During the first quarter of a century of the Space Age, Venus had been a target of intense interest to Soviet space planners. Being the closest planet to our own, relatively large payloads could be launched towards Venus every 19 months with transit times that were about half that required to reach the next most distant planet, Mars. Starting with the launch of Venera 1 in 1961 (see “Venera 1: The First Venus Mission Attempt“), the Soviet Union had attempted to dispatch spacecraft to flyby or land on Venus during every available launch window throughout the 1960s. While the earliest attempts were thwarted by launch vehicle and spacecraft malfunctions, in October 1967 Venera 4 finally managed to reach our sister world and deploy a lander which, unfortunately, was crushed at an altitude of about 26 kilometers while returning data during descent because the atmosphere of Venus proved to be several times denser than anticipated (see “Venera 4: Probing the Atmosphere of Venus“).

After building and launching two successive batches of increasingly robust landers, Venera 7 finally landed on the surface of Venus on December 15, 1970 (the first successful landing on the surface of another planet) and managed to return basic information on its dense atmosphere. This feat was repeated by Venera 8 in July 1972 which also returned data on the properties of the surface for the first time as well. But with the completion of this mission, the limits of the first-generation Venera spacecraft design had been reached.

A New Generation

More ambitious missions to Venus would require a significantly larger spacecraft. The Soviet Union skipped the 1973 Venus launch window as a new and much more capable spacecraft was developed. Like all of the Soviet Union’s lunar and planetary spacecraft launched after 1965, the new second-generation Venera spacecraft was designed and built at NPO Lavochkin headed by Georgi Babakin until his death in 1971 when Sergei Kryukov took charge as the bureau’s General Designer. As a starting point of what was officially designated the 4V-1 spacecraft, the engineers at NPO Lavochkin decided to adapt the spacecraft originally developed for the M-71 and M-73 missions to Mars. Although the Mars 2 through 6 spacecraft of the early 1970s had experienced a series of issues that prevented any fully successful missions, their advanced design was highly adaptable and capable. And with the various hardware, software and quality control issues uncovered and resolved in the wake of the Mars missions, there was a much higher chance of success than if a totally new spacecraft were developed.

The new 4V-1 spacecraft were five times more massive than the metric ton-class first generation Venera spacecraft and would use the Proton-K fitted with a Blok D escape stage as a launch vehicle – the Soviet Union’s most powerful operational rocket. Like the earlier lander-laden Mars spacecraft, the 4V-1 would consist of two sections: an orbiter and a descent capsule holding the actual lander. The orbiter, like the M-71 and M-73 designs, consisted of a cylindrical core with a toroidal instrument module around its base. The 1.1-meter in diameter cylindrical structure housed propellant tanks holding about 1.1 metric tons of UDMH (unsymmetrical dimethyl hydrazine) and nitrogen tetroxide for the KTDU-425A engine used for orbit insertion and course corrections. This section had a diameter that was 0.7 meters narrower and was about one meter shorter than the version used on the Mars missions. The KTDU-425A engine, which was gimballed for attitude control and could be throttled to generate 9.9 to 18.9 kilonewtons of thrust, was mounted to point down from the base of the spacecraft and through the center of the instrument module. The total height of the orbiter was 2.8 meters.

Mounted on the cylindrical section were a pair of 1.25 by 2.1 meter solar panels with a total span of 6.7 meters. The structure for the solar panels also supported radiators for thermal control and a system of cold gas attitude control jets. Also mounted on this section was a 1.6-meter in diameter parabolic high gain antenna and six helical low gain antennas for communicating with the Earth and receiving data from the lander during its descent and after it reached the surface. Using the orbiter to record then replay the data from the lander allowed a data transmission rate of 256 bits per second compared to the rate of only one bit per second possible with Venera 8 which transmitted its data directly to Earth. Mounted on various points on the spacecraft were an impressive array of instruments to study Venus and the environment of the surrounding space. Among these instruments were a pair of panoramic telephotometers based on a design successfully employed by the Mars 4 and 5 orbiters which would image the Venusian cloud deck at violet and near-ultraviolet wavelengths with a resolution on the order of 6 to 30 kilometers.

Around the base of the 4V-1 orbiter was a 2.35-meter in diameter instrument module which contained the spacecraft’s computers, avionics, scientific instrument electronics and other sensitive equipment. This toroidal module, whose shape was chosen to minimize the length of required cabling and allow easier access to its systems during construction and testing, was pressurized to provide a laboratory-like environment for its equipment. This approach added to spacecraft mass but it simplified the design and testing of the systems as well as provided for easier thermal control. Various optical sensors were mounted on the exterior of the equipment section to provide inputs to a sophisticated autonomous navigation system.

Mounted on top of the orbiter was the 1,560-kilogram descent capsule. Given the markedly different conditions on Venus compared to Mars, this was a completely new design that would have to withstand a typical atmospheric pressure of 90 bars (where one bar is roughly equivalent to Earth’s atmospheric surface pressure) and temperatures of 470° C. The descent capsule consisted of spherical aeroshell coated with ablative material to survive the initial 10.7 kilometer per second entry into the Venusian atmosphere after it had been deployed by the orbiter. Once the worse of the entry into the atmosphere was completed, a series of parachutes would deploy to stabilize and slow the descending capsule then extract the actual lander. The 660-kilogram lander was built around a 0.8-meter in diameter, double-walled titanium pressure vessel that contained most of the lander’s systems. Precooling the lander before deployment, layers of insulation and heat absorbing material helped to keep the interior temperatures down so that the lander could withstand the 75-minute descent through the dense atmosphere of Venus and then survive for a minimum of 30 minutes on the surface.

While the first 20 minutes of the descent after the initial entry into the atmosphere employed a system of parachutes, these were cut loose at an altitude of 50 kilometers to hasten the descent through the increasingly dense atmosphere. For the rest of the trip to the surface, the lander would be slowed and stabilized by a 2.1-meter in diameter disk-shaped aerobrake near the top of the vehicle. After a free fall of 55 minutes, the lander would reach the surface at a speed of 7 meters per second (comparable to the speed from a 2.5 meter drop on the Earth) with the impact of landing cushioned by a shock absorbing ring at the base which also served to keep the lander upright. The two-meter tall lander was topped by a helical antenna which it used to transmit data back to Earth using the orbiter (which would have entered orbit around Venus just before entry) as a relay.

The 4V-1 Venera lander carried an array of instruments to study the atmospheric composition and structure as well as the optical properties of the clouds of Venus during descent. Once on the surface, an anemometer would measure wind speeds, a gamma ray densitometer would study the surface material while a gamma ray spectrometer would measure the concentration of radioactive elements like uranium, thorium and potassium to assess the types of rocks present at the landing site.

By far the most interesting instrument carried by the landers were a pair of 5.8-kilogram panoramic telephotometers mounted on opposite sides of the pressure vessel at a height of 0.9 meters. Similar in design to those carried by earlier Soviet Moon and Mars landers, these telephotometers would provide a pair of 512 by 128-pixel, 6-bit black and white images of the surface of Venus – the first images ever from the surface of another planet. These cameras were canted 50° downward so that their 40° by 160° panoramas would include the surface at the foot of the lander out to the horizon. Because surface illumination measurements made by Venera 8 indicated fairly low light levels, floodlights were mounted to the landing ring struts to ensure enough light was available for imaging. The pair of 4V-1 orbiters and landers would be the heaviest and most advanced spacecraft ever launched on a planetary mission up to that time.

Getting to Venus

The first of the new Venera spacecraft, the 4,936-kilogram 4V-1 No. 660, lifted off from the Launch Complex 81/24 in the Baikonur Cosmodrome in Soviet Kazakhstan at 2:37 UT on June 8, 1975. After a short coast in a 171 by 196-kilometer parking orbit with an inclination of 51.54°, the Proton’s Blok D escape stage reignited to send what was now designated Venera 9 on its way to Venus. Venera 9 made a 12.5 meter per second course correction using its KTDU-425A propulsion system on June 16 to refine its trajectory.

The second Venera probe, 4V-1 No. 661, lifted off at 2:20 UT on June 14, 1975 and into a temporary 162 by 206-kilometer parking orbit. With a mass of 5,033 kilograms, this spacecraft was slightly heavier than its predecessor primarily because it carried an extra 66 kilograms of propellant for orbit insertion from its slightly faster approach to Venus. In fact, this would be the heaviest planetary spacecraft ever launched until the Venera 15 radar mapper was sent to Venus in 1983. Once again, the Blok D escape stage fired as intended to send what was now called Venera 10 towards Venus. Like its sister spacecraft, Venera 10 made a minor course correction of 14.5 meters per second to adjust its trajectory on June 21.

After an uneventful four-month cruise, the pair of Venera spacecraft were finally approaching their target. On October 15, 1975, Venera 9 performed a 13.5 meter per second course correction to fine tune its trajectory a week before its encounter. The orbiter then fully charged the lander’s batteries and prechilled its interior to -10° C before releasing the descent capsule on a course for the day side of Venus. Shortly afterwards, the now lightened orbiter performed a 247.3 meter per second deflection burn to adjust its course to the opposite side of Venus. On October 22, as its descent capsule was still speeding towards its encounter, the Venera 9 orbiter fired its KTDU-425A engine for a 922.7 meter per second braking burn to enter an initial 1,500 by 111,700-kilometer orbit around Venus with an inclination of 34.17° to become the first spacecraft to enter orbit around Venus. After orbit insertion, the orbiter turned to receive and record the data from its lander.

At 3:58 UT on October 22, the Venera 9 lander hit the atmosphere of Venus at a speed of 10.7 kilometers per second at an angle of 20.5° to the local horizontal. About 14 seconds later, the loads had slackened from a peak of around 170 G to only 2 G and a 2.8 meter drogue chute was deployed at an altitude of 65 kilometers. The spherical aeroshell then split with the lower half allowed to drop away at the same time a larger 4.4 meter metallic parachute was deployed. After 11 seconds with the speed now down to 50 meters per second at an altitude of 60 to 62 kilometers, the upper half of the aeroshell released the lander which then deployed a trio of 4.3-meter parachutes. The lander continued transmitting data as it descended and finally cut its parachutes loose at an altitude of 50 kilometers to freefall the rest of the way to the surface.

Venera 9 finally landed on the surface of Venus at 5:13 UT at 31.01°N 291.64°E about 2,500 meters above the planet’s defined “sea level” in the northeastern part of the highland region known as Beta Regio. Immediately the lander began making measurements continuously cycling through its various instruments and transmitting the findings to the orbiter far overhead. The surface pressure was found to be 85 bars with a temperature of 455°C and a wind speed of just 0.4 to 0.7 meters per second. On board photometer readings indicated that a cloud of dust had been kicked up by the landing which quickly cleared.

The lander’s telephotometers immediately started continuous scans of the surroundings with the transmissions interspersed with other data. Disappointingly, the cover on one of the telephotometers failed to eject as planned but the other worked as intended to return data. It was immediately obvious that with the Sun 54° above the horizon, there was ample light available for imaging with the lighting level compared to that of a cloudy day in Moscow. The much gloomier conditions encountered by Venera 8 in 1972 were measured when the Sun was only 5° above the horizon so the floodlights did not prove to be needed after all. Measurements from the images, which provided a view of the horizon, and from a tilt meter on the lander showed that Venera 9 had come down on the side of a hill with a slope of 15° to 20° and that the lander itself was tilted an additional 10° to 15° by the uneven surface.

Surprisingly, the images returned by Venera 9 showed a landscape filled with angular rocks with little signs of dust or erosion. It was obvious that this was young mountainous terrain of a geologically active landscape. Measurements of the rock density and composition indicated that they were a type of basalt – the most common rock type on the Earth as well as the other rocky bodies of the inner Solar System. This contrasted with the findings of Venera 8 which hinted at a more granite-like composition at its landing site in Navka Planitia about 6,300 kilometers to the southeast. Venera 9 continued transmitting from the surface until the orbiter moved out of range 53 minutes after landing with the lander’s interior temperature reaching 60° C. The orbiter then turned towards the Earth and transmitted the recorded lander data to waiting Soviet scientists and engineers. Despite the problem with one of the telephotometers, the lander mission proved to be a resounding success.

As the Venera 9 orbiter continued on in orbit, its sister was fast approaching Venus to repeat its predecessor’s feat. Venera 10 made a final course correction of 9.7 meters per second on October 18, 1975 and released its descent capsule five days later. The orbiter then performed a 242.2 meter per second deflection burn to set itself on course for entering orbit around Venus. On October 25, the Venera 10 orbiter performed a 976.5 meter per second braking maneuver to enter an initial 1,400 by 114,000-kilometer orbit with an inclination of 29.50°.

At 4:02 UT, the Venera 10 descent capsule entered the atmosphere at an angle of 23°. Six seconds later, the peak deceleration reached 168 G as the outside temperatures soared to 12,000° C. As the lander slowed, the descent sequence then proceeded much as that of Venera 9. Venera 10 finally landed at 5:17 UT at 15.42° N 291.51° E in the border area between Beta and Hyndla Regio about 2,200 kilometers to the south of Venera 9. The atmospheric surface conditions were found to be similar to those at the previous landing site: an atmospheric pressure of 91 bars, a temperature of 464° C and light winds of 0.8 to 1.3 meters per second.

Unfortunately, the Venera 10 lander experienced the same failure as its sister with the cover on one of the telephotometers failing to be ejected after touchdown. The remaining telephotometer did function and sent back a series of panoramas that indicated a very different type of terrain at the new landing site. The Venera 10 lander touched down on a rolling plain with low outcrops of bedrock interspersed with weathered granular material visible to the horizon. The lander itself had come down on a three-meter slab that tilted the lander back about 8°. Although the analysis of the rocks present indicated a basaltic composition with an albedo of about 0.06 similar to that observed by Venera 9, this was obviously a much older and eroded landscape. The Venera 10 lander continued transmitting data for 65 minutes when its orbiting relay finally moved out of range.

The Orbiter Missions

With two successful landings on Venus and valuable images as well as other data in hand, the pair of Venera orbiters continued to study Venus from above. Venera 9 eventually trimmed its orbit to 1,510 by 112,200 kilometers with a period of 48 hours and 18 minutes and an inclination of 34.15°. Likewise, the Venera 10 orbiter tweaked its initial path around Venus and into a 1,620 by 113,900 kilometer orbit with an inclination of 29.5° and a period of 49 hours and 23 minutes. From these orbits they began their own long term study of Venus.

By November 5, 1975 the imaging systems carried by the Venera 9 and 10 orbiters had secured seven and five images, respectively, of the clouds of Venus in violet and ultraviolet wavelengths. By the end of 1975, Venera 9 had returned a total of 17 such images with resolution as good as 6.5 kilometers. The other instruments on board studied the properties of the clouds with the data suggesting for the first time the presence of three distinct cloud layers. Other instruments studied the hydrogen corona of Venus and the planet’s near space environment. It was found that even though Venus had no intrinsic magnetic field, the interaction of the solar wind directly with the planet’s ionosphere created a magnetic plasma tail.

During their missions, the orbiters were also used for bistatic radar investigations of the Venusian surface at a wavelength of 32 centimeters. Using transmissions from the orbiters received by equipment back on the Earth, 55 strips up to 200 kilometers wide and 1,200 kilometers long were observed. While initial analysis of these data yielded simple one-dimensional topographic profiles with ground resolution of 20 to 80 kilometers, later analysis of the Venera 10 orbiter data produced two-dimensional images for five small regions with a resolution of 5 to 20 kilometers – comparable to the resolution of Earth-based radar images of the time.

Both orbiters continued to make observations of Venus until transmitter failures silenced them both about three months after entering orbit. The missions were declared officially completed on March 26, 1976. Although they might not have functioned as long as some might have hoped, the Venera 9 and 10 orbiters provided the first long term observations of Venus and its surroundings instead of the brief snapshots delivered by the previous brief encounters by earlier American and Soviet Venus missions. Combined with the accomplishments of the landers, the Venera 9 and 10 missions were clearly the most successful planetary missions flown by the Soviet Union to date providing valuable data on our sister planet as well as propaganda just as the American Viking missions to land on Mars got underway.

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Related Video

Here is a brief Russian-language documentary on the Venera 9 and 10 missions.

Related Reading

“The Mars Orbiter That Almost Was Not”, Drew Ex Machina, May 22, 2014 [Post]

“Venera 1: The First Venus Mission Attempt”, Drew Ex Machina, February 12, 2016 [Post]

“Venera 2 and 3: Touching the Face of Venus”, Drew Ex Machina, March 1, 2016 [Post]

“Venera 4: Probing the Atmosphere of Venus”, Drew Ex Machina, October 20, 2017 [Post]

General References

K.P. Florenskiy et al., “Panorama of Venera 9 and 10 Landing Sites”, in Venus (D.M. Hunten, L. Colin T.M. Donohue and V.I. Moroz, editors), pp. 137-153, University of Arizona Press, 1983

Brian Harvey, Russian Planetary Exploration: History, Development and Prospects, Springer-Praxis, 2007

Wesley Huntress, Jr. and Mikhail Ya. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer-Praxis, 2011

Nicholas L. Johnson, Handbook of Soviet Lunar and Planetary Exploration, Univelt, 1979

A.G. Pavelyev et al., “Reanalysis of Bistatic Radar Results: The Venus Surface and Lower Atmosphere”, Paper No. 2094, 47th Lunar & Planetary Science Conference, 2016

Andrew Wilson, Solar System Log, Jane’s Publishing, 1987