Ask any serious space enthusiast about the exploration of Venus and the Soviet Venera missions immediately come to mind. During the 1970s and first half of the 1980s, the Soviet Union launched a dozen missions to our sister planet including eight which carried landers that survived the hellish surface conditions for up to an hour returning valuable data. These data included four sets of images which represent humanity’s only close up glimpses of the surface of Venus. Four orbiters performed long term studies of Venus and made the first kilometer-scale radar maps of most of Venus’ northern hemisphere.

As successful as these missions were, they came at a cost. A series of failed missions to Venus during the 1960s provided hard lessons on building launch vehicles and spacecraft that could not only survive the extreme and largely unknown conditions on the planet itself but also the three-month-plus transit from the Earth. Probably one of the more frustrating failures from this time were those of the Venera 2 and 3 missions launched over a half a century ago.

The Origins of the 3MV

What would become the Venera 2 and 3 missions can be traced back to the first attempts by the Soviet Union to reach Venus in February 1961 with the launch of a pair of 1VA spacecraft. The 1VA and its successors as well as its 8K78 rocket that launched them (better known as the “Molniya” after the Soviet communication satellite series that regularly used this rocket) were designed and built at OKB-1 led by the famous Soviet aerospace engineer, Chief Designer Sergei Korolev. One of these 1VA probes fell victim to a failure of its new 8K78 launch vehicle like the pair of 1M sister probes launched towards Mars the previous October (see “The First Mars Mission Attempts”). Only Venera 1 was successfully placed on course to Venus after its launch of February 12, 1961. Unfortunately the hastily built probe suffered a series of malfunctions and fell silent only a couple of weeks after getting underway (see “Venera 1: The First Venus Mission Attempt”).

With the next favorable launch windows to Mars and Venus in 1962 only months apart, the decision was made to launch a half-dozen spacecraft built to a common design called 2MV. A total of four variants of the 2MV were built with each tailored specifically to two different missions — flyby or landing — for two different targets: Venus or Mars. Unfortunately, all three of the 2MV-series spacecraft launched towards Venus in August and September of 1962 never made it beyond Earth orbit due to problems with the 8K78 rocket. Likewise, two of the 2MV spacecraft bound for Mars also succumbed to launch vehicle failures two months later. Only Mars 1 managed to survive launch and was sent on its way to Mars on November 1, 1962. Despite the promising start, a malfunction in the spacecraft’s attitude control system doomed the mission of Mars 1 to failure months before it ever reached its target (see “You Can’t Fail Unless Your Try: The Soviet Venus & Mars Missions of 1962“).

Even before the last transmission from Mars 1 had been received, the decision had already been made to send another half dozen spacecraft towards Venus and Mars during 1964 launch opportunities using an improved spacecraft design called 3MV. Like the earlier 2MV, the new 3.6-meter tall 3MV design consisted of two sections. The first, known as the orbital compartment, was a cylinder with a diameter of 1.1 meters that was about as tall. As was the usual Soviet practice, the interior of this compartment was pressurized with dry nitrogen to 1.1 atmospheres in order to simulate an Earth-like laboratory environment for the internal equipment. This approach increased the mass of the spacecraft but greatly simplified the thermal design and testing of the spacecraft’s systems. The equipment inside the orbital compartment included communications gear, power supplies and their associated batteries, automated control systems, data recorders, and some experiment electronics. Various Sun and star sensors were also mounted inside the orbital compartment and looked through a window to acquire and track their targets for attitude reference.

Attached to the top of the orbital compartment was a course correction system that employed a KDU-414 engine designed and built at OKB-2, led by Aleksei Isayev. The pressure-fed KDU-414 burned UMDH (unsymmetrical dimethylhydrazine) and nitric acid to generate two kilonewtons of thrust. Normally this engine would be employed twice during a typical mission: once a few days after leaving the Earth to correct the probe’s initial trajectory for ineviable launch errors, and a second time a few days before encountering its target to refine its approach to meet the mission’s objectives. Also located here was the attitude control system which used pressurized nitrogen stored in tanks mounted on the orbital compartment.

Attached to either side of the orbital compartment were a pair of solar panels with a total span of about 4 meters that generated power for the spacecraft. Attached to the ends of the solar panels were hemispherical radiators designed to provide thermal control for the spacecraft’s interior systems. Water pumped through heat exchangers in the interior would circulated out through black- or white-painted sections of the radiators to heat or cool the spacecraft systems as needed to maintain the interior’s temperature between 20°C and 30°C.

A two-meter in diameter high-gain directional antenna mounted on the anti-sun side of the orbital compartment was used for long distance communications. Various low gain antennas were also mounted on the exterior of the orbital compartment for an omni-directional communications capability using transmitters operating in three different frequency bands. Instrument sensors to measure magnetic fields, various types of radiation and micrometeoroids that were mounted on the exterior rounded out the orbital compartment.

The second pressurized section of the 3MV spacecraft was called the planetary compartment. Mounted on the bottom of the orbital compartment, the approximately one-meter tall planetary compartment held instruments to be used to study the target planet. As with the 2MV, the 3MV design had four design variants. The 3MV-1 carried a planetary compartment designed to land on Venus, while the 3MV-2 had instruments designed to study Venus during a close flyby. Likewise, the original 3MV-3 and 3MV-4 designs were meant to land and flyby Mars, respectively. Each model had a launch mass of about one metric ton, give or take, depending on the energy requirements for each planetary launch window. These spacecraft were much bigger and had much more ambitious objectives than NASA’s Mariner missions to Venus and Mars during this era.

While the 3MV incorporated many design improvements to address the problems uncovered in the 2MV spacecraft, Korolev and his engineers realized that test flights of the improved 3MV would be desirable to reveal any additional issues well before the launches to Venus and Mars in order to improve the chances of success. As a result, test flights of representative 3MV designs would be launched as part of a series known as “Zond” (Russian for “probe”). The 3MV-1A was a stripped down model of the Venus lander that was to be launched into a solar orbit which would bring it back to Earth after a flight of five to six months. The reentry into Earth’s atmosphere would approximate the conditions the 3MV-1 lander would encounter during a Venus landing. The second engineering model was a modified version of the Mars flyby spacecraft designated 3MV-4A. This spacecraft was to carry a planetary compartment equipped with an miniaturized film-based imaging system as well as other scientific instruments. After being launched into a simulated trajectory towards the orbit of Mars, the 3MV-4A would turn its camera back towards the receding Earth at a distance of 40,000 to 200,000 kilometers and acquire a sequence of photographs that would subsequently be developed automatically on board. The spacecraft would then transmit its scanned photographs and other data gathered on the interplanetary environment out to distances as great as 200 to 300 million kilometers as part of a long distance communications test.

The launch vehicle for the 3MV was the four-stage 8K78 Molniya. The first three stages of this rocket would eventually serve as the basis of the Soyuz launch vehicle still in use today. The first two stages of the 8K78 consisted of the Blok A core surrounded by four tapered boosters designated Blok B, V, G, and D. The engines of the four boosters and core would ignite on the launch pad to generate 4,054 kilonewtons of thrust. After two minutes of flight, the four boosters would shut down and separate from the rising rocket. After another 175 seconds of flight, the Blok A core would exhaust its propellants leaving the Blok I third stage to take over. The Blok I would burn for four minutes to place the 3MV payload and its Blok L escape stage into a temporary Earth parking orbit. After a short coast in orbit, the Blok L escape stage would ignite to send the 3MV towards its planetary target. The 8K78 was 42.1 meters tall and had a liftoff mass of about 306 metric tons. Before the first orbital test flight of the American Block II Saturn I rocket in January 1964, the 8K78 was the most powerful rocket in the world (see “The Largest Launch Vehicles Through History“).

The First 3MV Missions

On March 21, 1963, the Soviet government officially approved the 3MV program. It would consist of two 3MV-1A flights and a single 3MV-4A flight to be launched in 1963, as well as a total of six operational 3MV spacecraft to be launched to Venus and Mars. Inevitable problems during the construction and testing of the new 3MV spacecraft delayed the launch of the engineering test flights and eventually forced the Venus mission to be scaled back to just a pair of 3MV-1 landers. The first 3MV-1A launch attempt in November 1963 failed as did the second on February 19, 1964 which had been delayed so long, it was launched towards Venus during the earliest part of that year’s window in hopes of getting a few weeks of vital engineering data (see “Trajectory Analysis of Soviet 1964 Venus Missions”). Without the benefit of an engineering test flight, the pair of 3MV-1 landers lifted off using the improved 8K78M rocket. Unfortunately only the one 3MV-1 lander managed to survive launch on April 2, 1964, and was sent on its way to Venus. But as had happened with earlier Soviet planetary missions, problems were detected during the first communication session so instead of being called “Venera 2”, the troubled probe received the generic designation “Zond 1”. Zond 1 eventually fell victim to a growing list of problems during its flight despite its design improvements and fell silent two months before its encounter with Venus (see “The Soviet Zond Missions of 1963-65: Planetary Probe Test Flights“).

With this latest failure, the launch of the 3MV-4A Zond test flight, which had been scheduled for the April-May 1964 timeframe, was postponed to address ongoing issues with the 3MV design and construction. But as the problems with the 3MV Mars spacecraft were being addressed, not the least of which was the growing consensus that the atmosphere of Mars was proving to be much thinner than assumed when the 3MV-3 lander was designed, it was realized that the ambitious plans to send a pair of 3MV-3 landers and another pair of 3MV-4 flyby spacecraft towards Mars in November 1964 had to be cancelled. Instead, a single 3MV-4A was launched towards Mars on an engineering test flight on November 30, 1964. Called Zond 2, there was little expectation that the spacecraft would actually survive all the way to Mars so it was purposely launched into a slow trajectory with a 249-day transit time to simulate a future Mars landing mission. If the spacecraft survived the long transit to Mars, it would be redirected towards an impact to become the first spacecraft to hit Mars but there were no plans to return any data (see “Zond 2: Old Mysteries Solved & New Questions Raised”). As feared, Zond 2 encountered problems right after launch and ground controllers lost contact three months before the spacecraft passed 1,500 kilometers above Mars on August 6, 1965 – three weeks after NASA’s successful Mariner 4 mission had reached the Red Planet (see “Mariner 4 to Mars”).

The New 3MV Missions to Venus

By the time of the launch of Zond 2, Soviet officials had already approved another round of 3MV missions to Venus with a total of four spacecraft for launch during the November 1965 window. These spacecraft were assigned the now defunct 3MV-3 and 3MV-4 designations of the Mars spacecraft that were never launched. The new 3MV-3 carried a roughly spherical lander with a diameter of 90 centimeters that would be released before its encounter to enter the Venusian atmosphere at a 43° to 65° angle to the local horizontal. The 383-kilogram lander would descend to the surface on a parachute while transmitting data from its instruments directly to Earth.

The 3MV-3 lander was equipped to measure the atmospheric temperature, pressure and composition, a photometer to measure light levels at various altitudes and a gamma ray detector to measure the concentration of radioactive elements like potassium, thorium and uranium in the surface rocks. A mercury level motion detector was also carried to measure the tilt of the lander and determine if the lander, which was designed to float, had made a water landing. At this time there was much uncertainty about the surface conditions on Venus and some astronomers still believed that Venus might support oceans. The 3MV-3 lander, like its 3MV-1 predecessor, was designed to withstand temperatures as high as 77°C and atmospheric pressures as great as five times that of Earth. Although this was on the low side of the consensus of surface conditions on Venus, at this time they were still anyone’s guess. The landers also carried a set of metallic pennants commemorating reaching Venus.

The new 3MV-4 flyby spacecraft carried a suite of instruments similar to its predecessors. A photo-television system equipped with a 200 mm lens would acquire a couple of dozen images on 25 mm photographic film as it passed over the day lit side of Venus. At a nominal range of 25,000 kilometers, the camera would produce images with a 3,100 kilometer wide field of view with a scale as good as about four kilometers per pixel. An ultraviolet spectrometer also shared the camera’s film system to make a series of spectra in the 285 to 335 nm wavelength range to study the atmosphere. The exposed film would then be developed automatically on board and the negatives scanned for transmission back to Earth. The high-definition quality images it generated were far superior to those returned by Mariner 4 at Mars. Also carried was an ultraviolet spectrometer operating in the 190 to 275 nm range to look for ozone and a two-channel infrared spectrometer to study the planet’s atmosphere and thermal emissions in the 7 to 38 μm wavelength range. The orbital compartments of both 3MV variants would also carry instruments to study magnetic fields, radiation, micrometeoroids, radio emissions as well as hydrogen Lyman-α and oxygen emissions in the ultraviolet.

Before these missions were launched, a test flight of the 3MV-4 was flown to verify the design changes made to the spacecraft after the failure of Zond 2. On July 18, 1965 the 960-kilogram 3MV-4 No. 3 was launched towards the Moon. Just over 33 hours after launch, what was called Zond 3 flew 9,219 kilometers above the lunar surface and secured 25 images and three ultraviolet spectra of the Moon including most of the lunar far side which had yet to be seen at that time. As Zond 3 continued on in the general direction of the orbit of Mars, the spacecraft developed its film and started transmitting its spectacular images on July 29. They revealed features as small as five kilometers and, along with the Luna 3 images taken in 1959, allowed Soviet scientists to map all but 5% of the lunar surface.

Zond 3 continued to operate as it travelled farther from Earth and towards the general direction of the orbit of Mars. In addition to engineering information, Zond 3 sent back data from its complement of instruments designed to study the interplanetary environment during the long cruise. On September 16, at a distance of 12.5 million kilometers, Zond 3 used its propulsion system to change the probe’s velocity by 50 meters per second to simulate a mid-course correction. The spacecraft successfully retransmitted its lunar images in mid-August, mid-September, and for the last time on October 23, when it was 31.5 million kilometers away from the Earth. By the time of the first 3MV launch to Venus in November 1965, Zond 3 had already operated for 117 days exceeding the expected transit time for the new Venera missions. Regular communication sessions with Zond 3 were maintained until March 3, 1966 when the craft was at a range of 153.5 million kilometers. After lasting for 228 days, Zond 3 had proven the 3MV design and set the stage for the new flights to Venus (see “The Soviet Zond Missions of 1963-65: Planetary Probe Test Flights“).

The Missions

The first up for launch was the flyby spacecraft designated 3MV-4 No. 4. Its 8K78M Molniya launch vehicle serial number U15000-042 lifted off from Site 31/6 at the Baikonur Cosmodrome in Soviet Kazakhstan at 05:02 UT on November 12, 1965. The Blok L escape stage and its 963-kilogram payload were successfully inserted into a 203 by 216 kilometer parking orbit with an inclination of 51.9° – the first time this lower inclination parking orbit was used on a Soviet planetary mission to help improve the launch vehicle performance. After a short coast, the Blok L ignited its engine and placed what was now called Venera 2 on course to Venus. Initial tracking of the spacecraft showed that everything was working as planned and that the trajectory was accurate enough to allow a flyby over the day lit side of Venus at a distance of less than 40,000 kilometers. It was decided that the scheduled course correction was not required since this was close enough for Venera 2 to meet its objectives.

Next up was the first lander-laden spacecraft, the 960-kilogram 3MV-3 No. 1. It lifted off from Site 31/6 at 04:19 UT on November 16, 1965 and was placed into a 213 by 293 kilometer parking orbit with an inclination of 51.9° by 8K78M serial number U15000-031. Once again, the Blok L did its job and sent Venera 3 on its way to Venus. For the first time, The Soviet Union now had two spacecraft in route to a planetary target. Initial tracking of Venera 3 showed that the spacecraft was in good health but that it would miss its target point which was 800 kilometers off from the center of Venus. On December 26, Venera 3 performed a course correct at a range of 12.9 million kilometers from the Earth. The 19.7 meter per second velocity change was sufficient to set Venera 3 on an impact course with Venus.

The last two Venera spacecraft would not fare as well as the first two. At 03:22 UT on November 23, 1965, 3MV-4 No. 6 lifted off atop of 8K78M serial number U15000-030. All was going well with the flight until 8 minutes and 48 seconds after launch while the Blok I third stage was completing its burn. One of the four combustion chambers of the stage’s 8D715K engine exploded due to a tear in a fuel pipeline. While the accident happened late enough to allow the rocket to enter a 227 by 310 kilometer orbit, the abnormal stage separation left the Blok L escape stage and its attached payload tumbling. With the Blok L unable to control its attitude and ignite its engine to send its payload to Venus, what would have been “Venera 4” was stranded and designated Kosmos 96. Its orbit finally decayed on December 9. The last attempt at the end of the 1965 Venus launch window to get the fourth 3MV on its way was suppose to take place on November 26. Unfortunately, a problem with the 8K78M rocket uncovered during launch preparations could not be repaired in the allotted time forcing a cancellation of the flight. Venera 2 and 3 would be on their own.

During the three-month cruise to Venus, both spacecraft made regular contact with ground controllers every few days. The Veneras responded to commands as well as transmitted engineering and scientific data from their suites of instruments. Unfortunately, the driving force for this effort, Sergei Korolev, would not live to see the outcome of this ambitious mission. On January 14, 1966 Korolev died unexpectedly during an operation to remove intestinal tumors. And not long after his passing, the two Venus-bound spacecraft encountered problems.

The first was Venera 2 which by February 10 was experiencing a dangerous increase in its internal temperature. This apparent malfunction in the thermal control system was having an adverse effect on spacecraft’s communications and control systems. The communication system on Venera 3 failed after a session on February 16 just 17 days out from Venus probably from its own overheating issue. Although the last communication session with Venera 2 was reportedly on February 27 just as it was approaching Venus, the session was of poor quality and there was no confirmation of the receipt of the pre-encounter commands.

Venera 2 made its closest approach over the day lit side of Venus at 02:52 UT on February 27, 1966 at a range of 23,950 kilometers. Whether or not the spacecraft ever made its observations of Venus is not known. All subsequent attempts to contact Venera 2 were unsuccessful and the mission was officially declared a loss on March 4. Had Venera 2 survived, it would have surely returned valuable information that would have revealed new discoveries as well as supplemented the data from NASA’s more modest Mariner 2 mission which had reached Venus three years earlier. But given the unbroken cloud layer that covers Venus, any images returned by Venera 2 would have shown a virtually featureless orb.

Attempts to contact Venera 3 after it was last heard from on February 16 were also unsuccessful. Based on tracking information, there is little doubt that Venera 3 entered the Venusian atmosphere at 06:56 UT on March 1, 1966 somewhere on the night side near the terminator between 20°S and 20°N latitude and 60°E and 80°E longitude. Although no telemetry was received from the lander, it had become the first manmade object to impact another planet. But even if it had survived the trip to Venus, it would have never reached the surface intact as planned. Later testing of the lander design showed that its ability to survive an entry at hundreds of Gs was questionable. And even if it had survived the atmospheric entry, the 3MV-3 lander would have been crushed during descent at an altitude of about 35 kilometers because the atmosphere of Venus was almost 20 times denser than Soviet engineers or many astronomers had assumed. At best, the Venera 3 would have returned some useful in situ measurements of the atmosphere during its descent before it was lost.

The loss of both Venera spacecraft was a huge blow that was only partially softened by the propaganda victory of Venera 3 at least impacting Venus. A subsequent investigation into the failures indicated that problems with paint on the thermal radiators degrading over time was responsible for the loss of this batch of 3MV spacecraft – an issue that would not have as severely affected the Zond 3 test flight directed farther away from the Sun. Unfortunately these lessons had come too late to salvage the prestige of the engineers at OKB-1 who originally designed the 3MV. Back in April 1965, responsibility for all Soviet robotic lunar and planetary missions was transferred to NPO Lavochkin so that OKB-1 could concentrate its resources on crewed spacecraft missions such as the then new Soyuz 7K-series being developed for orbital and lunar missions (the same Soyuz whose modernized descendants still fly today). By the time of the Venera 2 and 3 missions, the engineers at NPO Lavochkin under Chief Designer Georgi Babakin were already busy reassessing the 3MV spacecraft design. With the next launch of a Mars mission pushed back to 1969 as a totally new spacecraft was designed, Lavochkin would have a chance to prove itself during the next opportunity to launch missions to Venus in the late spring of 1967 using their significantly upgraded “1V” design (see “Venera 4: Probing the Atmosphere of Venus“).

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Related Reading

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

“You Can’t Fail Unless You Try: The Soviet Venus & Mars Missions of 1962”, Drew Ex Machina, November 1, 2017 [Post]

“The Soviet Zond Missions of 1963-65: Planetary Probe Test Flights”, Drew Ex Machina, April 18, 2019 [Post]

“Venera 4: Probing the Atmosphere of Venus”, Drew Ex Machina, October 21, 2017 [Post]

General References

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

Wesley T. Huntress 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

Timothy Varfolomeyev, “Soviet Rocketry that Conquered Space – Part 5: The First Planetary Probe Attempts 1960-1964”, Spaceflight, Vol. 40, No. 3, pp 85-88, March 1998