about to land.

Cloud system on Venus, captured using ultra-violet observation. Source: Wikimedia Commons

A hot planet in the Cold War

During the Cold War, the Space Race became one of many substitutes for hot superpower confrontation. In the 1960s and early 70s, both attempted to put probes into orbit around Mars and a lander on its surface.

The Soviet Union also paid attention to Venus, where it would send orbiters and landers between 1961 and 1984.

Venera 7 ('Venera' - Russian: Вене́ра, pronounced [vʲɪˈnʲɛrə] 'Venus'), in 1970, would be the first probe to land on another planet and send data back to Earth. The USSR's first fully successful Venus mission would be Venera 8, which landed, returned data to Earth, and lasted a full 50 minutes before being consumed by the ferocious Venusian atmosphere.

Until 1974, the Soviets had had little success with their Mars missions; even if the probes survived to return worthwhile data, none of these could be called 'successful.' It was becoming clear that American resources and technological capability far outmatched the USSR. In the mid-1970s, Roald Segdeev, director of the Soviet Space Research Institute, decided to abandon the exploration of Mars and pay closer attention to Venus.

Venus v Mars

Sending a probe to Venus has advantages over sending one to Mars. With a shorter journey, the unreliability of the avionics became less of an issue. Shorter journeys also meant the improving Proton rockets could lift a heavier payload – meaning a larger vehicle with more redundant systems - for a journey to Venus than for Mars.

While it was no secret that Venus was closer to hell than heaven, nobody knew what it looked like. This set the stage for Venera 9.

Replica of Venera 9, displayed at the K. E. Tsiolkovsky Museum of the History of Cosmonautics.
Source: Wikimedia Commons 

The probe

Venera 9 (and Venera 10, its sister probe) stood at a height of 2.8 metres.

The central, 1-metre-high portion had a diameter of 1.1 metres, with engine fuel tanks. The main instrument compartment had a 2.5-metre diameter. Its 'wingspan' - in reality, a pair of 1.25 by 2.1-metre solar panels mounted on either side of the vehicle – measured 6.7-metres across.

The high energy levels from the Sun within the inner solar system meant Venera 9 would require smaller than usual PV panels. The increased heat of the region made it necessary to equip Venera 9 with an extensive cooling system and a pipe network inside the lander.

Alexei Isaev's KB KhIMMash design bureau designed and produced the vehicle's KRD-425A engine, designed to fire seven times during the Earth to Venus transit and the insertion into orbit around the planet.

Descent into Hell

Placed atop a Proton-K/D rocket, Venera 9 blasted off from launch Site 81, platform 24 at the Baikonur Cosmodrome on June 8, 1975. The spacecraft had two parts: an orbiter - the first machine to orbit Venus - which carried instruments to measure the planet's cloud system and atmospheric parameters, and a lander - the first machine to send back photographs of another planet - and relay its data back to Earth.

Venera 9 reached Venus' orbit on October 20, 1975, when the lander, hidden within a hemispherical aeroshell, was released for its voyage to the surface. After an initial orbit, it began its descent at 125 kilometres altitude, at a velocity of 10.7 kilometres per second. After releasing the first parachute 65 kilometres above the surface, aerodynamic braking slowed it to 250 metres per second, when Venera jettisoned the top of the protective shell. The lander now slowed to 50 metres per second.

After the brake chutes opened, the lander began transmitting its data. At 62 kilometres altitude and a speed of 50 metres per second, the three main chutes open to further slow the lander. At this point, Venera ditched the lower half of the protective shield. Its descent continued for another 20 minutes before it threw off the main parachutes and continued its free fall to the surface, this time slowed by a disk-shaped aerobrake.

By now, the atmospheric density played a massive role in slowing the lander's descent velocity. When it struck the surface, the lander's speed had reduced to seven metres per second. After a descent lasting one hour and ten minutes, a ring-shaped inflatable device - which released pressurised gas as it hit the ground - cushioned the actual landing.

Venera: The Incredible Probe that the Soviets Sent to Venus

The mission

The lander came to rest on the side of a hill with a 20° slope and an extra tilt of up to 15° at an altitude of 2,500 metres above the planet's determined 'sea level.' The site, which could be in the Aikhylu Chasma tectonic rift valley, is situated at 31.01°N 291.64°E, in a highland area called Beta Regio.

The machine arrived on the planet equipped with two cameras mounted in pods either side of the main body. They would have produced a 360° panorama of the surface up to the horizon. An age-old photographic problem struck one of these cameras when a lens cap refused to be shaken off.

The very first image of Venus’ surface. Sent by Venera 9, October 22, 1975. Source: Wikimedia Commons

Consequently, we are left with a single image of a relatively flat landscape strewn with flat, sharp, slab-like basalt rocks, suggesting a slow erosion process or recent volcanic or tectonic activity in the area.

It measured a surface temperature of 485°C with an atmospheric pressure of 9,100 kilopascals or 90 atmospheres.

The thickness of the Venusian clouds means the surface receives an equivalent of 10% of the Sun's light, or a brightness of 14,000 lux, compared with Earth. Measurements point to 100 watts per square metre of solar radiation reaching the ground. Despite the thick cloud haze, visibility was approximately 100 metres, giving a surprisingly clear view of the surroundings. A Soviet scientist likened the conditions to an overcast day in Moscow.

Fate

The orbiter was able to transmit all the data it received to Earth. Making the mission a resounding success. Eventually, the Venera 9 lander fell silent, albeit not because it burned out. Approximately 53 minutes after the lander touched Venus's surface, the orbiter's trajectory took it out of radio distance. How long the lander remained 'alive' in those harsh conditions is unknown.

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By Stephen Phillips - IET Content Producer, with passions for history, engineering, tech and the sciences.